Aicraft Reciprocant Engines Week 5 and 6

Aicraft Reciprocant Engines Weeks 5 -6

Eng. JAIRO ANDRÉS GUTIÉRREZ S

Cylinders Place were combustion takes place • Strong to withstand pressure forces • Lightweight metal construction • Good heat conduction properties • Easy – inexpensive to manufacture / inspect / maintain

2

Cylinders • Cylinder consists of cylinder head and the cylinder barrel • Cylinder Head constructed from aluminum alloy • Barrel usualy built from steel 3

Cylinder Head • Provides a place for the combustion to happen • Provides heat conductivity for cooling • Provides a mounting point for valves, spark plugs and their assemblies. • In air cooled engines, cylinder heads must have cooling fins 4

Cylinder Barrel • Usually built from a high strenght material • Steel alloy forging with inner surface hardening • Hardening by exposing steel to ammonia / cyanide gas (cianuro / ammoniaco) -> nitriding • If barrels have got wear they can be overhauled to proper dimensions 5

Cylinder - Numbering

Source: FAA AMT Powerplant Vol 1

Valves

Source: FAA AMT Powerplant Vol 1

Valves • • • •

Intake / Exhaust Valves Mushroom and Tulip Types (Hongo / Tulipán) Subjected to high temperatures, stresses , etc. Intake valves operate at lower temperatures (usually built from nickel chromiun steel) • Exhaust valves operate at higher temperatures: Cobalt chromiun steel or other temperature resistant alloys 8

Aviation Reciprocant Engine Valves

Source: FAA AMT Powerplant Vol 1

Mechanical Arrangement

Inlet Valve

The Inlet Valve needs to be open, to allow the fuel/air mixture in

Exhaust Valve The Exhaust Valve needs to be open, to allow the burnt gases out

Valve Operating Mechanism (Opposed Engines)

Source: FAA AMT Powerplant Vol 1

Mecanismo del eje de levas en motores opuestos – sistema hidráulico

Source: FAA AMT Powerplant Vol 1

Mechanical Arrangement Valve Operation Push Rod Mechanism Rocker

Valve opening motion: 1) Starts at rotating camshaft 2) Camshaft moves a pushrod and lift the rocking lever 3) Through a rocker shaft the valve opens 4) Spring helps the valve returning to its place

Rocker Shaft Return Spring Valve Seat

Inlet Valve Closed Push Rod

Valve Lift Cam Shaft

Mechanical Arrangement Valve Operation Rocker Arm

Cam Shaft

Return Spring

Valve

Overhead Cam and Rocker

Overhead Cam No Rocker

The less parts there are, the more accurate the work with opening and closing times, and the more efficient the engine. Some engines feature a hydraulic system for valve opening (closing via a return spring), but driven by a cam. Some manufacturers now fit VARIABLE valve timing; to ensure that the valves operate at the optimum point at all rpm values to gain maximum efficiency from a piston engine.

Mechanical Arrangement Valve Operation The Cam Drive

Modern Engines use a toothed rubber belt to drive the cam shafts

Twin Cam System

Chain Tensioners Pistons and Crank Shaft Cam Drive Mechanism

Valve Operating Mechanism (Opposed Engines)

Source: FAA AMT Powerplant Vol 1

Mecanismo del eje de levas en motores opuestos

Source: FAA AMT Powerplant Vol 1

Mecanismo del eje de levas en motores opuestos – sistema hidráulico

Source: FAA AMT Powerplant Vol 1

Rodamientos

Source: FAA AMT Powerplant Vol 1

Reduction Gears

Source: FAA AMT Powerplant Vol 1

Source: FAA AMT Powerplant Vol 1

Aircraft Reciprocant Engine Definitions • DISPLACEMENT (CILINDRAJE) • CYLINDER BORE • PISTON STROKE • TOP DEAD CENTER / BOTTOM DEAD CENTER (TPC Y BDC) • COMPRESSION RATIO (RELACIÓN DE COMPRESIÓN • VOLUMETRIC EFFICIENCY| • BRAKE HORSEPOWER

DISPLACEMENT DISPLACEMENENT (CILINDRAJE O DESPLAZAMIENT) REFERS TO THE TOTAL VOLUME DISPLACED BY THE ENGINE IN A THERMODINAMIC CYCLE. IT MAY ALSO REFER TO THE DISPLACEMENT OF A SINGLE CYLINDER DISPLACEMENT= CYLINDER DISPLACEMENT (Cd) * # of Cylinders

ENGINE BORE AND STROKE REQUIRED TO MEASURE ENGINE SIZE “Engine size is determined by the cylinder diameter (BORE), the amount of piston travel (STROKE) and the number of cylinders”

ENGINE BORE AND STROKE

ENGINE BORE Diameter of the engine cylinder Measured across the cylinder, parallel

with the top of the block Cylinder bores vary in size, but typically

range from 3–4" (75–100 mm)

PISTON STROKE Distance the piston moves from top dead

center (TDC) to bottom dead center (BDC) Crankshaft journal offset (throw) controls

the piston stroke

MAIN CALCULATIONS This is the main formula to be used with the given numbers

But also: Crankshaft Offset*2 = stroke

Bore/Stroke Ratio

Bore – to –Stroke Ratio

COMPRESSION RATIO Compares the cylinder volume with the piston at TDC to the cylinder volume with the piston at BDC Ratio of swept volume V1 divided by combustion chamber volume V2 

Clearance volume = combustion chamber volume

Compression Ratio

Source: FAA AMT Powerplant Vol 1

Compression Ratio

Compression Ratio – Gasoline Engine

Compression Ratio – Diesel Engine

Volumetric Efficiency Ratio of air drawn into the cylinder and the

maximum amount of air that could enter the cylinder

• Simply put, it is the ability of the engine to breath in on the Intake Stroke Formula:

Volumetric Efficiency = actual volume of air taken into each cylinder volume of the cylinder

Volumetric Efficiency Engines are capable of only 80–90% volumetric efficiency. Restrictions in the ports and around the valves limit airflow.

Can you name some of the factors that would impede air flow into and engine?

Brake Horsepower Example

Exercises Examples If one piston displaces 25 cu. in. and the engine has four cylinders, what is the engine displacement? 25 cu. in.  4 = 100 cu. in.

If one piston displaces 500 cc and the engine has six cylinders, what is the engine displacement? 500 cc  6 = 3000 cc = 3.0 L

Exercises A continental IO engine has got 6 cylinder, a bore of 5.25in, a stroke 4in. Determine a) Cylinder Displacement b) Engine Displacement & Bore – Stroke ratio

c) Compression ratio if volume in combustion chamber(clearance volume) is 11.5in3

Workshop Draw and calculate an engine with the following parameters: 1)

Cylinder displacement must be between 50 to 100 in3 per cylinder

2)

Compression ratio must be at least 7:1 or more. Maximum compression ratio is 10:1

3)

Cylinder number must be 4 or 6

4)

Calculate crankshaft distance to crankpin

5)

Bore to Stroke ratio from 1:1 to 3:1

Workshop Calculate: 1)

Bore size, Stroke Size

2)

Crearance volume, connecting rod size, crankpin to crankshaft center distance

3)

Draw at scale

4)

Find real displacement with a volumetric efficiency of 90%.

5)

Find the piston average speed if RPM´s are 2700

6)

Use the following website to understand connecting size to stroke (also 2 times crankpin to cranshaft distance) http://www.torqsoft.net/piston-position.html . Compare both your drawing with the website calculations

Assignment 1 – Exposition (35%) • • • • • •

Explain a specific aircraft piston engine system The following options are available: Aircraft engine Fuel System Aircraft engine Induction/Exhaust System Engine Starting, Ignition & Electrical Aircraft engine Lubrication System Aircraft engine Cooling System (liquid and air cooling) Aircraft engine Propeller System (fixed and variable pitch)

Assignment 1 – Exposition (35%) What I want? Groups 3 People – INDIVIDUAL GRADES At least 50 min long presentation • Why is the system important? Main functions • Description and function of system components • A complete exposition of the system (types, parts, system diagram, work scheme, videos, etc) • Use images from bibliography, AMM, IPC, etc • System Diagrams • Indicating Instruments in Aircraft Cockpit (can use Flight Simulator) • Maintenance Practices (basic)

Assignment 1 – Exposition (35%) Nota: La nota se asignará de acuerdo a: • Claridad en la exposición. • Profundidad en la explicación del sistema. • Ayudas audiovisuales • Profesionalismo (ejemplos: bajará nota textos largos leidos, letra pequeña, colores que dificulten lectura, etc.) • Resolución de preguntas

Assignment 1 – Exposition (35%) REFERENCES: • FAA-H-8083-32-AMT-Powerplant-Vol-1 y Vol-2 (gratis) • FAA Pilot Handbook- Chapter 06 (gratis)

(http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot _handbook/media/PHAK%20-%20Chapter%2006.pdf)

• Antonio Esteban Oñate, Conocimientos del Avión (biblioteca) • Aircraft powerplants, Michael J. Kroes Thomas W Wild (biblioteca) • AMM´s, IPC, etc (already given to students)

Assignment 2 (15%) Search for FAA accident records on Reciprocating engines. Find technical documentation on the type (manuals, views, drawings, TC), and explain to class what happened. http://www.ntsb.gov/aviationquery/

Assignment 2 (15%) 1) Explain what happened, and the possible causes, type of aircraft, etc. 2) Use technical documentation to detaily explain the parts involved. Give P/N, location, system components 3) If it involves a system, explain how it works 4) Give conclusions and maintenance recommendations so it wont happen again

Horizontally Opposed (Or flat) 4

Vee 8

Firing Order: -

1–4–3–2

1–8–4–3–6–5–7–2

Piston Engine Types - Layouts