Turbomeca - Cleaning, Washing and Rinsing of Turboshaft Engines_Comparison of Turbomeca Procedures, Customer Studies and the Problem of Volcanic Ash.pdf

R APPORT

DES

STAGE

T ECHNIQUE

INTERNSHIP TECHNICAL REPORT

ÉMETTEUR/ FROM: UNHELK AR V AIBHAV

CLEANING, WASHING AND RINSING OF TURBOSHAFT ENGINES COMPARISON OF TURBOMECA PROCEDURES, CUSTOMER STUDIES AND THE PROBLEM OF VOLCANIC ASH

ENR0090-D Ce document est la propriété de la société Turbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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CONTENTS 1

Purpose __________________________________________________ 6

2

Introduction _______________________________________________ 6

3

Approach towards Analysis __________________________________ 6

4

Turboshaft Engines _________________________________________ 7 4.1

Basic Architecture ________________________________________________________ 7

4.2

Operation ________________________________________________________________ 8

4.3

Categories _______________________________________________________________ 9

4.4

Arrius __________________________________________________________________ 10

4.5

Arriel___________________________________________________________________ 10

4.6

Makila __________________________________________________________________ 11

4.7

Comparative Study _______________________________________________________ 12 4.7.1 Engine Application___________________________________________________ 12 4.7.2 Performance Parameters______________________________________________ 13 4.7.3 Physical Parameters _________________________________________________ 14 4.7.4 Engine Architecture __________________________________________________ 14 4.7.5 Cleaning Related Parameters __________________________________________ 16

5

Cleaning, Washing and Rinsing – Turbomeca Procedures ________ 18 5.1

Nomenclature ___________________________________________________________ 18

5.2

Rinsing_________________________________________________________________ 20 5.2.1 Generic Procedure ___________________________________________________ 20 5.2.2 Difference Between Engines___________________________________________ 21 5.2.3 Comments__________________________________________________________ 22 5.2.4 Rinsing Products ____________________________________________________ 22

5.3

Washing ________________________________________________________________ 23 5.3.1 Generic Procedure ___________________________________________________ 23 5.3.2 Difference Between Engines___________________________________________ 23 5.3.3 Comments__________________________________________________________ 24 5.3.4 Washing Products ___________________________________________________ 25

5.4

Cleaning ________________________________________________________________ 26 5.4.1 Generic Procedure ___________________________________________________ 26 5.4.2 Difference Between Engines___________________________________________ 27 5.4.3 Comments__________________________________________________________ 28

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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5.4.4 Cleaning Products ___________________________________________________ 29 5.5

Frequency ______________________________________________________________ 30 5.5.1 General Cases ______________________________________________________ 30 5.5.2 Specific Cases ______________________________________________________ 31

6

7

5.6

Tools___________________________________________________________________ 31

5.7

Products used ___________________________________________________________ 33

5.8

Cautions - Health, Safety, Environment ______________________________________ 35

Cleaning, Washing and Rinsing – Customer Studies ____________ 36 6.1

Australia________________________________________________________________ 37

6.2

North America ___________________________________________________________ 38

6.3

North Sea _______________________________________________________________ 39

6.4

Asia Pacific _____________________________________________________________ 41

6.5

Summary _______________________________________________________________ 42

Cleaning, Washing and Rinsing – Experiences Outside Turbomeca 43 7.1

Nomenclature ___________________________________________________________ 43

7.2

Literature Survey_________________________________________________________ 44 7.2.1 Introduction ________________________________________________________ 44 7.2.2 Evolution___________________________________________________________ 44

7.3

8

Summary _______________________________________________________________ 46

Volcanic Ash - Introduction _________________________________ 47 8.1

Fundamentals ___________________________________________________________ 47 8.1.1 Volcanoes __________________________________________________________ 47 8.1.2 Volcanic Eruptions___________________________________________________ 48 8.1.3 Volcanic Ash________________________________________________________ 49

8.2

Volcanic Ash and AVIATION _______________________________________________ 50 8.2.1 Background ________________________________________________________ 50 8.2.2 Effect on Aviation____________________________________________________ 51 8.2.3 Effect on Aircrafts ___________________________________________________ 52 8.2.4 Notifications and Warnings____________________________________________ 55 8.2.5 Fly Zones __________________________________________________________ 56

9

Volcanic Ash and ENGINES _________________________________ 58 9.1

Major Effects ____________________________________________________________ 58

9.2

Ash Ingestion – An Estimate _______________________________________________ 59

9.3

Other Contaminants ______________________________________________________ 61

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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9.3.1 Sand ______________________________________________________________ 61 9.3.2 Chemical Environment _______________________________________________ 62 9.3.3 Comparison With Volcanic ASH ________________________________________ 62 9.4

Engine Maintenance ______________________________________________________ 63 9.4.1 Current Procedures __________________________________________________ 63 9.4.2 Service Bulletins ____________________________________________________ 64 9.4.3 Suggestions – Engine Cleaning ________________________________________ 66 9.4.4 Suggestions – Service Bulletins________________________________________ 67

9.5

Long Term Solutions _____________________________________________________ 69 9.5.1 Filters _____________________________________________________________ 69 9.5.2 Electromagnetic Properties ___________________________________________ 69 9.5.3 Development of Solutions_____________________________________________ 69 9.5.4 Engine Design ______________________________________________________ 70 9.5.5 Summation _________________________________________________________ 70

10 References _______________________________________________ 70

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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1 PURPOSE The study presented on the topic of “Cleaning, Washing and Rinsing of Turboshaft Engines: Comparison of Turbomeca Procedures, Customer Studies and the problem of Volcanic Ash“ is performed as requirement towards the Internship (Stage) at the TURBOMECA Support Department in Turbomeca, Tarnos under the guidance of M. PEROT Philippe. The study aims to realign the current knowledge on Engine Cleaning and provide solutions for the problem of Volcanic Ash. Turbomeca documents (Training and Maintenance Manuals) and studies from open literature (research publications and the internet) were the primary resources used for the study. Timely suggestions and advice from the Mentor, Training Centre and Engineers at the Support department in Tarnos were illuminating as well as useful, and I would like to thank them for the same. Lastly, I would like to express my gratitude towards the Turbomeca and the Indian Institute of Technology, Bombay for providing the opportunity and resources to carry out the following study.

2 INTRODUCTION To maintain the operation of engines in variety of conditions proper maintenance is essential. The operations of Rinsing, Washing and Cleaning are one of the primary tasks used in maintainability, in order to prevent corrosion and deterioration of engine, and performance recovery, in order to recover efficiency, torque margin and temperature margins, of Turboshaft Engines. Rinsing (Rincage), Washing (Lavage) and Cleaning (De-crassage) though seemingly trivial tasks affect the performance as well as the maintenance cost of an Engine very drastically. The operation of Rinsing, Washing and Cleaning becomes even more important to Helicopters due to the specific nature of their operations; such as, near surface operations in sandy, saline or polluted atmosphere, landing/take-off in unpaved (hence, dust-prone) areas, and last but not the least the on-going problem of Volcanic Ash (the Icelandic eruptions of Eyjafjallajokull). Based on a detailed literature survey and engineering analysis, this document intends to underline the importance of Rinsing, Washing and Cleaning procedures specifically for Helicopter (Turboshaft) Engines. Finally, this document presents an overview of some approaches, validation of the current procedures and a few solutions with regards to the protection and maintenance of Turboshaft engines affected by the Volcanic Ash.

3 APPROACH TOWARDS ANALYSIS A top-down approach was adopted in the overall analysis wherein the work was divided into the following broad sections, namely, • Comparative analysis of various TURBOMECA Turbo-shaft engines • Various aspects of Rinsing, Washing and Cleaning of Turbo-shaft engines o Validation of the current Turbomeca procedures o Comparison of the current procedures for different engine families ( ranging from MTOW of 2-3 Tonnes to that of 11-12 Tonnes ) o Customer Experiences o Compilation and Survey of other procedures (apart from that of Turbomeca) • Effect of Volcanic Ash on Turbo-shaft Engines • Solutions for Performance Recovery and Operations of Engines affected by Volcanic Ash ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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4 TURBOSHAFT ENGINES Turboshaft engines are the gas-turbine engines that convert the chemical energy in fuel and air into mechanical energy on a shaft. The turbo-shaft engines find application in various industries apart from aviation. The mechanical energy on the shaft can be used for various purposes, such as, helicopter rotors, electric generator and hydraulic pumps.

FIGURE 1: ARRIEL – A Free-Turbine Turboshaft Engine First, basic architecture and operation of a turboshaft engine is described. Thereafter, detailed information is documented for the specific TURBOMECA engines under consideration, and a comparative analysis has been made. NOTE: Although, this document is focused on application of turbo-shaft engines on Helicopters; it should be borne in mind that the problems (and consequently their solutions) related to Rinsing, Washing and Cleaning of similar nature also arise in land and marine turbines, and that the experience on land and marine turbines could be used for improving the Rinsing, Washing and Cleaning for helicopter applications.

4.1

BASIC ARCHITECTURE

Different types of turbo-shaft engines exist with differing architecture, technology and application, but few basic components are found in all the turboshaft engines. These include: • Air Intake • Compressor Section o Axial Compressor, and/or o Centrifugal Compressor • Combustion Chamber • Turbine Section • Output Power Shaft • Exhaust System ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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FIGURE 2: Fundamental parts of a free-turbine Turbo-shaft engine A shaft connects the compressor section to the turbine section; which is required since the turbine section provides the energy to drive the compressor section. The following figure shows the main components of a turboshaft engine. These components are present on all the turboshafts but their position, number and architecture might vary.

4.2

OPERATION

The engine provides power by transforming the energy in the ambient air and fuel into the mechanical energy on the shaft. The process of this conversion consists of the following steps:

• •

FIGURE 3: Main Operating Phases of Gas Turbine Engines Admission o Ambient air is admitted through the Air Intake Compression o The ambient air is then compressed by the Compressors in the system o The air is taken to a very high pressure

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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•

•

•

4.3

Combustion o The compressed air is combined with the fuel o The gas mixture is burnt in the Combustion Chamber to produce thermal energy o This also results in a very high temperature o The performance of gas-turbine engines is usually limited by the material properties of the Combustion chamber Expansion o The hot gas expands in this section and drives the Turbines o The gas pressure and temperature drops o The thermal energy is converted into shaft mechanical energy Power transmission o The power is transmitted to the output shaft o Generally, a reduction gearbox is used to reduce the angular speed of the output shaft

CATEGORIES

As there are various types of helicopters, there are various types of engines which provide them with power. The turboshaft engines are mainly of two types: • Single shaft turboshaft engines o The compressor-turbine shaft in directly connected to the output shaft o Has a robust and simplistic design o Suitable for single-engine helicopter operation • Free Turbine turboshaft engines o Has two separate rotating assembly, which may or may not operate in the same direction
The first assembly is called the Gas Generator, it is the compressorturbine shaft
The second assembly is the one that drives the Power Turbine (also known as the free turbine) and is connected to the output shaft o Found in various configurations, such as
Rear power drive
Front power drive • Through an internal/coaxial shaft • Through an external shaft o Offers greater flexibility and can be used for twin-engine operations Apart from their architecture, the turboshaft engines can also classified by their size, output power, design of intake, etc. In this document only free-turbine turboshaft engines are considered. The following engines of varying architectures are chosen for analysis, namely: • Arriel 1 S1 • Arriel 2 S2 • Arrius 2 B2 • Makila 2 A The said engines are chosen since they span the range of modular free turbine turboshaft engine and provide power to various helicopters ranging from a MTOW of 2 to 11 tons. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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4.4

ARRIUS

Arrius is a family of free turbine turboshaft engines with an integral reduction gearbox and front power drive with a power output of 357 – 530 kW. The engine family is specifically designed to power light single and light twin engine helicopters in the 2-3 ton range. The engine family has the smallest engines of the Turbomeca Turboshaft family of engines, and hence has the least power output. The engine though modular, consists of only two modules, owing to its size and application. In comparison with the other engines it is void of any axial compressor stage, and relies totally on the centrifugal compressor for developing the pressure required for combustion. The variant Arrius 2 B2 was released in the year 2002, and is used to power the Eurocopter helicopter EC135 with a MTOW of 2910kg.

FIGURE 3: Engine Architecture – Arrius 2B 2

4.5

ARRIEL Arriel is a family of free turbine turboshaft engines with external power transmission shaft and forward power drive and a power output of 478 – 704 kW. The engine family has produced 9000 engines till date and has flown for more than 30 million hours in over 100 countries. Out of its 28 variants we shall be discussing two, namely, Arriel 1 S1 and Arriel 2 S2. It is one of the most used engines of the Turbomeca family and was introduced into service as early as 1977. It has been used for over 15 helicopter types in 110 countries and due to continuous evolutions and modification is still being used for a lot of applications. The variant Arriel 1 S1 powers the twin engine medium lift Sikorsky S76A+, S76A++ and S76C helicopters, and is developed for off-shore missions.

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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FIGURE 4: Engine Architecture – Arriel 1S 1 The variant Arriel 2 S2 was certified in 2005 and powers the twin engine medium lift Sikorsky S76C++ helicopters.

FIGURE 5: Engine Architecture – Arriel 2S 2

4.6

M AKILA

Makila is a family of free turbine turboshaft engines with a rear direct power drive and with a power output of 1300 – 1600 kW. Due to the higher power output, owing to its size and design, the Makila family is used to power the heavier helicopters. Another, salient feature of Makila engines is the rear power drive allowing engine installation in front of the rotor and drastically reducing the intake losses. The variant Makila 2 A certified in 2004, powers the military helicopter Eurocopter EC 725 and its civil variant Eurocopter EC 225.

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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FIGURE 6: Engine Architecture – Makila 2A

4.7

COMPARATIVE STUDY

This section enlists a comparative study of variety of parameters of the engines discussed above. The section is divided into five parts, each part comparing parameters of different sub-systems in regard to turboshaft engine.

4.7.1 ENGINE APPLICATION Firstly, we have an overview of the application of the said engines on various helicopters, in order to have an estimate of performance and capability of the engines.

Helicopters MTOW (kg) Introduction TBO

Arriel 1S 1 Sikorsky S 76 A+ Sikorsky S76A++ Sikorsky S 76 C

Arriel 2S 2 Sikorsky S 76 C++ (twin engine)

Makila 2A EurocopterEC725 EurocopterEC225 (twin engine)

Arrius 2B 2 Eurocopter EC 135 (twin engine)

1986 3000

5306 2004 4000

11200 2003 3500

2910 2002 3500

TABLE 1: Applications – Comparative Study of free-turbine Turboshafts • • •

We can see that the Makila family powers the heaviest of the aircraft and requirements for the same shall be reflected in its physical and performance parameters. The value of TBO(in hours) is comparable for all of the engines, and continuous efforts are made in order to increase its value. All the Type 2 engines are relatively recent and hence use newer technologies and provide better performance.

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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4.7.2 PERFORMANCE PARAMETERS Arriel 1S 1 575 541 4.29

Arriel 2S 2 688 621 4.5

Makila 2A 1563 1395 5

Arrius 2B 2 479 439 3.85

Pow/G (Specific Power)

216.4

214.13

219.34

211.05

SFC EGT ( °C ) TBO (hours)

600 3000

390 670 4000

280 550 3500

700 3500

MTOP (kW) AEO MCP (kW) Power/DryMass

TABLE 2:Performance Parameters – Comparative Study of free-turbine Turboshafts NOTE: All the parameters are listed at their respective standard conditions • •

•

•

•

Owing to its size Makila produces the highest power, over thrice that of the Arrius Power/Dry Mass o Power output per unit of mass of the engine – This parameter indicates the amount of Power produced per unit of dry mass of the engine and has the units of kW/kg o Ideally, the user would want this parameter to be as high as possible o It is highest for Makila 2A (~5) and lowest for Arrius 2B2 (~3.85) o This metric indicates that “As the size of the engine grows the extra weight required to produce the marginal power reduces" o This result is intuitive since after the basic weight for engine has been accounted for (which is necessary in all the engines) the extra weight for one stage of compressor would produce enormous increase in output power o However, care should be taken that the trend observed might not be universal
Shall depend heavily on the design of the engines
The trend might show a global peak after which adding extra compressors will not result in increase of “Power/Dry Mass” ratio Power/G o Power output per unit of air flow into the engine – This parameter indicates the amount of power generated by the engine when the mass flow is 1 kg/s o Units: kW*s / kg OR kJ/kg o This normalized metric gives a way of comparing efficiency and technology of various engines o The value of this parameter is in the same range for all the engines indicating some similarity in design and efficiency SFC o Specific Fuel Consumption – Quantity of fuel necessary to produce one kW of power per unit of time (usually hour) o Values of SFC are dependent on the engine design which is in turn dictated by the requirement from helicopter. A lower value of SFC is always preferred. EGT o Exhaust Gas Temperature – Indicates the temperature of the exhaust gases o It should be as low as possible for two reasons

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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o

Higher temperature indicates more energy can be extracted from the flow, i.e. the engine is performing at lesser efficiency
For environmental reasons (Green engines) Arrius has the highest EGT of 700 °C

4.7.3 PHYSICAL PARAMETERS

Variant Type Power Drive Modules Dry Mass (kg) Dimension (mm)

Arriel 1 S1 Free Turbine Forward 5 126 1166 465.5 609

Arriel 2 S2 Free Turbine Forward 5 138 1166 465.5 609

Makila 2 A Free Turbine Rear 4 279 2115 785 668

Arrius 2 B2 Free Turbine Forward (IRG) 2 114 1158 518 690

TABLE 3: Physical Characteristics – Comparative Study of free-turbine Turboshafts • • •

• •

All the engines are modular free turbine turboshaft engines Although, all the engines are modular the number of modules vary - wherein Arrius family has as low as 2 modules and Arriel family has 5 modules Makila 2A o Is the largest in terms of both the size and weight o Differs in the overall layout as it has a rear power drive: this permits
Engine installation in front of the rotor and
Significantly reduces pressure loss due to air intake. Arrius 2B 2 o Is the smallest and the lightest, which reflects in its capacity and MTOP. Arriel o Dimensions of Arriel 1S1 are given different on the Turbomeca Site and Training Manual – Different conventions for measuring the length have been observed.

4.7.4 ENGINE ARCHITECTURE Next, we compare the basic engine architecture of the four engines: • Air Intake o All the engines have an annular air intake o Engines except Arrius have a dynamic intake
Which means that they have a frontal intake
Even when the engine is not switched on there is air flow through the engine
Arrius on the other hand due to installation constraints does not have a frontal intake o G, Air Mass flow (kg/s)
Amount of air introduced into the engine per unit of time
Is highest for the Makila engines and least for Arrius ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Intake G Axial Compressor Stages Pressure Ratio Material Centrifugal Compressor Pressure Ratio Material Diffuser Stages Combustion Chamber Geometry Fuel Injection Max. Temp. Gas Generator Turbine Geometry Stages N1 (100%) – RPM Power Turbine Geometry Stages N2 (100%) – RPM Power Shaft Drive NR – RPM

Arriel 1S 1 Dynamic, Annular 2.5

Arriel 2S 2 Dynamic, Annular 2.9

Makila 2A Dynamic, Annular 6.36

Arrius 2B 2

1 1.5 Titanium Alloy

1 1.6 Titanium Alloy

3 2.65 Titanium Alloy

Nil Not Applicable Not Applicable

5.4 Titanium Alloy 2

5.12 Titanium Alloy 2

4.25 Titanium Alloy 2

9.1 Titanium Alloy 2

Annular Centrifugal 2500

Annular Centrifugal 2500

Annular Centrifugal 2500

Annular Reverse Flow 2500

Axial 2 52000 ACW

Axial 1 52110 ACW

Axial 2 33200 ACW

Axial 1 44038 CW

Axial 1 41600 CW Front 6000

Axial 1 39095 CW Front 6000

Axial 2 22962 ACW Rear / Bendix 22962

Axial 1 54117 ACW Front 5898

Annular 2.08

TABLE 4: Engine Architecture – Comparative Study of free-turbine Turboshafts •

Axial Compressor o Is absent in Arrius engine o Makila has a 3 stage axial compressor with a pressure ratio of 2.65

•

Centrifugal Compressor o Arrius has the highest pressure ratio of 9.1 as whole of the compression is done by the centrifugal compressor o Both the Axial and Centrifugal compressor are made of Titanium alloys o Two divergent diffuser stages are present after the centrifugal compressor in order to increase the pressure, decrease the velocity and straighten the flow

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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o

Overall pressure ratio (across both the compressors) is highest for Makila (~11.26) and least for Arriel 1 (~8.1)

•

Combustion Chamber o Arrius has fuel injection with reverse flow; while Arriel and Makila have centrifugal fuel injection o This design difference is reflected in various other engine parameters
Size of the engine
Turbine Entry Temperature
Exhaust gas temperature o The maximum temperature in the engine is at the Combustion Chamber and is 2500°C for all the engines. This is due to the mate rial limitations which are present for all type of engines and limit their design and performance

•

Gas Generator Turbine o Arriel 1S1 and Makila 2A have two stages of Gas Generator Turbine while Arriel 2S2 and Arrius 2B2 have single stage Gas Generator Turbine
This is one of the main difference in the architecture of Arriel 1S1 and 2S2 o Due to the velocity vector triangles Arrius gas generator turbine moves in CW (seen from behind) while for the rest of engines it moves in ACW direction o N1 denotes the rotation speed of Gas Generator section is highest for Arriel and least for Makila

•

Power Turbine o Makila being the largest engine has two power turbine stages o Arrius has the highest power turbine speed while Makila has the least

•

Power Shaft Drive o Speed of the power shaft drive is very high for Makila 2A, this is because of the fact that the Makila has a rear direct power drive and no reduction gear box o After reduction gearbox the rotation speed of the engine rotors is comparable for various helicopters and is in the range of 5000-7000 RPM

4.7.5 CLEANING RELATED PARAMETERS Since, the main focus of this study is to analyze Cleaning procedures of the said engines; we shall see in brief some parameters related to the engine cleaning. The operation of Cleaning is covered in more detail in further sections.

In-built Washing System

Arriel 1S 1

Arriel 2S 2

Makila 2A

Arrius 2B 2

No

No

Yes

Yes Inlet Grid

Intake Protections

Sand Filter/EAP/Vortex filter/Barrier filter (Optional)

Barrier Filters/ EAP (optional)

Related Problems

Sand Accumulation in Hollow Shaft and Cleaning of Turbine Section

Cleaning of Turbine Section

TABLE 5: Cleaning Parameters – Comparative Study of free-turbine Turboshafts ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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•

Washing System o An inbuilt washing/cleaning manifold exists for the engines Makila and Arrius 2B2 o Arriel on the other hand has washing systems based on the helicopter, details of which can be found in the Aircraft Maintenance Manual

•

Intake Protections o For the Arrius engines an Inlet Grid is present in order to protect the engines from Foreign Object Damage o Makila and Arriel engines have an option of installing Sand Filters or Barrier Filters to protect the engine and filter the incoming air flow. o These measures are particularly important and sometimes necessary for flights in sand-laden or volcanic ash affected atmosphere.

•

Cleaning Related Problems o Cleaning, Washing and Rinsing are scheduled maintenance task to recover performance of the engine, but at times they are used in case some specific problem arises o Arriel engines consist of a hollow shaft which might get accumulated with sand or dirt depending on operating conditions and can cause vibration. To restore the performance cleaning of hollow shaft is to be performed. However, it should be noted that this is not a Line 1 maintenance task. o Makila engines because of their length might encounter some problems in cleaning of aft stages of the compressor and turbine stages o Apart from this cleaning operation is used in order to recover T4.5 margin and/or Torque margin based on Power Assurance Check

Now, with the basic knowledge of turboshaft engines, we move on to the analysis of Cleaning, Washing and Rinsing for Turboshaft Engines.

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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5 CLEANING, WASHING AND RINSING – TURBOMECA PROCEDURES The procedures of Cleaning, Washing and Rinsing are some of the most important and effective tasks for performance recovery of engines. The tasks are mandatory for all sorts of gas turbine engines, land-based or aviation, turbojet or turbofan, and so on. In this section, we shall be concentrating on the specific procedures for Turboshaft engines specified by Turbomeca, followed by their comparison and analysis with external Cleaning, Washing and Rinsing procedures in the next section. Furthermore, the cleaning of engines is performed in all levels of maintenance, albeit with varied sophistication and technique; here we shall be specifically focusing on procedures specified for 1st Line Maintenance. “Cleaning, Washing and Rinsing” are very broad and generic terms, hence, numerous definitions and interpretations can be derived, making the technical communication and any further discussion not just confusing but at times misleading. Thus, at the outset, we shall get introduced to the nomenclature and definitions of the seemingly-trivial but nonetheless important operations of “Cleaning, Washing and Rinsing” in context of turboshaft engines.

Figure 7: Typical Equipment for Compressor Cleaning This section is heavily derived from the information obtained from “Turbomeca Maintenance Manuals” and “Technical Specifications”, and from the vast amount of data in these publications relevant information has been extracted, analyzed and compiled. In this section, firstly we see the existing Turbomeca procedures for Rinsing, Washing and Cleaning, respectively. For each of the process a generic description is provided followed by detailed comparison of the process for the three turboshaft engines, namely, Arriel 2S2, Arrius 2B2 and Makila 2A. Each section concludes with comments on ambiguities in the current procedures and suggestions for improvements. Lastly, all the information related to operations of “Cleaning, Washing and Rinsing”, i.e. details about necessary Cleaning Products, Safety, Frequencies, Tools and Equipments, is compiled. With all this information, we shall be equipped with ample background and clarity of jargon to understand the evolution, comparison and analysis of the “Cleaning, Washing and Rinsing” procedures apart from that of Turbomeca, which are covered in the next section.

5.1

NOMENCLATURE Cleaning, Washing and Rinsing – are words that are so similar that without having a formal technique definition it is difficult if not impossible to carry forward any analysis. The Oxford dictionary defines the three processes as follows

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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• • •

Cleaning – getting rid of dirt, impurities and extraneous substances Washing – cleaning with water Rinsing – washing quickly with water and no soap

One can quite easily see that the generic definitions of these processes are not enough and hence in context of maintenance of engines we define them as follows • Cleaning – Operation to clean the engine and remove corrosive deposits using an aqueous solution of concentrated cleaning product (15 to 25%). • Washing – Operation to remove corrosive, crystallized salt deposits by an aqueous solution of weakly concentrating cleaning product (2 to 5%) o Washing for engine running, operation carried out with the engine running o Washing during ventilation/Cranking, operation carried out with the engine shutdown (with the starter-generator). • Rinsing – Operation to remove salt deposits using only water (and an anti-freeze if necessary) Similarities exist between the technical definitions and the dictionary meanings, but some additional conditions are imposed on each operation differentiating it from its generic description. Some of the differences between the processes are listed as follows:

Tools Pressure GeneratorNozzle Washing System Products Required Distilled Water Chemicals Percentage of Chemicals Periodicity Daily Weekly Performance Recovery Effluent Removed Salt Dirt Procedure Engine Running Cranking/Ventilation

Cleaning

Washing

Rinsing

Y Y

Y Y

Y Y

Y Y ~20

Y Y ~2

Y N 0

Y Y

Y Y Y

Y Y Y

Y

Y -

Y -

N Y

Y Y

Y Y

Table 6: Comparison of Cleaning, Washing and Rinsing The above table lists some of the main parameters of interest in the operations related to engine cleaning. In the next sections, we shall see the same parameters in more detail and comparison of the processes for engines of varying architecture. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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5.2

RINSING Rinsing is the process of removing salty deposits in the gas path of an engine using only water (and anti-freeze products depending on the ambient temperature). It is the most basic of the task of cleaning, washing and rinsing; and hence is usually recommended to be done daily after the last flight of the day (EDF).The task usually can be performed either with the engine running or by cranking. Rinsing by cranking is recommended as it is more efficient, but operators might prefer rinsing “with the engine running” as it is less time-consuming.

5.2.1 GENERIC PROCEDURE Procedure for Rinsing is specific to each engine, but there are a few common tasks that are performed in rinsing of all engines; the specific numeric parameters (amount of fluid, time required, etc.) usually vary. The procedure of Rinsing can be divided into the following basic steps: •

• • •

• •

•

Preparation of Rinsing mixture o Quantity of mixture o Percentage of Constituents ( Demineralised Water and Anti-Icing Agent) o Homogenization Aircraft Settings o Blanking of Bleed Valve o Closing all the aircraft manufacturer bleed valve Tool Settings o Connection of the tool o Pressure/Flow settings of the tool Injection of Rinsing Mixture o Cranking
Number of times
Amount of time
Flow speed o Engine Running
N1 specification
Amount of time
Flow Speed Removal of Equipment o Of tools o Of blanks on valves Drying of the engine o Time o Procedure o Exceptions Post-maintenance Procedure o Internal Protection o External Protection

The factors listed in italics above are the specific numerical parameters which differ from engine to engine and are based on – size of the engine, number of compressor stages and properties of the engine washing system. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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5.2.2 DIFFERENCE BETWEEN ENGINES Now we tabulate the differences between the specified procedures for Rinsing for the three engines:

Rinsing Mixture Quantity Consumables Percentage Homogenization

Arriel 2S2

Makila 2A

Arrius 2B2

Necessary Anti-icer not mentioned

7 litre

3.5 litre

Demineralised Water

Not Mentioned

Not Mentioned Not Mentioned

Anti-Icer As per CCT_00800_C As per CCT_00800_C Mentioned Mentioned

Aircraft Settings

Manufacturer Air Bleeds Tools Settings Flow Speed Washing System Injection Engine Running Cranking Drying Time (seconds) Additional Provisions

Mentioned

Mentioned

Not Mentioned

2-3 l/min

2-3 l/min

Based on the Tool

Aircraft Based

Present in Engine

Present in Engine

Listed in MM Not Listed in MM

Listed in MM Listed in MM

Listed in MM Listed in MM

30

300 Internal Protection External Protection

300 Internal Protection External Protection

Not listed

Table 7: Comparison of Rinsing Procedure As can be seen from the comparison, lot of differences exists in the numerical parameters related to Rinsing for various engines: • Quantity of Rinsing Mixture o Is least for Arrius and highest for Makila o Directly depends on the size of the engine • Settings of the Tools o Depending on the engine size, design of the tool and amount of flow required differing flow speeds are specified for the engines • Drying of the Engine o Amount of time required for drying Arriel Engine is 30 seconds o Reason for the same is not known • Fluid Injection o Rinsing by Cranking (Ventilation) is not listed for Arriel engine ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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In the table, it can be seen that a lot of parameters are not clearly specified in the Maintenance Manuals; hence, next we list a few comments about the procedure and suggestions for the same.

5.2.3 COMMENTS Due to various reasons such as translation, communication and human factor, any procedure is bound to have some ambiguities. Since, the procedures are used by customers in 1st Line maintenance it is of utmost importance, for safety of both the engine and the customer, that the procedures be verified and be made as clear and succinct as possible. This verification of procedures should be done not only for technical details but also for semantics (wordings) and clarity. Listed below are some such points in the procedure which might be confusing and can lead to an improper execution of the maintenance task: •

•

• •

Consumables o The products required for rinsing are not mentioned in consumables in procedures of Arrius 2B2 and Arriel 2S2 o Although, they are mentioned separately elsewhere in the procedure/Maintenance Manual Arriel 2S2 o Rinsing during Cranking not mentioned in the Maintenance Manual. This should be included o Quantity and Percentage of Rinsing Mixture not mentioned in the Maintenance Manual o Time for drying is drastically less. This might be a printing mistake. Makila 2A o "CAUTION" for monitoring T4.5 mentions cooling the engine naturally, while in other engines ventilation can be used Arrius 2B2 o Not mentioned in the procedure to close the aircraft manufacturer bleeds o Not mentioned in the procedure to monitor N1 drop

5.2.4 RINSING PRODUCTS Rinsing means washing engine without any chemicals, yet based on ambient temperature following anti-freeze products must be used: 5.2.4.1

DESIGNATION

Anti-freeze product Validated products (recommended)

Isopropyl alcohol

Products authorized for use (replacement)

Pure methanol (AIR 3651) 44/56 or 50/50 methanol/water

Water quality Distilled water Demineralised water Minimum quality of water

Table 8: Rinsing Products ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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5.3

WASHING Washing involves a desalting operation to remove Corrosive, Crystallized salt deposits by an aqueous solution of weakly concentrated cleaning product (2-5%). The procedure can be carried out in two ways, namely During Engine Running and During Ventilation/Cranking.

5.3.1 GENERIC PROCEDURE The generic procedure for Washing is similar to that of Rinsing, except for the fact that Cleaning Products to the tune of 2 to 5% are used while Engine Washing, while only distilled/demineralised water is used for Engine Rinsing.

5.3.2 DIFFERENCE BETWEEN ENGINES Now we tabulate the differences between the specified procedures for Washing for the three engines:

Quantity Consumables Percentage Homogenization

Arriel 2S2 Necessary Washing Product Demineralised Water Anti-Icer Ambiguity in % Mentioned

Makila 2A Arrius 2B2 7 litre 3.5 litre Washing Product Not Mentioned Demineralised Water Anti-Icer As per CCT_00800_C As per CCT_00800_C Mentioned Mentioned

Aircraft Settings

Manufacturer Air Bleeds Tools Settings Flow Speed Washing System Injection Engine Running N1 N1 drop Cranking

Mentioned

Mentioned

Not Mentioned

2-3 l/min Aircraft Based

2-3 l/min Present in Engine

Based on the Tool Present in Engine

Listed in MM 68% 15% Listed in MM

Listed in MM Ground Idle 10% Listed in MM One or more ventilations of 15 seconds no rinsing

Listed in MM Ground Idle Not Mentioned Listed in MM One or more ventilations of 15 seconds no rinsing

2 ventilations of 20 seconds 1 rinsing of 15 seconds Drying Time (seconds)

30(engine running) 300 (during ventilation)

300

300

Additional Provisions

Not listed for Engine Running

Internal Protection External Protection

Internal Protection External Protection

Table 10: Comparison of Washing Procedure ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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As mentioned earlier the procedures of Rinsing and Washing have a lot of similarity, in fact except for the difference in Washing Mixture and the procedure of Mixture Injection the methods are identical. For some engines, Rinsing hence is not defined separately and integrated into the procedures of Cleaning and Washing. • Quantity of Rinsing Mixture • Settings of the Tools • During Engine Running o Value of N1 –
A minimum N1 has to be maintained for proper flow of air and washing fluid during engine washing
The value of N1 is engine specific
Furthermore, a drop(10 – 15%) in this value of N1 can be tolerated during the washing procedure • During Cranking o Number of ventilations
Arriel - Two ventilations of 20 seconds each are specified
Makila and Arrius – One or more ventilation of 15 seconds o Rinsing
Literature indicates that it is a nice practice to rinse out the chemicals after washing the engine
This has been specified in Maintenance Manual for Arriel but not Makila and Arrius • Drying o Arriel engines have different engine running time for drying based on the type of Washing
Engine running – 30 seconds
Ventilation – 300 seconds o Makila and Arrius on the other hand have same engine running time for drying of 300 seconds

5.3.3 COMMENTS Listed below are some points and ambiguities in the procedure which might be confusing and can lead to an improper execution of the maintenance task: • Consumables o The products required for rinsing are not mentioned in consumables in procedures of Arrius 2B2 and Arriel 2S2 o Although, they are mentioned separately elsewhere in the procedure/Maintenance Manual • Soaking o CCT advises soaking of the engine with washing fluid for some time o But, in effect none of the engines’ Maintenance Manuals specify soaking of the engine with washing fluid • Arriel o Ambiguity in the table listing Percentage of washing mixture o Ambiguity in what is meant by double the quantity of anti-icing
Volume of anti-freeze product can be doubled
Percentage of anti-freeze product can be doubled o Ventilation time is given as 20 seconds ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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o

• •

This should be checked with starter generator limitation written in Aircraft Manual Note to “Start injection at 10% N1 and continue till it drops below 10% not written”. This should be included; otherwise there can be accumulation of cleaning products on the engine. Additional Procedures not mentioned

o Makila o Number of Ventilations should be specified more clearly Arrius o Number of Ventilations should be specified more clearly o Blanking of Aircraft Manufacturers Bleed not mentioned

5.3.4 WASHING PRODUCTS Washing helps in quick removal of corrosive effluents. To achieve this certain chemicals are required. These chemicals should be tested and approved by the engine manufacturer before use, since they might have negative effects on the engine. TURBOMECA qualified washing products are tabulated as follows: Cleaning product • Validated products (recommended)

•

Water quality

ARDROX 6367 (Turboclean 2)

TURCOJET WASH K3 •

Products authorized for use (replacement)

Anti-freeze product

ZOK 27

Isopropyl alcohol

Distilled water Demineralised water

TURCO 6783-50

Table 11: Washing Products For proper and effective washing, it is also imperative to have proper concentration of the washing product, based on the following table

T0

Anti-freeze product (*) % v/v

Cleaning product % v/v

Water % v/v

T0 ≥ 5°C (41°F)

0

2

98

18

2

80

33

2

65

5°C ≥ T0 ≥ -8°C (17.6°F) -8°C ≥ T0 ≥ -24°C (11.2°F)

Table 12: Proportion of Washing Mixture (*) If the methanol/water mixture is used, the proportions of anti-freeze product must be doubled. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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5.4

CLEANING

Cleaning process is done in order to remove dirt and dust particles, insects and oil which have entered into the engine air path with the help of a degreasing liquid. This task is usually required to be performed weekly, but special circumstances may increase the frequency of the operation. In contrast to Rinsing and Washing this task can only be performed with the dry crank (ventilation) and is more time-consuming. Nevertheless, it is the most effective of all he three tasks and can fully recover engine performance, hence, is also suggested in case of failure in Power Assurance Check (negative Torque or T4.5 margin).

5.4.1 GENERIC PROCEDURE The generic procedure for cleaning is listed below; it is different mainly in the fact that it can be performed during ventilation (with dry crank) and requires soaking of the cleaning mixture for a long period of time (~20 minutes). The procedure of cleaning is concluded by that of rinsing. •

• • •

• •

• •

Preparation of Rinsing mixture o Quantity of mixture o Percentage of Constituents ( Demineralised Water and Anti-Icing Agent) o Homogenization Aircraft Settings o Blanking of Bleed Valve o Closing all the aircraft manufacturer bleed valve Tool Settings o Connection of the tool o Pressure/Flow settings of the tool Injection of Rinsing Mixture o Cranking
Number of times
Amount of time
Flow speed o Engine Running
N1 specification
Amount of time
Flow Speed Soaking o Time of soaking o Required for proper cleaning of dirt Rinsing o Described in Sec 5.2 o Done after Cleaning o In order to remove cleaning product Removal of Equipment o Of tools o Of blanks on valves Drying of the engine o Time o Procedure o Exceptions

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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•

Post-maintenance Procedure o Internal Protection o External Protection

The factors listed in italics above are the specific numerical parameters which differ form engine to engine and are based on engine parameters.

5.4.2 DIFFERENCE BETWEEN ENGINES

Cleaning Mixture Quantity Consumables

Percentage

Arriel 2S2

Makila 2A

Arrius 2B2

Necessary Cleaning Product Demineralised Water Anti-Icer Mentioned - but does not add up to 100%

4 litre Cleaning Product Demineralised Water Anti-Icer

3.5 litre Not Mentioned

Substitute Products - % Not Mentioned

Homogenization

As per CCT_00800_C As per CCT_00800_C

Mentioned

Mentioned

Mentioned

Mentioned

Mentioned

Not Mentioned

100 °C Allowed – Ambiguity in MM

70 °C

70 °C

Not Allowed

Allowed

Not Mentioned Aircraft Based

Not Mentioned Present in Engine

Based on the Tool Present in Engine

2 10 minutes - twice Not Explicitly Written Not Listed in MM

One or More 20 minutes Yes Listed in MM

One or Two Nil Yes Listed in MM

300 Not listed

Not Explicitly Written Internal Protection External Protection

300 Internal Protection External Protection

Aircraft Settings

Manufacturer Air Bleeds Cooling T4.5 Ventilation Tools Settings Flow Speed Washing System Procedure (Only Cranking) Ventilations Soaking Time Rinsing Cranking Drying Time (seconds) Additional Provisions

Table 13: Comparison of Cleaning Procedure ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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The following differences occur in the procedures of the three engines: • Quantity of Rinsing Mixture o Is least for Arrius and highest for Makila depending on the size • Flow Speed o Not mentioned for Arriel and Makila engines hence cannot be compared • Drying of the Engine o Is 300 seconds for all three engines o For Makila engines it is not explicitly written • Cooling Temperature (T4.5) o Arriel engines need to be cooled to 100°C while th e Makila and the Arrius engines need to be cooled to 70°C • Cooling through Ventilation o Not allowed for Makila 2A o Allowed for Makila 1, Arriel and Arrius • Procedure for Cleaning o Number of ventilations are dependent on the Customer in Makila and Arrius o For Arriel, two ventilations are specified • Soaking o Two 10 minute soakings for Arriel Engine o One 20 minute soaking for Makila o No soaking specified for Arrius Next we list a few ambiguities present in the procedure and suggestions for the same.

5.4.3 COMMENTS Listed below are some comments about the procedure: • Makila o Quantity of Cleaning Product is 4 litres
This is quite less in comparison with rinsing and washing o Number of “Crankings”
Should be specified clearly in the Maintenance Manual o Drying of the engine
Not written explicitly in the Maintenance Manual
It is mentioned to Rinse the engine which also includes drying
Nevertheless, should be mentioned explicitly so as to avoid any confusion o Chapter on Cleaning Products – The clause “Refer to the specificities of the engine” should be removed • Arriel o Percentage of Cleaning Products
Mentioned percentage doesn’t add uo to 100 %
For Substitute Products (Replacement/approved products) the percentage of cleaning products are different as compared to Recommended Products – This has not been mentioned o Ambiguity/Mistake in a Note written about cooling the engine with ventilation
NOTE: For a T0 of 15°C (59°F), it takes 50 minutes to decrease the temperature to 100°C (212°F) or 25 minutes to decre ase the temperature to 100°C (212°F) if you do two ventilations of 30 seco nds, with 1 minute between them. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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•




Two values of time (25 min and 50 min) given for same procedure

Arrius o Not mentioned to close aircraft manufacturers bleed valve o The process described for cleaning starts with the heading of “Engine Protection” instead of “Engine Cleaning”

5.4.4 CLEANING PRODUCTS 5.4.4.1

DESIGNATION The products approved or authorized for cleaning of engines are tabulated below. As far as possible only recommended products must be used, only in rare cases replacement products should be used. Cleaning product • •

Validated products (recommended) •

Products authorized for use (replacement)

Anti-freeze product

Water quality

ARDROX 6367 (Turboclean 2) ARDROX 6368 ready to use (Turboclean 2 RTU) (**) TURCOJET WASH K3

•

ZOK 27(**)

•

RMC-G21(**)

• • • •

TURCO 4217 TURCO 5884 TURCO 6783 series ARDROX 6334

•

AL 333

•

SOLVEX ICE 113

•

SINCLAIR S (SOCOMOR)

Isopropyl alcohol

Pure methanol (AIR 3651) Methanol/water 44/56 or 50/50

Distilled water Demineralised water

Minimum quality of water

Table 14: Cleaning Products 5.4.4.2

PROPORTION OF THE MIXTURE For proper and effective washing, it is also imperative to have proper concentration of the washing product, based on the following table. It should be noted that for replacement products the percentages in cleaning mixture are different. Anti-freeze product (*) % v/v

T0

Cleaning product % v/v

Water % v/v

T0>5°C (41°F)

0

20

80

5°C>T0>-8°C (17.6°F)

15

20

65

20

50

-8°C> T0>-24°C (11.2°F)

30

Table 15: Proportion of Cleaning Mixture ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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The proportion of mixture for replacement products are listed as follows: •

For the replacement products : o Cleaning product at 50% v/v: SOLVEX ICE 113 o Cleaning product at 25% v/v: AL 333 o Cleaning product at 20%v/v: Turco 6783-50 o Cleaning product at 10% v/v: ARDROX 6334, Turco 6783-3 o Cleaning product at 15% v/v: SINCLAIR S o Cleaning product at 5% v/v: TURCO 4217, TURCO 5884 o Ready to use cleaning product: Turco 6783-10.

Following points should be further noted in regards to proportion of the mixture: • •

5.5

If the 44/56 or 50/50 methanol/water mixture is used, the proportions of anti-freeze product must be doubled (*) Some products are RTU (Ready To Use) and do not require any water (distilled or demineralised) (**) o This applies to ZOK 27 which also comes in a ready to use form: ZOK 27 RTU, Ardrox 6368 and RMC-G21, o The proportions of the product are therefore
100% of the product for T0>5°C,
15% anti-freeze + 85% product for 5°C>T0>-8°C and
30% anti-freeze + 70% product for -8°C> T0>-24°C.

FREQUENCY Frequency of performing operations of Cleaning, Washing and Rinsing highly depend on the surroundings and operating conditions of the engine. Hence, it is advised that the operators based on performance decide the frequency of these operations. The frequencies suggested in the Maintenance Manual are the least required for given operating conditions; they should be increased based on environment, on-condition monitoring and performance deterioration:

5.5.1 GENERAL CASES Operation

Saline or corrosive atmosphere

Polluted atmosphere

Daily (after the last flight of the day) Daily (after the last flight of the day) See engine specifications (Makila aero: weekly, etc.)

Daily (after the last flight of the day) See engine specifications (Makila aero: weekly, etc.)

Internal protection

Before engine storage

Before engine storage

External protection

Before engine storage weekly

Before engine storage

Rinsing Washing Cleaning

None

Table 16: Frequency of Cleaning Procedures in General Cases ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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5.5.2 SPECIFIC CASES 5.5.2.1

CLEANING • • • • •

Drop in performance Before 72-hour downtime At the start of periodic inspections Before engine storage After ingestion of foreign bodies.

WASHING OR CLEANING (ACCORDING TO CONDITION OF THE ENGINE)

5.5.2.2 • •

After use of extinguishers on a hot engine After use of extinguishers on a cold engine

Apart form the frequencies mentioned above, specialized cleaning procedure can be suggested for performance recovery of the engines.

5.6

TOOLS

Tools play a major part in cleaning, as they • Maintain the required flow speed. • Maintain the amount of fluid flow • Dictate the optimum droplet sizes of cleaning mixture • Provide correct path for flow of cleaning mixture Hence, for proper cleaning, it is mandatory that only Turbomeca approved tools at specified settings are used. Furthermore, the Tools (specifically Pressure Generator) should be checked and inspected regularly with specific equipment that whether they are providing required performance or not. The following table lists the Tools (with their respective part numbers) required for cleaning, washing and rinsing operations:

Arriel 2S2 OT 20 0010 TM0188G002

Makila 2A OT 71 0050 8818480000

Arrius 2B2 OT 0057 TM0188G001

Compressor Washing Unit

N.A.

Attached to Engine

Attached to Engine

Equipped Flow Limiter

OT 20 0020 8819505000

N.A.

N.A.

Bleed valve Blanking union

OT 20 0030 8816517000

N.A.

N.A.

Pressure Generator Tank

Table 17: List of Required Tools Few tools are required for cleaning, washing and rinsing of engines which include: ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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•

Spray Equipment o Pressure Generator Tank o Nozzle o Below is the table of various parts that are present in a generic Pressure Generator Tank (The Symbols correspond to the illustration provided in Figure X)

Figure 8: Pressure Generator

• • •

Table 18: Pressure Generator, Arriel 2S2

Flow Limiter o To limit the flow rate of cleaning mixture from the pressure generator tank Bleed Valve Blanking Union o To close the flap of bleed valve when connected to an external air supply Compressor Washing Unit o Dictates the flow path of cleaning mixture o Usually has a quick connect option where nozzle pipe from pressure generator can be connected, and cleaning can be carried out easily o Provides an optimum path for flow of the cleaning mixture

Figure 9: Compressor Washing Unit for Makila 2A ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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5.7

PRODUCTS USED The products pertaining to each of the operations have been already listed with the respective processes. Here, we give an overview of the same. The products used for Cleaning, Washing and Rinsing are divided into two categories: • Validated products: products validated by the CVI that can be used in rinsing, washing, cleaning and protection operations. • Products authorized for use: products authorized by the CVI for use if the validated products cannot be used. The CVI is abbreviation for Consumable Validation Committee which validates and authorizes the chemical products which can be used for Cleaning, Washing and Rinsing. Without its approval, use of chemicals is not allowed. While using the products, proper care must be taken to protect self and the engine. Also, the percentages of product should be correctly and properly added, doing otherwise might lead to negative effects. Some products, especially the Ready-to-Use products and Replacement products are required to be added in different percentages. The ambient temperature also influences the concentration of the products. As various Chemical products are recommended and approved it is the choice of the operator to choose one from them. Though, Turbomeca makes no distinction between the recommended cleaning products following parameters can be used while choosing the most-suited product by a helicopter operator: • Cost o Of Purchasing o Of Disposal • Availability o Based on region • Effectiveness o Based on previous experience • Environmental Friendly • Boiling Point o Higher boiling point of product is advantageous for cleaning o Since, the engine temperature rises very rapidly once it is turned on – it may cause evaporation of the cleaning mixture o This can result in an incomplete or ineffective cleaning While estimating the cost of cleaning product the cost of disposal should also be accounted for. If the cleaning product is environmental friendly the cost of disposal will be lesser, and hence it is advantageous to have the same. Also while choosing the cleaning products amount of surfactants and boiling point of the cleaning product is an important factor. It is better to have cleaning mixture with higher boiling point for proper cleaning. If the boiling point of cleaning mixture it shall evaporate very quickly once the engine is started and will not be able to cool aft stages of compressor and turbine. Apart from chemicals the primary consumable required for engine cleaning is water. The quality of water is very important, and hence only recommended or approved water should be used. The Validated (recommended) water quality for use is that of:

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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•

•

Distilled Water o Appearance: clear, limpid, colourless, with no deposits or materials in suspension o Conductivity at 25°C : 5 µS/cm maximum o pH: 5 – 7.5 Demineralised water o Appearance: clear, limpid, colourless, with no deposits or materials in suspension. o Conductivity at 25°C : 10 µS/cm maximum. o pH: 5 – 7.5.

The Authorised (replacement) water quality for use is listed below. It should be used only in rare and exceptional circumstances. The characteristics required for replacement water are as follows: •

Minimum Quality Water o Appearance: clear, limpid, colourless, with no deposits or materials in suspension o Particles remaining after evaporation at 110°C: ma ximum of 175 ppm o Chloride content: 15 ppm maximum o Sulphate content: 10 ppm maximum o Sodium content: 10 ppm maximum o Conductivity at 25°C (optional): 400 µS/cm maximum o pH: 6 – 8.5. o Hardness: 18°F maximum Note: 1°F = 4 ppm of Ca 2+ = 2.4 ppm of Mg 2+ = 10 ppm of CaCO3

Irrespective of the supply source of this water, the above conditions must be guaranteed over time. The criteria specified for inspection of quality of water is based on ISO 3696 standards, and they should be referred in case of any confusion. The risk of contamination increases from distilled water to demineralised water and becomes significant if the minimum quality of water is used. Nevertheless, it remains acceptable if the water quality criteria are met. If the water properties are sub-standard the water instead of cleaning can cause various deposits and contamination of the engine. Following problems can occur in case minimum water quality is not met: • Blocking of the combustion chamber, which obstructs the air accesses in the chamber and causes poor combustion, • Presence of deposits on the turbine blade, which become coked during use and cause a change in flow, • Corrosion of the turbines and compressors caused by too great a quantity of chloride, sulphate and alkaline ions in the liquid, • Corrosion of the compressors and the bearings by stagnant water if the drying is poorly carried out. Finally, it should be duly noted that the tap or drinking water should not be used for Engine cleaning purposes. Drinking water is a definition that deals with food hygiene and is not same as the criteria required for rinsing, washing or cleaning operations. It may contain large quantities of minerals (chlorides, sulphates, sodium, etc.) that can corrode or lay deposits on the engine. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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5.8

CAUTIONS - HEALTH, SAFETY, ENVIRONMENT While doing any type of maintenance, let alone Cleaning, Washing and Rinsing proper care must be taken to product oneself as well as the engine. Due to the use of chemicals it is necessary that proper equipment is used and care taken while doing operations of engine cleaning. Following must be specially noted:

Health and safety of the Operators: • • • •

Do not breathe in cleaning product vapours. Work in a well-ventilated area. Never let the cleaning or protection products come into contact with the skin. Protect the hands with synthetic rubber gloves and the face with a screen or goggles.

Cleaning and protection products can be toxic, refer to the safety data sheets for the products used and implement the necessary precautions (wearing PPE, suitable storage conditions, etc.). Consult the supplier for any problems with or questions about the products.

Care of the Engines • • • • •

Use only distilled or demineralised water Use the recommended cleaning products. Other cleaning products cannot be used without the agreement of TURBOMECA. Likewise, use the recommended anti-freeze products. Other anti-freeze products cannot be used without the agreement of TURBOMECA. The supply time of Starter –generator should comply with limitations provided in Aircraft Flight Manual For treatments carried out during ventilation, ensure that the temperature T4.5 is less than or equal to 70°C for Makila and Arrius, and 100°C f or Arriel.

Notes for proper Cleaning •

• • • •

Cleaning Mixture • The mixture should be properly homogenized before use • Proper percentages of chemicals should be added based on ambient temperature and data provided in Maintenance Manual • While using Ready-to-Use products care should be taken of not to mix them with water Air Path • All the valves which could be affected should be closed • Aircraft manufactures valves should be blanked As far as possible Cleaning should be done with Ventilation (Dry Crank) Standard practices provided in Maintenance Manuals should be followed Value of N1 should be monitored • Injection should be started only when N1 reaches above 10% • Injection should be stopped when N1 reaches below 10% • While engine running N1 should not drop by more than 10% • Prevents accumulation of cleaning product and • Ensures proper action of cleaning mixture

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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6 CLEANING, WASHING AND RINSING – CUSTOMER STUDIES Maintenance of engines due to variety of reasons, at times, might not be as “smooth” as desired and both Customers and the Service Providers have to work together in order to find out the solution and eliminate the problem. The problems in maintenance might appear due to either discrepancies in the Maintenance procedures (ambiguities or errors in Maintenance Manuals) or due to negligence on the Customer’s side (usage of incorrect tools, unqualified material) or due to extraneous factors (such as environmental conditions). To maintain the quality of the Maintenance and Support and avoid such undesirable circumstances, various measures are adopted which include • Proper and timely Training of Customer and Maintenance Engineers • On-site Field Representative from the OEM to monitor the maintenance and for troubleshooting • Interaction of Customers(Engine Users) and Engineers(Designers and Manufacturers) for proper communication of requirements and problems through Symposiums • Continuous validation and verification of all the maintenance documents, specifically those related to 1st Line Maintenance • Improvement and simplification of the maintenance procedures to the best extent possible without compromising the primary goal of safe and accurate maintenance In the past, there have been times where the procedures specified for Engine Cleaning have to be monitored, modified and tailored specific to the customer in order to eliminate problems associated with Engine Cleaning and for proper Performance Recovery. Some such studies are described in this section.

Figure 10: Evolution of Procedure through Troubleshooting When, such problems arise the engine user reports the problem to the Support department through the respective Field Representative. First, an attempt to troubleshoot the problem on-site is made without affecting the operations of the customer by monitoring the procedure, tools and equipments. If this does not yield solutions, detailed studies are carried out by Field Representatives and Service Engineers which might require some engines to be grounded. Based on the finding of the studies, solutions are proposed which might be in the form of explanation and corrections of mistake in maintenance procedures which the customer might be unknowingly making OR specifying Customer tailored maintenance procedures usually due to the environmental conditions or the operating regime of the Customer’s fleet. The solutions proposed are monitored for sufficient period in order to ensure that the problem is solved. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Figure 11: Evolution of Procedure through Customer Experience Also at times based on experience as well as operating conditions, Customers evolve the procedures, making them better and cost-efficient. Such betterments in procedures before being formalized and used need to be authorized and verified by the Engine manufacturer. This also requires analysis by the Field Representatives and Service Engineers and results in modified, better and customer-tailored maintenance procedures. The customer studies are mentioned according to the regions that they were encountered in.

6.1

AUSTRALIA

6.1.1 Problem Operating conditions in Australia consists of sandy atmosphere and hence require effective cleaning of engine air path for Performance Recovery and functioning of the engine. One customer based on the experience with maintenance of engines suggested a cleaning procedure specific to such operating conditions. The following changes in the existing procedure were suggested by the customer for Makila 2A • Changes in frequency o Cleaning every second day o Reason: Operating Conditions • Changes in Cleaning Procedure o Inject mixture during a 5 second crank o Stop crank but continue to inject mixture for a further of 15 seconds, while the engine decelerates o Reason: Customer believed due to cranking air flow was high enough to cause the cleaning agent to go straight through the engine air path without proper cleaning

6.1.2 Analysis In order to formalize and use the modified procedure the Customer has to obtain authorization from the Engine Manufacturer, specifically, a letter of No-Technical Objection. While investing the modified procedure to issue the letter of No-Technical Objection following conclusions were drawn: ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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• •

Insufficient Crank Time o Result in inferior mass flow than required o Improper circulation of Cleaning Fluid Accumulation of Cleaning Product possible o Accumulation around axial compressor labyrinth seals o Possibility of Corrosion o Possibility of cleaning mixture being mixed with oil system

6.1.3 Solution Based on the above-mentioned analysis and discussion with the Customer a modified version for Cleaning was suggested, which was later adopted by the customer. The changes made were as follows: • Changes in frequency o Cleaning every second day • Changes in Cleaning Procedure o Begin Cranking and allow N1 to reach 10% (approximately 7-10 seconds) o Once, N1 reaches 10% begin injection of Cleaning Mixture o Continue cranking for further 5 minutes and release crank button o After crank button is released, allow injection of mixture to continue for a further 10 seconds while engine decelerates o Allow to Soak for 20 minutes o Rinse air path by cranking and Carry out drying of the engine It can be seen that some of the suggestions made by customer have been retained whilst some new modifications are introduced in the procedure by the Service Engineer. Thus, by working together the Customer and the Engine Manufacturer can evolve the existing procedure into better procedures, as was observed in the this case. Customer’s experience might lead to some solutions which are worthwhile for short-term but may have major longterm effects. Hence, only after proper analysis and approval of the Engine Manufacturer, a new procedure should be adopted for use.

6.2

NORTH AMERICA

6.2.1 Problem In North America region one of the operators reported problems with respect to performance of its Arriel 2S1 and 2S2 engines, which subsequently required unscheduled removal and deep-maintenance of several engines of its fleet. On probing, it was observed that the maintenance of the engines was not up-to the mark; hence, a modified and stringent Cleaning procedure coupled with Engine Performance Check was specified for the helicopter operator.

6.2.2 Analysis As mentioned earlier various engines had to be removed from the fleet, which was mainly due to improper and untimely maintenance of the engines. It was decided to monitor the Engine Performance Check (EPC) data to identify any further problems in maintenance of engines. A modified, more stringent cleaning program was specified as well. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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6.2.3 Solution In order to make the procedure more stringent and foolproof following points were added in addition to Maintenance Manual: • Engine cooling suggested to 100 °F ( ~40 °C), inst ead of 70 °C • An additional soaking of 5 minutes advised during washing • Further, the quality of water and periodicity of cleaning operations were asked to be strictly respected. The modified versions of Engine Washing and Cleaning suggested were as follows: • Frequency o Engine wash - Daily o Engine cleaning - Weekly • Modified procedure for washing o Let the engine cool to 100 °F o Washing Mixture – ZOK 27 at 12% mix with purified water o Ventilate with an APU (cranking) for 15 seconds while injecting the mixture o Soak for 5 minutes o Do a dry 15 second APU ventilation to expel any remaining fluid • Modified procedure for cleaning o Let the engine cool to 100 °F o Cleaning Mixture – TM approved cleaning liquid at 20% mix with purified (demineralised/distilled) water o Ventilate with an APU (cranking) for 15-20 seconds until the mixture comes out of the tail pipe o Soak for 15-20 minutes o Rinse with purified water for 15 seconds each ventilation until clear water is expelled from the engine o Perform a ground run to dry the engine Also, continuous monitoring of the Engine Performance Check (EPC) Data was done to check the effectiveness of the solution and avoid any further problems.

6.3

NORTH SEA

6.3.1 Problem Several helicopter operators work in the North Sea region as a lot of helicopters are required for the operations of extensive Oil and Gas industry North Sea houses. Due to the chemically corrosive atmosphere, engine cleaning is of utmost importance. One of the helicopter operators reported problems with maintenance and performance of engines which were traced back to problem with engine cleaning.

6.3.2 Analysis A survey was carried out by the Field Representative located at the North Sea region of cleaning practices of four different operators (including Operator “B” which had problems with Engine Cleaning): ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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RINSING Frequency Water Fluid Injection Quantity Time

A B C D EDF EDF EDF EDF Demineralised Demineralised Demineralised Mains Water Engine Running Engine Running Engine Running Engine Running Compressor Compressor Compressor LANCE Washing Kit Washing Kit Washing Kit 3½ litres Per MM Per MM Per MM Per MM Per MM Per MM Per MM

Table 19: Survey of Rinsing of North Sea Operators Most of the quantities listed above though different are approved by the Maintenance Manual. The main differences were: • Quality of Water o Mains Water (Minimum Quality Water) used by Operator D o As much as possible Distilled or Demineralised water should be used • Quantity of Rinsing Mixture o 3.5 litres for Operator A o Maintenance Manuals though does not require to use any specific quantity suggests usage of around 6 litres of water

CLEANING Frequency

75hrs

Water Product Name % Quantity Period

Mains Water

Winter EPC Failure Cleaning before maintenance

75hrs

Demineralised RMC G 21 Ardrox 6376 ( Ready Mixed ) Not Known 5% Per MM Per MM Per MM Per MM Heated Isopropanol mix Demineralised water Cleaning then Rinse followed Washing by cleaning No

Occasionally

75 hrs OR 15 days (whichever is minimum) Demineralised

Mains water

Ardrox 6376

Ardrox 6376

20% Per MM Per MM

20% Per MM Per MM

Methanol Mix

Methanol mix

Rinse followed by cleaning

Cleaning

If aligned with 75hrs

Occasionally

75hrs

Table 20: Survey of Cleaning of North Sea Operators

6.3.3 Solution Although there were several parameters which differed in between the operators, most of them were those approved by the Maintenance Manual. In spite using “Mains Water” (Minimum Quality Water) many operators still didn’t face any problems (This doesn’t mean quality of water is not of consequence. For proper cleaning only demineralised or distilled water should be used). ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Operator “B” who was suffering from problems had one main difference and that was the use of Ready-to-Use Cleaning Product. It was concluded on further investigation that some mistake was being made in proportion (percentage) of Cleaning Product in the Cleaning Mixture. The use of Ready-to-Use Cleaning Products (such as ZOK 27 RTU, Ardrox 6368 and RMC-G21) doesn’t require mixing of any water. After indicating this correction in formation of cleaning mixture, the cleaning of engines was monitored and no further problem was observed. In this analysis, we saw there were several parameters which were different between the four operators – indicating the flexibility and robustness of the current procedure – which made the diagnosis of the problem difficult. Yet, based on basic engineering know-how, and admittedly with some trial-and-error, it was possible to identify and rectify the problem. Also, operators which were using Mains Water (and were still not suffering from any problem) were advised to use Distilled or Demineralised water in order to avoid any problems in the future.

6.4

ASIA PACIFIC

6.4.1 Problem With this Engine Operator, too, problems were first observed during Power Assurance Check which showed decline in performance of fleet of Arriel 2S2 engines. While doing further analysis and on-condition monitoring presence of white deposit was observed in Module 03 (Centrifugal Compressor, Combustion Chamber and Nozzle Guide Vanes of Gas Generator turbines).

6.4.2 Analysis Analysis and Trouble-shooting of the problem was done by the Service Engineers and presence of white deposit was detected in the engine. It was concluded that this might be due to Excessive ingestion of Cleaning Product/Mixture OR Quality of Water. Initially, while the analysis was being done as an interim solution it was suggested to increase the frequency of engine cleaning. After the full analysis the following personalised cleaning procedure was suggested for engine cleaning operation.

6.4.3 Solution The changes made were as follows: • Changes in frequency - Cleaning every 50 hours or a week (whichever is minimum) • Changes in Cleaning Procedure o Quantity of Mixture – 2 litres
As opposed to necessary in maintenance Manual
Ambiguity was eliminated o Changes in Flow Injection and Soaking
Only 1 flow injection in place of two
Amount of soaking time – 20 minutes o Additional Rinsing Procedure required to be done at the end of cleaning
To eliminate accumulation of cleaning product ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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•

Additional Suggestion o Strict compliance with quality of water was demanded
Use of only distilled or demineralised water o Trend monitoring of engine was suggested o

After suggestion of this procedure, problems were still observed. These were attributed to quality of water. One month after the above changes were suggested some more clarifications and modifications in the form of a “Technical Memo” were introduced in order to eliminate the problem: • Clarifications in Cleaning Procedure o Every 50 hours o Flow injection during ventilation of 20 seconds (2 to 3 litres/min) o Soaking Time – 15 minutes o Two Rinsing Operations each of 15 second ventilations o After removal of tools the Drying of engine ; by running engine for 5 minutes • Performance Recovery Programme o In case of negative Torque or Temperature Margin during ground run o If negative margins are encountered in flight, first a ground Power Assurance Check must be done for the margins o Application of Modified Cleaning Procedure (specified above) daily once for next 5 consecutive days of operation • Reminder about initiation and continuance of Performance Trending Programme to predict and avoid future problems • Reminder about Quality of Water • Checking of Cleaning Tools o Checking of flow rate provided o Every two months

6.5

SUMMARY We saw a variety of problems could occur due to cleaning if procedures are not followed properly or at times due to the operating conditions. The main cause though usually is • Quality of Water • Improper concentration of Cleaning/Washing Product • Improper implementation of Procedure • Operating Conditions Problems of the nature that we saw above are inevitable due to human factors, and require quickwitted thinking and problem solving skills from the Field representative and the Service Engineer. The solutions found have to be practical in nature and need to be arrived quickly. Support from customers by quick implementation of suggestions is highly effective, and should be ensured. Proper care has also to be taken to minimise the trouble caused to the customer. The engine down time is to be reduced to the barest minimum, so that operations of the customer are not affected. Monitoring and validation of solutions suggested is always to be done so as to avoid any side effects. This can be very difficult at times but can be facilitated by proper analysis and proper education of operators for Maintenance Procedures through timely training and continual communication through Symposiums and Forums. The experience of customer is also very valuable, as we saw in the first case, and can often lead to improvement and evolution of existing procedures.

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7 CLEANING, WASHING AND RINSING – EXPERIENCES OUTSIDE TURBOMECA In the previous sections we saw the introduction and detailed analysis of Cleaning, Washing and Rinsing specified by Turbomeca specifically for its Turboshaft Engines (Arrius, Arriel and Makila). Next, we saw the evolution of these specific procedures due to problems and experiences shared by the Helicopter Operators. This section now gives an overview and analysis of procedures and studies regarding cleaning of engines available and adopted outside Turbomeca. This section is derived from the open literature and publications available on Cleaning of Turboshaft Engines. Hence, in contrast to the previous sections it is far more generic and we shall not be considering the semantics (wordings) and minute details of the processes as was done before. Rather, here we give an overview of current state-of-the-art of Engine Cleaning based on previous experiences and studies. Firstly, to be on an equal footing nomenclature described earlier with the jargon used in the studies and publications. Thereafter, evolution of cleaning procedures over the years is discussed. Lastly, a few comments and suggestions based on analysis of these publications for design of better cleaning procedures are compiled.

7.1

NOMENCLATURE The terminology used till now was specific to the turboshaft engines of Turbomeca. In open literature the jargon is slightly different and in order to compare the external procedures with that discussed earlier, we go through the definition of the terms used. Usually, studies are found about engine Washing or Cleaning, and Rinsing is very rarely mentioned. This is because “Rinsing” almost always in integral part of the cleaning/washing procedure. In publications, the term “Washing” is often used to mean washing only with water, while “Cleaning” refers to cleaning of engine with specified chemical products. To avoid confusion and maintain uniformity the term “Washing with only water” shall be used in this document. Based on the type of cleaning, it is classified as follows:

On-Line Hot Engine Running •

•

Off-Line Cold Dry Crank/ Ventilation

Table 21: Terminology for Engine Cleaning Online Cleaning – o Is same as cleaning during Engine Running; and o Is often referred to as a hot wash Offline Cleaning – o Is same as cleaning during Ventilation (using the dry crank); and o Is also called cold wash

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7.2

LITERATURE SURVEY Open literature and publications tell a lot about the current state of affairs and proceedings of the respective field. They can provide details of the previous problems faced and solutions found with regards to evolution of the process. In this section we discuss the evolution of Engine Cleaning based on data available in open literature. The references and publications used for compiling this section are rich and extensive resources for information on Engine Cleaning and can be referred for further information. In the next section, application of this information onto helicopter turboshaft engines based on comparative analysis is presented.

7.2.1 INTRODUCTION Interaction of particles in the air flow with engine components, results in fouling of airfoils and annulus surfaces, which causes changes in shape and roughness of compressor section. This leads to: • Reduced Efficiency • Reduced Pressure Ratio • Reduced Power Output • Reduced Stall Margin Typically, 70-85% of the overall performance loss during operation can be attributed to compressor fouling. Furthermore, without timely maintenance, fouling leads to permanent damage to compressor and other engine parts, rendering engine removal inevitable. Thus, we can quite clearly see how important Engine Cleaning is in terms of both time and money. Experiments have shown that, on an average, proper Cleaning of the air path can recover over 98% of the lost performance.

7.2.2 EVOLUTION Several methods were adopted in the past to clean the Gas Turbine Compressors and depending on their characteristics have evolved over time. The most obvious and also the most effective way is to manually clean the compressor using brushes and detergents. However, this requires engine to be cooled, shutdown and disassembled and is very laborious as well as time consuming. Thus, although very effective it is used only in extreme cases. The next method to be developed was "abrasive grit-blasting" which required injection of abrasives like charcoal, rice, nutshells or synthetic resins into the airstream of the operating engine. Literature reports satisfactory cleaning results except for cleaning of oily deposits especially in the aft stages of the compressor. Being a simple and fast method without downtime it was used widely in the 1970s, and was modified with various improvements to avoid the contamination of internal passages and clogging of cooling holes. However, in 1980s with the introduction of protective blade coatings and due to the risk of erosion by impact of particles this practice slowly disappeared on account of potential damage. This method is not suited for the state-of-theart turboshaft engines that are used today. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Method Manual Cleaning

Materials Brushes Washing agent

Advantages

Disadvantages Shut down of engines

Very effective

Dismantling of engines Requires extensive man power Less effective at rear stages and for oily deposits Clogging of internal cooling passages Erosion Increased surfaces roughness

Rice Simple and fast Grit Blasting/ Abrasive Cleaning

Soak, crank, offline washing Fired, online washing

Charcoal Nut Shells Or Synthetic Resins Demineralised water, Chemicals Demineralised water, Chemicals

No engine downtime Effective in cold environments

Damage of blade coatings

Very effective

Shutdown of engine

Low interference with engine operation

Less effective Cannot replace offline washing

Table 22: Evolution of Engine Cleaning Procedures A milder method hence was developed, to wash off the deposits using water with and without the addition of chemicals, detergents and/or surfactants. This was found to be more effective than the abrasive cleaning methods and has become the leading applied method. It is further divided into two methods, namely, offline and online. As explained earlier the cleaning depending on the use of detergent (cleaning product) is known either as cleaning, washing or rinsing. The soak or crank wash, also referred to as offline compressor wash, requires a shutdown of the engine and is performed using dry crank, with the starter motor turning the engine. The rotational speed is therefore on the order of 20% to a maximum of 30% of the normal operational speed, resulting in a reduced airflow through the engine. The only disadvantage of this method is the shutting down of engines and the extensive time required; this includes the time required to • Cool the engine o Time required may be up to 3 hours for helicopter engines
As they are light weight and with relatively low metal content o For land engines the time for cooling is usually even higher • Injection of Cleaning Fluid at reduced speed o Hence for more time as compared to online washing • Soak the cleaning product o For proper effect of cleaning products and surfactants • Rinse the engines o To remove accumulation of chemicals • Dry the engines o To prevent corrosion ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Figure 12: Compressor Washing System Now it’s the leading method applied to aircraft and helicopter engines, but initially concerns were raised on its effectiveness and the problems of corrosion it might cause. It is used in combination with online wash (with engine running) to give effective as well as timeefficient procedures.

7.3

SUMMARY The following table summarises the comparison of various parameters of this method for several gas turbine engines. This data was gathered from open literature and is not broad enough to draw conclusions regarding cleaning. More data (specifically of helicopter engines) can be collected in order to validate cleaning parameters for Turbomeca Engines.

Engine Manufacturer Type Turbomeca Turboshaft Marine Lycoming Turboshaft Rolls Royce Turbojet GE

Turbofan

Rolls Royce

Turbofan

Siemens

Land Gas Turbine

Air to Compressor Dry Power Airflow Liquid Pressure Fluid Stages Mass ratio MW kg/s litres litre/sec M Pa kg 2,65 2 7 0,05 0,7 4 279 Fluid Rate

Name Makila TF 40 B

13

80

11

0,091

135

-

-

602

Avon LM 2500\CF 6 RB 211 24G

14

75

265

0,482

162

0,2

15

1300

25

68

76

0,367

189

-

17

4100

29,5

92

90-180

0,5

184

7

13

4360

260

620

300

0,833

787

5

15

-

V94.3 A

Table 23: Comparison of Engine Cleaning across various manufacturers Detailed studies on evolution and influential parameters exist in open literature (and are listed in References). Optimizing engine cleaning is highly specific to the particular engine type and can be done only by detailed theoretical or experimental analysis. However, the thumb rules obtained from literature are particularly useful in making quick decisions (specifically required in maintenance and support) and also for verification of existing procedures. With the same philosophy, based on data available from open literature, we now proceed to analyse and propose solutions for the problem of volcanic ash. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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8 VOLCANIC ASH - INTRODUCTION Since time immemorial, volcanoes have been considered as one of the most formidable phenomenon manifested by the Nature. Some theories even indicate that the extinction of dinosaurs could have been aftermath of certain volcanic eruptions. To this day, volcanic eruptions result in mass disruption of life and there is nothing that can be done to control these eruptions. However, by proper prediction and management the damage caused by an eruption can be minimized. Volcanic eruptions affect the environment through various channels which include Volcanic Ash, Lahars, Landslides, Lava and Tephra. Of all these effects, Volcanic Ash is the one that concerns aviation and only it shall be considered in this section. This section, like the previous one, is based on open literature and publications, available on Volcanic Ash and its interaction with Aviation and specifically engines. Firstly, basics about volcanoes and volcanic ash are presented. Then, the effect of volcanic ash on aviation in general is described. This section provides the background information for analysis and treatment of engine maintenance after encounter with volcanic ash, which is presented in the next chapter.

8.1

FUNDAMENTALS

This section describes the basic background of volcanoes, volcanic eruptions and volcanic ash; which shall be useful for the analysis of cleaning of engines affected by volcanic ash.

8.1.1 VOLCANOES Volcanoes in lay man’s terms are mountains that spill fire. Though one is not usually aware with the amount or the frequency at which they eject this so-called “fire”. Definitions of “Volcano” range from individual vents, measured in meters, through volcanic edifices measured in kilometres or tens of kilometres, to volcanic fields measured in hundreds of kilometres. Volcanoes though most of them are quite visible and are similar to mountains, but at times can be hideous and hard to differentiate from surrounding geology. Furthermore, due to the rare nature of their eruptions, some volcanoes may remain dormant for a very long period and not cause any explosion. Volcanoes, similar to mountains, can also exist in oceans, fully or partially submerged in water. The volcanoes are distributed across the globe, though there are some regions where their density is markedly higher. The densest region, which also affects aviation, is the famously known “Ring of Fire” which is distributed across the whole of Pacific, spanning Australasia, Japan and west coasts of North and South America. At any moment of time, including now, around 20 Volcanoes are erupting around the world. The number of volcanic eruptions depends on the time period considered, but on an average around 50-70 volcanoes erupt every year, and around 160 volcanoes are active every decade. The duration of a single eruption can be very short or very long, with volcanoes erupting continuously for decades, hence making it difficult to count and objectively define active volcanoes. In the past 10000 years there have been around 1300 volcanic eruptions of varying durations.

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8.1.2 VOLCANIC ERUPTIONS The arrival of volcanic products at the surface of the Earth is termed as an eruption. Some definitions of the word include purely gaseous expulsions, but it is usually confined to events that involve at least the explosive ejection of fragmental material or the effusion of liquid lava. This is done in order to record and categorize the eruptions so that they can be used for practical purposes. The volcanic eruptions are classified based on various metrics which are explained hereafter. Various metrics exist indicating the severity of the Volcanic Explosion depending on the volume of injected tephra, height of the ejected column, duration for which the eruption lasted, and so on. For aviation purposes the property used is “explosivity “. Explosivity provides some idea of the magnitude of the eruption and more important whether, and how much, volcanic ash is ejected into the atmosphere and also the likely height of the column. The quantitative metric to represent “explosivity” is known as “Volcanic Explosivity Index” (VEI) which depends on a rough estimate of the ejected mass, height of the volcanic ash column and duration of continuous eruption blast. The following figure shows the details about VEI. Due to the very nature of the volcanic eruptions it is quite difficult to classify them into rigid compartments and hence very criteria overlap.

Figure 13: Volcanic Explosivity lndex – VEI Aviation is specifically affected by the Plinian-type eruptions because they eject vast quantity of ash up to, and above, the cruising level of international jet transport. Having said this, however, it must also be emphasized that volcanic eruptions of lower VEI than Plinian cannot be totally ignored because of the ash column could reach jet cruising levels and, if the volcano is situated near approach/departure paths, even weaker columns could affect aircraft descending to or climbing from aerodromes. Also, since our main focus is on Helicopters, who fly at relatively low altitudes, are always more likely to be affected by explosions of lower VEI as compared to jet aircrafts. Helicopters, thus, can be affected by all explosions with VEI more than or equal to 2. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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8.1.3 VOLCANIC ASH Small jagged pieces of rocks, minerals, and volcanic glass the size of sand and silt (less than 2 millimetres in diameter) erupted by a volcano are called volcanic ash. Very small ash particles can have diameters lesser than 1 micrometre. Volcanic Ash, by its name can be misleading, for it is not the product of combustion, like the fluffy soft material created by burning wood, leaves, or paper. Rather, volcanic ash is • Hard, • Does not dissolve in water • Extremely Abrasive • Mildly Corrosive, and • Conducts electricity when wet Volcanic ash is formed during explosive volcanic eruptions. Explosive eruptions occur when gases dissolved in molten rock (magma) expand and escape violently into the air, and also when water is heated by magma and abruptly flashes into steam. The force of the escaping gas violently shatters solid rocks. Expanding gas also shreds magma and blasts it into the air, where it solidifies into fragments of volcanic rock and glass. Once in air, wind can blow ash particles tens to thousands of kilometres away from the volcano.

Figure 14: Scanning Electron Microscopy (SEM) Image of Volcanic Ash Deposit 8.1.3.1

CONSTITUENTS The composition of volcanic ash clouds, is dependent on the underlying magma, and so varies from one volcano to another. Generally it consists of • Silica (>50 %) o In the form of glassy silicates - Resembles sharp-edged glass shards o Is very hard, with hardness level of 6 on the Mohs’ Scale (similar to that of a pen-knife) - Has some amount of quartz making it very abrasive o Melting point of around (~1,100°C) • Smaller amounts of the oxides of o Primarily - Aluminium, Iron, Calcium and Sodium o And several other minerals in small quantities • Various Gases o Water vapour, Sulphur dioxide, Chlorine are main constituents The proportion of each of these gases varies o Hydrogen sulphide and oxides of nitrogen

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o o

8.1.3.2

These gases can combine to form acids which is harmful for engines Help in detection of volcanic ash clouds through satellites and causes electric phenomenon ( St. Elmo’s fire – similar to electrostatic discharge)

PROPERTIES Various properties of volcanic ash clouds are described as follows: • Size of Ash Particles o Depends on the explosion o Ash clouds have particles with diameters less than 2 millimetres o Smallest particles can have diameters lesser than 1 micrometre o This makes air intake filters ineffective • Density o For dry ash density ranges from 500 and 1500 kg/m3 o For wet ash density ranges from 1000 to 2000 kg/m3 • Hardness o Up to level 7 in Mohs’ scale of Hardness o Makes ash very abrasive • Conductivity o Only when ash is wet • Mass Loading o It is the concentration of volcanic ash following an atmosphere o Depends on prevalent conditions of the wind and the altitude o Used to decide whether the region is suitable (free from ash concentration) for safe flight or not • Height of Explosive Column o Depends on the explosion and VEI o Similar to Mass Loading is used to decide whether eruption is critical for aviation or not

8.2

VOLCANIC ASH AND AVIATION

The first major threat to aviation by the volcanic ash took place in the year 1982, when ash due to Mount Galunggung, a volcano in Indonesia, led to mid-air shut down of all four engines of a Boeing 747. Detailed studies have been carried out by various agencies, and has led to a community of volcanologist, geologists and aviation experts working together in order to mitigate any damage by volcanic ash. One may say the efforts have been successful to date, as no casualties have occurred in aviation due to volcanic ash. Quite recently, in April 2010, the aviation community was again majorly affected by the explosion of an Icelandic volcano, Eyjafjallajokull. This study was motivated by the need to define maintenance procedures for helicopter engines affected by volcanic ash, as an aftermath of the Eyjafjalljokull eruptions. This section describes effect of Volcanic Ash on aviation, and efforts made by various agencies to combat the same.

8.2.1 BACKGROUND Mt. Galunggung eruption (with VEI of 4) in 1982 first focused the attention of the aviation community on the volcanic ash. As indicated above, various eruptions, thereafter, have ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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created problems in operations related to aviation. Between 1980 and 2004 more than 100 jet aircrafts have sustained at least some damage after flying through volcanic ash clouds. Fortunately, no lives have been lost but monetary damages have been to the tune of billions. At least seven of these encounters have resulted in temporary mid-air engine failure. Engine failures have occurred at distances from 150 to 600 miles away from the site of eruption indicating the span of volcanic ash. Several studies have been carried out over the effects of these eruptions on aviation, and specifically in more detail on the effect of eruptions of Mt. Redoubt, Mt. Pinatubo, and Various Eruptions in Alaska. International Civil Aviation Organization, OACI, with the help of several agencies and meteorologist, volcanologist, and its own resources has developed volcano watch centres across the globe in order to spot and report eruptions to the aviation community. This has been helpful as well as necessary, since no reliable methods exist to predict the explosion or extent thereof. These volcano watch centres are formally known as VAAC (Volcanic Ash Advisory Centres) and are located across the globe at nine strategic locations. All these nine centres were established in 1991, and are inter-connected as well as in full communication with local meteorological and aviation agencies. The OACI with the help of its VAACs has adopted the following strategy to encounter the problem of Volcanic Ash: • • • •

•

Volcanic Monitoring and Eruption Forecasts o Seismic Monitoring, Visual Observations and Remote Sensing Detection and Tracking of Ash Clouds o With Satellites and Visual Observations Forecasting Ash Cloud Trajectories o Through Stochastic Models and Empirical Relations Education of Pilots, ATC and aviation industry in general o Training of Pilots and Engineers o Details in Flight and Maintenance Manuals o By encouraging research
Through Symposiums
Through Workshops Warning and Avoidance o Quick and Simple warnings to Pilots o Also provided to Airports – ATC o Graphical warnings preferred these days

In this document, we shall be focusing on effects of the volcanic ash on aircraft and specifically engines, and what can be done to prevent any damage. Details regarding other aspects of Volcanic Ash, such as, tracking, predicting and monitoring of Volcanic Ash can be found in reference documents.

8.2.2 EFFECT ON AVIATION As mentioned earlier, in the last three decades over 100 aircrafts have sustained flight encounters with volcanic ash. That number can be considered a minimum value, because not all encounter incidents are publicly reported. These numerous instances of aircraft flying into volcanic ash clouds have demonstrated the serious damage that can be sustained. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Ash particles not only affect the aircraft, but also airports – their landing strips and their operations, making air traffic management more difficult. In order to avoid damage to aircraft and for safety of individuals, flights operations are cancelled in environment affected by Volcanic Ash Clouds, which results in severe economic loss suffered by the aviation industry. Further no solutions exist till date to prevent affect of Volcanic Ash, and the best strategy is to avoid any ash encounters. Aircraft have been damaged by eruptions ranging from small, recurring episodes (e.g., Etna, Italy, 2000) to very large, infrequent events (e.g., Pinatubo, Philippines, 1991). Severity of the encounters has ranged from minor (acrid odor in the cabin and electrostatic discharge on the windshield) to very grave (engine failure requiring in-flight restart of engines). Locations of 32 source volcanoes whose eruptions impacted airports or produced ash clouds encountered by aircraft are shown below:

Figure 15: Locations of Volcanoes that have affected Aviation in the past It can be seen that most of the volcanoes affecting aviation are located in the so-called “Ring of Fire”; but due to rapid and unpredictable movement of ash clouds the encounters have taken place in regions far away from the source volcanoes. Next, we see the effect on ash on aircrafts.

8.2.3 EFFECT ON AIRCRAFTS The various incidents reported above of flight encounters with volcanic ash have shown us that serious damage can be sustained to the aircraft and engines. Ash particles are angular fragments having the hardness of a pocket-knife blade and, upon impact with aircraft travelling at speeds of several hundred knots, cause abrasion damage to forward-facing surfaces, including windscreens, fuselage surfaces, and compressor fan blades. Experimental tests determined the following mechanisms that can affect aircraft performance due to exposure to a volcanic ash cloud: • • • • • •

Abrasive erosion of all leading edge surfaces of fuselage, wing and tail Deposition of material on hot-section components, Erosion of compressor blades and rotor-path components, Blockage of fuel nozzles and cooling passages, Contamination of the oil system and bleed-air supply, Opacity of windscreen and landing lights,

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• • • • •

Contamination of electronics, Compressor stalls, Blocking of Nozzle Guide Vanes, Erosion of antenna surfaces, and Plugging of the pitot-static system which indicates the airspeed of the aircraft.

Figure 16: Effect of Volcanic Ash Encounter on an Aircraft Other problems are encountered at airports while landing and take off which include: • •

Reduced runway friction coefficient, especially when the ash is wet, Loss of local visibility when ash on the ground is disturbed by engine exhausts • Deposition of ash on hangars and parked aircraft, • Structural loading on aircraft very high due to ash (specially wet ash) deposits - Since wet ash has a density of 1000-2000 kg/m3 • Contaminated ground-support systems. Quite often, the volcanic ash cloud is not visible to the naked eye or the instrumentation; if that is the case, the following phenomenon help to indicate an inadvertent entry into a Volcanic Ash Cloud: • • • • •

Smoke or very fine dust in cabin Acrid odor (like electrical smoke) Low air-speed indications Cargo fire warnings (caused by ash triggering smoke detectors) Static discharges (St. Elmo's fire) around windscreen, or on wing, stabilizer, or fin tips • White glow (searchlight effect) at engine inlets • Multiple engine malfunctions (increasing EGT, power loss, stall or flameout). It should be noted, though, there have been ash encounters where none of the above indications were observed after encountering volcanic ash. One such encounter was in 2000 when an experimental NASA DC-8 aircraft flue into dilute ash cloud. The ash cloud was not visible and no abnormalities were detected during flight. Only after ground inspection, it was found that volcanic ash damaged and was deposited in engine ducts. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Subsequently, three engines were to be removed from the aircraft. Clearly, much can be learned from analysis of flight encounters with ash clouds. However, at times, it is very difficult to predict and locate ash clouds and encounters due to visibility and the uncertain wind currents in upper atmosphere. CLASS

PROPERTY

0

Acrid Odour (e.g. sulphur gas in cabin) , Electrostatic Discharge (St. Elmo's Fire) on Windshield, Nose, Engine No notable damage to exterior or interior

1

Light dust in cabin; No oxygen used, EGT fluctuations with eventual return to normal Values

2

Heavy cabin dust; "dark as night" in cabin, External and Internal abrasion damage, Deposit of Ash in Engine, Window Frosting, Severe contamination of air systems requiring the use of Oxygen

3

4 5

Engine Vibration, Erroneous instrument readings, Hydraulic-fluid Contaminations, Damage to Engine, Damage to Electrical Systems Engine failure requiring in-flight restart Engine failure or other damage leading to CRASH Table 24: Ash-Encounter Severity Index

In order to categorize and study, ash encounters they are classified based on the “Severity” of encounters. The encounters are divided into 6 Classes, based on the indications observed during the flight and damage incurred. It should be duly noted that there have been no Class 5 encounters till date. In order to this to continue, detailed procedures to avoid ash clouds once encountered have been specified and are required to be included in Flight Manuals or Service Bulletins. Similarly, detailed maintenance procedures after an encounter with Volcanic Ash Clouds are required to be mentioned through Service Bulletins.

Figure 17: Condition of an Aircraft after Volcanic Ash Accumulation ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Timely warnings need to be issued in order to avoid any ash encounters. These warnings should be of sufficient fidelity so that no damage is caused to aircraft operations and at the same time operations are not stopped unnecessarily. Also these warnings should be easy to understand and hence graphic. We next describe the procedure of issuing these warnings and the details of the “Fly Zones”.

8.2.4 NOTIFICATIONS AND WARNINGS Early notifications and timely warnings regarding Volcanic Eruptions are the primary means through which any accident can be avoided. The warnings must be simple and fast. They should also be easy to comprehend and hence issued with the help of a graphic colour code. Lastly, the warnings should be of sufficient fidelity and should be issued based on careful observations and analysis. Generic and simple alert levels are issued by VAACs for volcanoes under its region, which help provide timely notification of an eruption to the aviation community. These are described as follows:

Colour

Term

Description Normal non-eruptive state; typical background activity

GREEN

Forecast No Eruption anticipated

An eruption in possible in next few weeks and may occur with little or no additional warning Escalated or sustained intense Explosive eruption is possible unrest indicating eruption within a few days and may occur ORANGE WATCH likely, timeframe uncertain, with little or no warning. OR, eruption underway which Ash plume(s) not expected to poses a localized hazard reach 25,000 feet above sea level Major explosive eruption Hazardous eruption is expected within 24 hours. Large RED WARNING imminent ash plume(s) expected to reach at (within hours) or underway least 25,000 feet above sea level

YELLOW ADVISORY

Elevated unrest above known background activity

Table 25: Alert – Levels for Volcanic Eruptions Apart from these alert levels, NOTAM (Notice to Airmen) and specific bulletins are issued by the specific aviation agency in order to notify the aviation community and to ensure smooth and safe air traffic. In order to, issue these notifications and warnings, the Volcanoes need to be continuously monitored. Due to their sheer number, and to add to it, their geographic locations it is practically and economical infeasible to monitor all the volcanoes. Hence, for issuing proper and timely warnings forecasting based on seismic data is done. However, this forecasting is far from perfect due to the unpredictability of volcanic eruptions and rapid movement of volcanic ash clouds. Thus, pilots are required to report of their visual observations of unusual phenomena at volcanoes or presence of ash clouds. A volcano observatory often tries to corroborate a pilot report of eruptive activity against other data, as a volcano can experience increased steaming or display unusual local cloud effects not related to actual eruptive activity. It is only with proper support, multiple data and verification, that correct and timely notifications regarding eruptions and ash cloud be issued. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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8.2.5 FLY ZONES VAACs use volcano-observatory reports, satellite data, and ash-dispersion models as the basis to predict and forecast the ash cloud trajectories. Based on forecasting and observations it is decided whether flight operations should or should not be allowed in a specific region. As we know, an ash cloud eventually dissipates in the atmosphere, and ash concentrations drop. However, the threshold concentration at which ash poses no harm to aircraft is not known, and indeed, may never fully be characterized for all situations involving aircraft. It is usually assumed that ash identifiable on satellite images continues to present a hazard to aircraft. The concentration of volcanic ash in the atmosphere following an eruption is commonly referred to by volcanologists as the “mass loading”. The mass loading in the umbrella region off the column typically varies approximately linearly with the height of the volcanic ash column, from around 2 500 mg/m3 for a column reaching 7 km to over 20 000 mg/m3 for one reaching 40 km. It has been estimated that the volcanic ash concentration encountered by the KLM B747 during the Mt. Redoubt eruption in December 1989 was of the order of 2 000 mg/m3 and caused temporary engine failure. Accordingly, the consensus of the aviation community is that if an ash cloud can be discerned, it should be avoided. However, recently during eruptions of Eyjafjallajokull, due to advancements in technology, it was possible to detect the volcanic ash clouds as low as 0.2 mg/m3. Initially flights were disallowed in ash clouds of densities up to 2 mg/m3, as it was not clear how low is low to prevent damage. Though, soon after due to the prolonged activity of Eyjafjallajokull, problems caused in transportation and severe economic losses suffered by the aviation industry, it was decided to revise the criteria and allow flights based on more analysis. However, proper care was to be taken as any negligence could result in accident, and studies indicated that even low concentration ash could produce long term damage to the aircraft and specifically its engines. Thus after careful and detailed analysis, regions based on prediction of cloud trajectory and mass loading were divided into “Fly Zones”. These fly zones are primarily characterized by the mass loading of Volcanic Ash, and specified timely maintenance and inspection of aircraft and engines to avoid any damage. These zones were specified as follows: •

•

No Fly Zone o Zone 1 o Mass Loading : Greater than 4 mg/m3 o Area of high density Volcanic Ash o Includes the main area/core of the volcanic fall-out, with an additional buffer zone o Established based on basis of meteorological conditions where wind direction, humidity, etc, will result in high intensity of ash particles o Depicted by Colour – BLACK Time Limited Zones o Zone 2 o Mass Loading : Between 2 and 4 mg/m3 o Potential Contamination Zone o Area of low density Volcanic Ash Contamination

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An area outside Zone where flying can be conducted when actual conditions, risk assessment and test(s) can establish, that flights can be conducted at an acceptable level of safety o Requires authorization and prior permission from the operators o Flight operations allowed for only limited period of time o Detailed inspections and maintenance necessary both before and after the flight o Depicted by colour – GREY Enhanced Procedure Zones o Zone 3 o Mass Loading : Between 0.2 and 2 mg/m3 o An area free of contamination where flights can be conducted without any restrictions or special prerequisites o Depicted by colour - RED o

•

The figure on the next page illustrates the various fly zones allotted for the eruptions of Eyjafjalljokull. These zones are updated every six hours and this should be taken into account by the operators. Further, these zones are 3 dimensional in nature and different contour maps exist for different height levels.

Figure 18: Fly Zones – An Illustration Most of the engine failures till date have taken place at a mass loading of 2000 mg/m3 or more. Though, this cannot ensure that flight in Time Limited Zones will be without any after effects, but with proper maintenance both before and after the flight the extent of damage caused by flight in Time Limited Zones can be greatly minimized. Now, we discuss effect of volcanic ash on engines and suggest maintenance procedures for the same. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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9 VOLCANIC ASH AND ENGINES Potential engine damage caused by the ingestion of dust or ash-laden air is a serious consideration for the operation of gas turbine engines on unimproved runways or in dusty environments. Several different mechanisms can be active in altering engine performance during or after exposure to a dust-laden environment. In this section, we discuss effect of Ash Ingestion on Aviation Engines. The following chapter is focussed specifically on effect of volcanic ash on engines. Firstly, the effect of Volcanic Ash on engines is described and a numeric analysis is presented to understand the severity of the problem. A comparison of Volcanic Ash has been made with other contaminants which affect engine performance. Next, the current solutions and various service bulletins regarding engine maintenance with regards to Volcanic Ash have been compiled. Finally, some solutions and suggestions in regards to engine cleaning and maintenance after an encounter with volcanic ash have been presented. These suggestions have been derived from open literature and by comparison of volcanic ash with other critical phenomenon related to engine cleaning.

9.1

M AJOR EFFECTS For most modern engines (including Arrius, Arriel and Makila) during design (for better performance) the operating line is trimmed as close to the surge line as is possible. This operating line has a built in margin for known/predictable degradation terms such as inlet distortion, transient gusts, and normal component wear. Encountering a particle laden environment of the type of interest here falls into the category of an unanticipated degradation and may be manifested in one or more of the following ways: • Glassification of hot-section components • Erosion in compressor blades and rotor paths • Blockage of cooling paths • Oil system or bleed air supply contamination

Figure 19: Deposits of Re-melted Volcanic Ash on NGV The response of a jet engine when exposed to volcanic ash depends on a number of variables, including the concentration of the ash, engine type, engine thrust setting, time of exposure and ash composition and has been investigated for the past two decades, through the strip-down inspection of jet engines which have been exposed to volcanic ash clouds and through ground tests. Though, a lot of effects are observed, there are mainly four ways through which Volcanic Ash affects jet engines: ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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•

Melting point of Volcanic Ash o Volcanic ash has a melting point of around 1000°C , which is below the engine core temperature of around 1400°C o The ash melts in the hot section of the engine and fuses on the high pressure Nozzle Guide Vanes and Turbine Blades o The turbine inlet throat area reduces and increases compressor exit pressure o Compressor Surge is eventually caused o Surge causes immediate thrust loss and possible engine flame-out

•

Hardness and Abrasive o The volcanic ash is very hard and also abrasive o Sand blasting effect due to the speed of ingestion o Erodes compressor rotor paths and rotor blade tips o Causes loss of engine efficiency and thrust o Corrosion also could result in loss of stall margin o This effect is permanent and irreversible and usually requires engine overhaul o Reduction of engine thrust to idle reduces the rate of erosion

•

Clogging o Clogging of flow holes in the fuel and cooling systems o Makes engine restart very difficult o Increases Exhaust Gas Temperature and temperature inside the engine o Causes reduction in T4.5 Margin and other long term effects

•

Chemical gases o Volcanic Clouds apart from ash also contain gases including water vapour, sulphur dioxide, chlorine, hydrogen sulphide and oxides of nitrogen o No immediate effect after ingestion o After some time, oxidation and hydration of SO2 forms H2SO4 o The resulting ash/acid mixture is highly corrosive o Corrosive long term damage to engines o Also deposits in Turbine Section after solidification

Figure 20: Compressor Tip Erosion due to Volcanic Ash

9.2

ASH INGESTION – AN ESTIMATE Amount of Volcanic Ash ingested in an engine governs the damage caused and maintenance required to an engine; and is itself governed by the operating characteristic of the engine and mass loading of the aircraft.

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Hence, to understand the gravity of the situation we carry out a ball-park estimate of the amount of ash ingested into the engine during a flight. The flight operation considered is an average flight operation with following parameters:

Property Time of flight Concentration of ash (Mass Loading) Rate of Air Intake Altitude Density of air Air Volume Flow Rate Ash Mass Flow Rate Ash Mass Flow

Value

Unit 60 min 4 mg/m3

6.36 kg/s 10000 ft 0.9 kg/m3 7.07 m3/s 28.28 mg/s 101.81 g

Table 26: Parameters for Ash Ingestion Analysis • •

• • • •

• •

The time of flight o One hour Concentration of ash o Same as that encountered in Time Limited Zones (Fly zones where Volcanic Ash exists but flight is allowed for a limited period of time) o This should be contrasted with the fact that the most polluted cities have dust concentration lower than 0.004 mg/m3 o The value of Mass Loading shall always be higher for No Fly Zone, if rotorcraft goes near the volcano it can encounter ash concentrations up to 40000 mg/m3 Rate of Air Intake, G o 6.36 kg/s o Has been taken same as that for Makila 2A (Arrius and Arriel have lower value of G) Altitude of Flight o 10000 ft (~3000 m) Density of Air o 0.9 kg/m3 at given altitude based on ISA Air Volume Flow Rate o Indicates volume of air ingested into air per second o 2.78 m3/s o = ( Rate of Air Intake )/ ( Density of Air ) Ash Mass Flow Rate o 3.06 mg/s o = (Mass Loading)*(Air Volume flow rate) Ash Ingestion in a hour long flight o 101,81 g o = (Ash mass flow rate)*(Time of flight) o The same analysis for 5000 ft yields ash ingestion of 86 g

Amount of Volcanic Ash ingested in an engine governs the damage caused and maintenance required to an engine; and is itself governed by the operating characteristic of the engine, the altitude of flight and the mass loading. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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The order of magnitude analysis tells us that a lot of ash gets ingested into an engine (~100 grams), even when we flying in an environment with a relatively low mass loading of 4 mg/m3. If the aircraft or helicopter is in a denser volcanic cloud (e.g. KLM B747 was in a cloud with mass loading of 2000 mg/m3) the amount of ash ingested would be very high and would weigh in kilograms. Clearly, this will deteriorate the engine heavily and may even cause its life to end. Hence, it is always advised to avoid flight in ash-laden environment. The amount of ash ingested in Time Limited Zone is limited if the engine is flown for a limited period of time and hence flight after comprehensive inspections and maintenance (as required by airworthiness) are allowed to fly for a limited period of time even in ash clouds (though of low mass loading). The amount of ash ingested is contrasted with dust levels in heavily polluted cities, and the lowest density of ash in No Fly Zones is around 1000 times more than the heaviest polluted cities. Thus, prevention by filtering of volcanic ash just because of its amount is very difficult. Apart from this, it should be noted that in this analysis the concentration of ash, we have taken into account the effect of only abrasive damage; due to sulphur vapours in volcanic ash cloud more damage or erosion might occur to the engine and specifically compressor-turbine blades. In order to allow flights in Time Limited Zones and Enhanced Protected Zones, and also for the safety and longevity of the engine life, specific maintenance procedures need to be specified. Engine Cleaning plays an important in recovering performance and preventing corrosion of turboshaft engines when affected with contaminants such as sand, dirt and chemically corrosive environment. The effects and problems of these contaminants on engines are compared next with that caused by volcanic ash, in order to specify maintenance procedures for turboshaft engines, specifically for the operation of Engine Rinsing, Washing and Cleaning. Till now we have seen the basics of how volcanic ash affects engines, now we shall propose some solutions and suggestions for combating the same based on a comparative analysis with other contaminants and by analysing existing procedures.

9.3

OTHER CONTAMINANTS Volcanic Ash is a contaminant which enters the engine through the air path and causes it to malfunction. Other contaminants also exist with somewhat similar properties which enter the engine through the air path causing problem. These phenomenon include sand and corrosive chemical air. The problem of volcanic ash is somewhat infrequent and rather recent, while contamination due to sand and corrosive chemicals is far more common and is regularly encountered in deserts and off-shore regions, respectively. Due to this reason, detailed studies have been carried out regarding interaction of sand and corrosive air with the engine. Solutions and detailed procedures for engine cleaning exist for the above-mentioned cases and can be useful in determining procedures related to Volcanic Ash. In this section, we discuss basic effects of sand and corrosive air on the helicopter engine and compare them with that due to Volcanic Ash.

9.3.1 SAND Gas turbine engines often encounter conditions of dirt or sand ingestion into the air duct. Such ingestion may occur during landing or take-off in desserts, due to unpaved helipads, during brown out, etc. As, most of the aviation engines do not have inlet filtration, particles enter in both the main air stream as well as the by-pass stream meant for cooling. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Figure 21: Sand Ingestion during Take-off Sand ingestion can thus result in the following problems: •

• • • •

Cooling of the Engine o Blocking of the coolant passages o Blocking of film-cooling holes o Adheres to the surface of engines o Reduces the heat transfer from coolant to metal surface o Increased airfoil and engine temperatures o Reduces Convention and Increased thermal resistance Decreases Mass Flow Rate by clogging Reduction in service life (Abrasive effects – Sand Blasting) Mechanical Corrosion – Results in loss in efficiency Melting of particles beyond 1000 °C

9.3.2 CHEMICAL ENVIRONMENT Engines operating in off-shore condition (especially in oil and gas industry) frequently encounter chemically corrosive conditions. Helicopters are a prime requirement for offshore oil and gas industry, and detailed Cleaning procedures thus exist for helicopter engines encountering chemically corrosive atmosphere. Marine or saline environment for engines is usually termed as any flight operation in proximity to the sea or above salt water at an altitude of less than 250 ft and in a perimeter of 5km/3 miles inland. The main problems caused are: • •

Chemical Corrosion o Reacts with water and becomes corrosive o Corrosion of engine parts Formation of deposits o Result in decrease of engine performance

9.3.3 COMPARISON WITH VOLCANIC ASH Till now, we have seen the damages caused by Volcanic Ash, Sand and Chemical Environment. Broadly, it can be observed that the damages caused by Volcanic Ash are a combination of the damages caused due to Sand and that caused due to chemically corrosive environment. ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Both Sand and Volcanic Ash are abrasive and have similar physical effects. This is also due to the fact that the primary component of both the contaminants is silica which produces the abrasive sand-blasting effect. Volcanic ash, since it contains a lot of chemicals in forms of gases, it also exhibits the same chemically corrosive action exhibited in Marine or Salty Environment. Apart, from the above properties of sand and chemical environment, Ash additionally has the problems of •

Particle size o Ash can have particles of very small size o Filtering is very difficult • Un-predictability o Volcanic Ash is rare and infrequent o Thus, being preparation and detection at all times is difficult o At times a Volcanic Ash encounter may go un-noticed • Re-deposition at the Nozzle Guide Vane • Other contaminants, specifically sand, usually enter into engine only while landing or take-off, on the other hand, ash clouds interact with engines at fully operating conditions and in-flight making them more dangerous and difficult to deal with Thus, we can see, in order to maintain engines after encounter with volcanic ash it is necessary to perform the maintenance procedures related to engines affected with sand as well as that with chemical environment. This is the minimum amount of maintenance which needs to be done, as Volcanic Ash can have some additional effects. Also, while specifying maintenance procedure for volcanic ash, further care needs to be taken whether no side effects appear on application of existing procedures on to the engines.

9.4

ENGINE MAINTENANCE It is best to avoid flights in Volcanic Ash, since many a times engine can experience expensive and long term damage. However, for regions of low concentration of volcanic ash, where flights are allowed, maintenance procedures have to be defined for safety and proper operation of the engine. Since, effect of ash is stochastic in nature even low concentration could cause large damage, If excessive damage is done to the engine, nothing much can be done, and overhaul is mandatory; but usually if flight is undertaken in Time Limited Zones or Enhanced Procedures Zone, by timely maintenance engine performance may be recovered. In this section, we first go through the existing procedures for treatment after Volcanic Ash; and then suggest some solutions in order to improve them.

9.4.1 CURRENT PROCEDURES The problem of Volcanic Ash is rare and rather recent; and flights in ash-laden atmosphere are a strict no-no. Thus, detailed maintenance procedures for engines encountering with Volcanic Ash do not exist. Historically, flight operations were strictly not allowed in ash atmospheres. Though, due to the prolonged activity of Eyjafjallajokull and the economic effects it had, it was decided to divide regions into various Fly Zones (see Section 8.2.5) and selectively allow flight based on mass loading of ash clouds. For airworthiness of flights in Time Limited Zones (with Mass Loading: Between 2 and 4 mg/m3), it was made necessary for operators to have ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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detailed maintenance procedures for both before and after the flight in Time Limited Zones and inadvertent flights in No Fly Zone. Since, the problems caused by Volcanic Ash are similar in nature to that caused by sand ingestion and chemically corrosive environment; maintenance solutions on the lines of following were recommended: • Treatment after operations in salt, corrosive or polluted atmosphere; as well as • Treatment after operations in sandy atmosphere (deserts or brown outs) However, as we saw earlier (see Section 8.4) the properties of Volcanic Ash and the other contaminants though similar are not same; hence, blind application of these procedures might not eradicate the total problem and also cause some side effects. Now, we discuss the solutions proposed by various Engine Manufacturers post 2010Icelandic eruptions of Eyjafjallajokull.

9.4.2 SERVICE BULLETINS Service Bulletins or Service Letters specify changes or addition to the maintenance procedures, due to evolution of procedures or new problems. Due to the Iceland eruptions, it was mandatory for all engine manufacturers to release Service Letter/Bulletins specifying maintenance procedures for operations in volcanic ash clouds. We compare the service bulletins released by different Engine Manufacturers • Turbomeca o In Flight Procedure -Monitoring of flight parameters and operating conditions
Outside temperature
Relative wind
Presence of particles, fumes or turbulences o Maintenance programme
for salt, corrosive or polluted atmosphere
for sandy atmosphere o If ash deposits detected, contact Field Representative before further use of engine

Engine Wash/Clean Procedure Periodicity Boerscope Inspection PAC

Pratt n Whitney Not Written

Rolls Royce Yes

Turbomeca Yes

Honeywell No

-

With Water After Flight

With Water After Flight

Vacuum Cleaning After Flight

Yes Yes

Yes Yes

Yes -

Yes Yes

Acceleration Check

Yes

Yes

-

Yes

Filter – Inspection Periodicity – TLZ

Yes

Yes

Yes

Yes

10 hrs

After Flight

-

After Flight

Periodicity – EPZ

50 hrs

25 hrs

-

25 hrs

Table 26: Comparison of Volcanic Ash Service Bulletins •

Honeywell o The maintenance programme suggested is based on different “Fly Zones”, which is logical since different amounts of ash ingestion takes place in different zones

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Procedures for No Fly Zone and Time Limited Zones
Post Flight Inspection for signs of ash contamination of: • Inlet area including axial compressor • Temperature Sensors • External Parts of the engines • Air Filters
Cleaning • Of exterior of the engine and complete airframe of inlet • Using only shop air, vacuum and wiping with approved solvent (no use of water) • Recommendations not to use pressure wash equipment or fluid spray cleaning due to the possibility of relocation of large deposits and hardening of ash
On condition monitoring for detection of ash • Borescope inspection of accessible nozzles and blades
If ash detected even after cleaning contact Engine manufacturer before returning the engine to service
If no contamination after cleaning do procedures listed for Enhanced Procedures Zone o Procedures for Enhanced Procedures Zone
Do all checks for No Fly Zones • If no contamination, proceed to following steps
Inspect and clean the air system
Clean and inspect all pneumatic type equipments
Change the engine fuel and oil filters • after every 25 hours until operating in EPZ
Check and if required change the air filter every 25 hrs
Acceleration Check - there should be no surge observed
PAC- trend monitoring at every 25 hrs
Compressor Cleaning with water and pressurized equipment after 50 hrs operation in ash free zone Rolls Royce o Acceleration Check – No Surge should be observed o Compressor Wash with water and pressurized equipment
Every 25 hrs - if Enhanced Procedures Zone
End of every flight - if No Flight Zone or Time Limited Zone
Wash the compressor and components using an approved solution o Flush the engine oil system. o Clean or replace the engine oil filter, fuel filter and air filter. o For aircraft equipped with bleed valves: - clean the bleed valve air system o Perform compressor erosion inspection. o Trend monitoring of engine to predict and avoid any future problems o

•

•

Pratt and Whitney, PWC o Provided procedures only for Time Limited Zone o Visual and Borescope inspection for sign of ash and erosion
Specifically erosion of compressors
Fuel Nozzles o No specific mention of Engine Washing or Cleaning o Monitoring of Oil Filters and Fuel Filters

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o o o o

Monitoring of Bleed Valve, Air Path and Air System Acceleration Check Performance Assurance Check Periodicity –
During the operations in TLZ – every 10 hours
After volcanic ash conditions have ended – every 50 hours

A lot of similarities could be found in the maintenance procedures specified by different engine manufacturer, though contradictory suggestions do exist. Specifically, there is no consensus whether washing of engines should be done after an ash encounter and whether water must be used or not. Based, on properties of Volcanic Ash and research studies available some procedures are suggested which could be followed in event of Volcanic Ash encounter.

9.4.3 SUGGESTIONS – ENGINE CLEANING As seen in the previous section, there is some disagreement on the use of water in cleaning of engines post-flight in Volcanic Ash. Treatment after exposure with either sand or chemically corrosive environment requires thorough cleaning of engines with the help of pressurized equipment and water. However, in the case of Volcanic Ash, there is slight difference, in the fact that water at times can turn the ash to sludge or causes it to harden. However, some studies also find cleaning to be ineffective if the ash is not slightly wet. In order to find a fool-proof solution, detailed computational and experimental studies can be carried out, but some quick engineering solutions can be derived from the literature, which are bound to work in most of the cases. The following pointers can be used while specifying a modified cleaning procedure • Vacuum Cleaning (Dry wash) of the engine o Clean the engine first with only shop air and shop vacuum (similar to vacuum cleaning) o Do not scrub or wipe engine before Vacuum Cleaning (dry wash) o Do not use any water o To be performed using dry crank (ventilation) o This shall drive out most of the dry ash o However, wet ash if already present will still remain inside the engine duct • Engine “Washing” with Hot Water o Use warm to hot water (from 50 to 70°C) for washin g o To be performed using dry crank (ventilation) o Use specified chemicals, as mentioned in Maintenance Manual
Specific Chemicals for Volcanic Ash can be recommended by the Engine Manufacturer o Wash first without soaking and at low concentration (~2%) of cleaning products o After the Wash is performed, inspect engine for any signs of ash hardening
If the wet ash is hardening, • Clean the engine with only shop air and vacuum • Contact Field Representative ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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If the wet ash is getting removed - modified Engine Cleaning Modified Engine “Cleaning” with Hot Water o Use warm to hot water (from 50 to 70°C) for cleani ng o To be performed using dry crank (ventilation) o Use specified chemicals, as mentioned in Maintenance Manual
Specific Chemicals for Volcanic Ash can be recommended by the Engine Manufacturer o Let the cleaning mixture soak for specified time and use high concentration (~20%) of cleaning products o Clean the engine with only shop air and vacuum o Perform drying of the engine After above procedure, do borescope inspection o If the ash still persists and is not fully removed
Contact Field Representative o If the wet ash is getting removed
Procedure is finished
Proceed to protection and covering of engine Protection and Covering of Engine o Once on ground engine should be properly covered by installing blanks o Internal and external protection of engine should be performed

The method suggested above is far from fool-proof and only after proper verification and validation should they be used on engines. These are only generic suggestions applicable to a gas turbine engine in general. However, before adopting them for a specific engine tests should be carried out by the engine manufacturer in order to check for any undesired effects. Apart from validation, engine specific cleaning products and different frequencies of maintenance procedures can also be specified by the engine manufacturer.

9.4.4 SUGGESTIONS – SERVICE BULLETINS In the previous section we specifically considered the case of engine cleaning after encounter with Volcanic Ash. Other maintenance procedures also need to be carried out for ensuring proper functioning of the engine. Following maintenance procedures should be performed post encounter with Volcanic Ash: •

Post-flight procedures o Borescope inspection of accessible
gas generator nozzle,
gas generator turbine blades, and
power turbine blades,
air duct o Corrosion Check of
Compressor blades
Turbine Blades o Check for clogging of
Fuel nozzles and indicators
Cooling holes o Perform Modified Engine Cleaning
as specified for procedures after encounter with ash cloud

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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Inspection and if necessary cleaning and replacement of some selected (which could be affected by ash ingestion – based on engine architecture)
Oil Filters
Fuel Filters
Pneumatic Devices and Air Filters
Bleed Valve Perform Acceleration Check
Surge should not be encountered Proper protection of the engine
Engine should be kept properly covered in Volcanic Ash affected helipads and airports

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Periodic procedures o Trend Monitoring of the engine
To recover performance
To predict and avoid further problems o Inspection and if necessary cleaning and replacement of
Oil Filters
Fuel Filters
Pneumatic Devices
Air Filters
Bleed Valve
Periodicity • Every 25 hrs when operated in EPZ • After every flight when operated in TLZ and NFZ

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In-flight procedures o Monitoring of flight parameters
Outside temperature
Relative wind o Operational conditions to be monitored
Presence of particles, fumes or turbulences
To make sure helicopter operates within flight envelope and current regulations

The above procedures will help in maintaining the safety of the engine in areas of low mass loading of Volcanic Ash. However, operation of gas turbine engines in a volcanic ash-laden environment is not advised and should be avoided due to numerous potential operational and maintenance issues. The long term effects of exposure to volcanic ash are not certain. The long term effects may manifest themselves hundreds of hours later. Apart from the above procedures, any and every encounter with Volcanic Ash should be • Recorded in log book, • Based on recommendations from OACI and concerned agencies, the crew and maintenance team should be equipped with proper knowledge regarding Volcanic Ash • In case of non-removal of ingested ash, even after performing prescribed procedures o Field Representative should be contacted o Engine should be grounded and properly stored ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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9.5

LONG TERM SOLUTIONS To quote the manual on Volcanic Ash “At present, the recommended procedure in the case of Volcanic Ash is – regardless of ash concentration is – AVOID AVOID AVOID”. The sentence is befitting since, no precise values of ash concentration can be defined which do or do not constitute a hazard to engines. However, this should not stop us from looking solutions which could completely eradicate the problems of Volcanic Ash. Surely, solutions will not be easy and may even not be economically feasible; but without proper analysis they should not be discarded. In this section we list some open-ended approaches (at the very basic level) towards minimizing and/or eradicating the problem of Volcanic Ash for Engines. These ideas, as mentioned are open-ended, and may or may not be economically feasible; although, for sure they warrant further study and might turn out to be “the” solution.

9.5.1 FILTERS The simplest way to “Avoid” damage to engines is by “Avoiding” ash ingestion into them. This can be done in two ways • Avoiding engines to enter ash-laden atmosphere – Current Approach • Avoiding ash to enter engines – Filters However, the design of filter is very difficult, due to • The high variance in size of ash particles (0.0001 – 1 cm) • The amount of ash ingested (~100 g/hr in moderately concentrated No Fly Zones)

9.5.2 ELECTROMAGNETIC PROPERTIES Volcanic Ash exhibits some electric properties, such as, St. Elmo’s fire (similar to Electrostatic Discharge). This indicates present of ions in the Volcanic Ash. Ash also has various minerals, which could have magnetic properties. By exploiting the electromagnetic properties of Volcanic Ash, ash ingestion if not prevented could be minimized.

9.5.3 DEVELOPMENT OF SOLUTIONS In order to develop the long term solutions, it is necessary that proper and channelized development is done. Listed below are few pointers regarding the same: • • •

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Economical Survey o An order of magnitude estimate-study for development of solutions o In order to decide, whether further work shall be economically favourable Theoretical Studies o Through analytical or mathematical models o Computational simulations Experimental Studies o Through test benches and facilities o Ground test of engines by controlled injection of volcanic ash into the engines Exploring further ideas o Brainstorming and exploring newer ideas o It usually takes a combination of various ideas to lead to a solution

ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.

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9.5.4 ENGINE DESIGN Due to the seriousness of the problem it is necessary that based on experience, some consideration is given to the problem of Volcanic Ash directly during the “design” of upcoming engines. This requires, during engine design, the development of: •

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Smart Relight Systems o Engine restart during flight should be facilitated by smart relight systems included in the control systems while design o Addition of a time-delay circuit to allow an air-started engine to reach stabilized idle speed before the electrical or generator load is applied. This would facilitate engine restarts under less-than-ideal conditions In-flight Procedures o Detailed in-flight procedures specifying maximum engine power levels (expressed in engine pressure ratio (EPR), fan speed (N1), and (or) exhaust-gas temperature (EGT) levels) that will minimize build up of melted and re-solidified ash on nozzle guide vanes.

9.5.5 SUMMATION Current techniques for reducing the impacts of volcanic ash are basically “low tech” and depend more on procedural approaches than on technical fixes. Also, they are quite labour and resource intensive. However, it should be kept in mind that, engines faced similar (though less challenging) conditions with sand ingestion (and brown out) a few years ago, which now have been combated. Thus, with proper analysis and development of above mentioned ideas, better technical solutions could be made available, to protect the Engines from Volcanic Ash.

10 REFERENCES 1. 2. 3. 4.

Turbomeca Maintenance Manuals - Arriel 2S 2, Makila 2A and Arrius 2B 2 Turbomeca Training Manuals - Arriel 2S 2, Makila 2A and Arrius 2B 2 CCT 800 - Standard Conditions for Rinsing, Washing and Cleaning Turbomeca Engines F.C. Mund and P. Pilidis – Gas Turbine Compressor Washing: Historical Developments, Trends and Main Design Parameters for Online Systems 5. J. Stadler – Gas Turbine Compressor Washing State of the Art: Field Experiences 6. F.C. Mund and P. Pilidis – Compressor Washing: A Numerical Survey of Influential Parameters 7. M. P. Boyce and F. Gonzalez – A study of Online and Offline Turbine Washing to Optimize the operations of a Gas Turbine 8. R. Kurz and K. Brun – Degradation in Gas Turbine Systems 9. OACI Doc 9691 – Manual on Volcanic Ash, Radioactive Material and Toxic Chemical Clouds 10. T.J. Casadevall et al. – Volcanic Ash and Aviation Safety: Proceedings of the First International Symposium on Volcanic Ash and Aviation Safety 11. M. Guffanti and Capt. E K Miller – Reducing the threat to Aviation from Airborne Volcanic Ash 12. Volcanic Ash Service Bulletins 13. Resources on internet o volcanoes.usgs.gov o www.volcano.si.edu ENR0090-D Ce document est la propriété de la société Tu rbomeca. Il ne peut être communiqué ou reproduit sans son autorisation© Le texte origina l de ce cahier des charges, écrit en français, fera fo i en cas d’interprétation et/ou de litige entre les parties. This document is the property of Turbom eca and m ay not be copied, used or communicated without Turbomeca’s authoriza tion© In case of misinterpretation and/or dispute, the orig inal text of th is specification, written in French, will be authoritative as between the parties.