Ship Power Plant

Faculty of Engineering Naval Architecture and Marine Engineering Department

MR351 - Ship Propulsion Systems Third Year

Prepared By: Dr. Mohamed Morsy El-Gohary Eng. Hossam Ahmed El-Sherif

Course Contents Subject

Page No.

1. Introduction 2. Review of main machinery

1 6

3. Transmission system

43

4. Propulsors

60

5. Fuel types in marine field

71

6. Marine diesel engines

87

7. Unit conversion factors

137

References 1. Marine Engineering, SNAME, 1992 2. Introduction to marine engineering 2 nd ed., Taylor, 1996 3. Pounder’s marine diesel engines and gas turbines 8th ed., 2004 4. Design of propulsion and electric power generation systems, IMarEST, 2002

Introduction Ship propulsion system is that part of marine engineering concerned by the design and/or selection of main propulsion plant equipments and machineries. The main role of this plant is to produce enough power to overcome the ship resistance and to generate the needed electric power for the various applications onboard the ship (lighting, control systems, pumps, navigation equipments, HVAC, etc).

The above figure shows the main two forces considered in propulsion system; the resistance of the water to the ship motion (R) and the thrust developed by the propeller (T). When considering only the engine room area, the various powers from the engine to the propeller are showed as follows.

Ship propulsion systems

1

Where: BHP = brake horsepower DHP = developed horsepower EHP = effective horsepower ηGB = gearbox efficiency (1% ~ 3%) ηshaft = shafting efficiency (1% ~ 2%) ηP = propeller open water efficiency (30% ~ 60%) The following relations link these terms together:

EHP =

R · V c

V = ship speed c = units conversion constant

QPC =

EHP DHP

QPC = Quasi-Propulsive Coefficient

QPC =

ηH

·

η RR

·

ηP

ηH = hull efficiency = EHP/THP (THP = Thrust horsepower) ηRR = Relative Rotative efficiency DHP BHP =

η shaft

·

η GB

The thrust developed by the propeller is linked to the ship resistance by the following formula: R = T . (1 – t) t = thrust deduction fraction

Ship propulsion systems

2

The thrust deduction fraction is a parameter related to the ship design and it is related to another parameter which is the wake fraction ω.

Example Given the following ship particulars, find the required engine brake power. Ship speed V=20 knots Thrust=40 tonnes Wake fraction ω=0.3 Thrust deduction fraction t=0.6*ω Quasi-propulsive coefficient QPC=0.68 Transmission efficiency ηt=0.95 Solution

t = 0.6 x 0.3 = 0.18 R = T x (1 - t)=40 x (1 - 0.18) = 32.8 tonnes EHP =

EHP =

R · Vs c 32800 · 20 · 0.514 75

EHP = 4496 DHP=EHP/QPC=4496/0.68=6611 HP BHP=DHP/ηt=6611/0.95=6960 HP BHP=6960

Ship propulsion systems

3

The main components of a propulsion system are shown on the next diagram: Prime Mover (Power Plant)

Transmission

Propulsor

Prime mover: The function of the prime mover is to deliver mechanical energy to the propulsor. The prime mover may be one of the following: • Diesel engine • Gas turbine • Steam turbine • Electric motor The diesel engine is the most common prime mover in the merchant marine, mainly due to its low fuel consumption in comparison with other prime movers. Gas turbines find their application in fast and advanced ship types and naval vessels. The power to weight ratio of gas turbines is higher than that of diesel engines. Some ship types, such as naval vessels and LNG carriers may have a steam turbine as propulsion engine. Two kinds of steam plants can be distinguished in marine applications: fossil-fired steam plants and nuclear steam plants. Fossil-fired steam plants are frequently found on board naval vessels and LNG carriers. Submarines and aircraft carriers may be equipped with nuclear steam plants. ice-breaking vesselspower especially in Russian arcticSome areascommercial were provided with nuclear plants since these vessels may stay for months in sea. Electric motors found their way as prime mover in the 90’s; they are used with electric generation plant combined of an engine (one of the above types) and an electric generator. They are mainly found in advanced passenger ships, some new designs of offshore support vessels (OSV) are intended to use electric motors especially for dynamic positioning applications.

Ship propulsion systems

4

Transmission: Transmission is a sub-system of the propulsion system. It is a system itself built up from components such as shafts, gearboxes and bearings. The transmission’s functions are: 1. To transfer the mechanical energy generated from the prime mover to the propulsor 2. To transfer the thrust generated by the propulsor to the ship’s hull The latter is done by means of a thrust bearing; a component that is found in every transmission system. Tow types of transmission are used: • •

Direct: the prime mover is coupled directly, through a shaft to the propulsor (this is the case with low speed diesel engines) Geared: the prime mover delivers its energy through a gearbox and a shaft to the propulsor. The function of the gearbox is to reduce the rotational speed of the engine to match the desired rotational speed of the propulsor.

Propulsor: The propulsor converts the rotating mechanical power delivered by the engine into translating mechanical power to propel the ship. The most common propulsor is the propeller. In general, two types of propeller are distinguished, fixed pitch and controllable pitch propellers. Other types of propulsors are for example, waterjets and Voith-Schneider propulsors (vertical axis propeller).

Ship propulsion systems

5

Review of main machinery In this chapter we will make a brief review of the main types of prime movers stated before; diesel engines, gas turbines, steam plants, electric plants. From now on, these types will be named power plants, i.e. diesel power plant, gas power plant, etc, since the whole engine room arrangement is affected by the type of prime mover installed.

Power plant concepts The ship’s engine room may contain more than one type of prime movers, in this case the power plant will be called combined, and this makes the basic types of power plants as follows: • Diesel power plant • Gas turbine power plant • Steam power plant • Nuclear power plant •

Combined power plant

1. Diesel power plant 1.1 Overview The diesel engine is reciprocating internal combustion engine. Diesel engines are used to drive cars, trains ships and other marine structures, electric generators, pumps, compressors, etc. The diesel engine is still the most frequently used prime mover in the merchant marine field. Power ranges between 0.25 MW for the smallest high speed engines to 90 MW for the for the biggest lowspeed engines. The main advantages of diesel engines are: • It is relatively insensitive to fuel quality; it can be operated by light fuel as well as the heaviest residual fuels. • High reliability • High maintainability due to simple technology • High efficiency, can reach more than 50% • Low cost, in terms of initial and operational costs.

Ship propulsion systems

6

While the main disadvantages of diesel engines are: • Pollutant emissions • Low power to weight ratio if compared with gas turbine • Vibration and noise From the application viewpoint, three main types of diesel engines are available: • Low speed diesel engines (rpm