Diesel Power Plant

D1MC Semester 2 / ECS / March 2007/LSC /Marine Diesel Engine Power Plants 1

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Diesel Power Plant

The most popular and

widely used power

plant on merchant

ships.



Module Objectives

1

• Know various types of int. combustion engines

• Describe marine 2-S & 4-S diesel engines

2

• Describe common piping systems for diesels

• Describe Scavenging & powering

3

• Describe Scavenge fires and crankcase explosions

• Know operational issues related to diesels.



Internal Combustion Engines (I.C.E)

2-S

&

4-S

C.I

&

S.I

Slow & Medium Speed



Diesel Engines

• Combustion of fuel takes place inside the engine.

• In Diesel Engines, air in the cylinder is compressed to a high pressure so that it attained a high temperature.

• The oil fuel is injected into this high temperature air and the fuel immediately ignites. The engine is classed as compression ignition engine.

• In Petrol engines, the fuel is most often ignited by an electric spark.



Internal Combustion Engines

• Combustion of fuel takes place inside the engine.

• In Diesel Engines, air in the cylinder is compressed to a high pressure so that it attained a high temperature.

• The oil fuel is injected into this high temperature air and the fuel immediately ignites. The engine is classed as compression ignition engine.

• In Petrol engines, the fuel is most often ignited by an electric spark.



Theoretical Diesel Engine Cycle



Four Stroke Diesel Engine

• It takes four strokes of the piston (two revolution of crankshaft) to complete one working cycle.

• Induction stroke: Piston moving down, air inlet valve opens and air drawn into cylinder.

• Compression stroke: Piston moving up, no valves are opened. Air is compressed in cylinder.

High temperature air ignites the fuel injected.

• Power stroke: Piston moving down during combustion period of high pressure.

• Exhaust Stroke: Piston moving up, exhaust valve opened and exhaust gases expelled from cylinder.



Four Stroke Diesel Engine



Four Stroke Timing Diagram



Two Stroke Diesel Engine

• It takes two strokes of the piston to complete one working cycle or one revolution of crankshaft.

• Every downward stroke is a power stroke, and every upward stroke is a compression stroke.

• Exhaust of the burned gases from the cylinder happens during late period of downward stroke.

• Fresh charged air is taken in during early part of upward stroke.

• Scavenge air clean out the cylinder by pushing the exhaust gases out leaving a clean charge air.



2-S slow speed diesel engine





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Gas Exchange Process

• Scavenging is the removal of exhaust gases by blowing in fresh air

• Charging is the filling of cylinder with a supply or charge of fresh air ready for compression.

• Supercharging is the supply of large mass of air into the cylinder by blowing it in under pressure.

• Modern engines make use of exhaust gas driven turbochargers to supply pressurised fresh air for scavenging and supercharging.









Scavenging Process

Cross-flow Scavenging

• Incoming air is directed upwards, pushing the exhaust gases before it.

•Exhaust gases travel down and out of ports.

Advantages/Disadvantages

• Requires fitting piston skirt to prevent escape of air/exhaust from ports.

CROSS



Scavenging Process

Loop Scavenging

• Incoming air passes over the piston crown then rises towards the cylinder head.

• Exhaust gases are forced before the air passing out of ports.


• Temperature differential is high along port areas of liner materials.

LOOP



Uniflow Scavenging

• Incoming air enters at the lower end of the cylinder and leaves at the top


• Most efficient scavenging system.

• Requires exhaust valves, more maintenance & cost.

Scavenging Process



Scavenging Process



Scavenging Process



Slow Speed Diesel Engine



Diesel Engines

Slow Speed Engines

• Engines in the range of 100 to 120 rev/ min.

• It is used for main propulsion since it can be directly coupled to propeller and shafting.

• It provides high power, can burn low grade fuel, and has high thermal efficiency.

• Cylinders and crankcase are isolated, which reduces contamination.

• Special lubricating oils is used for crankcase and cylinders.



Engine in the range of 250 to 750 rev./min.

• Medium speed four stroke engines provide better power –weight ratio power –size ratio ( vee engines).

• Lower initial cost of equivalent power.

• Higher speed requires use of gearbox (for low speed drive)

and flexible couplings ( damped out vibration) for main propulsion (coupling situated between engine & gearbox).

• There is often a need for a clutch to disconnect the engine from gearbox

• Better quality fuel is necessary because of the higher engine speed.

Medium Speed Engines



Medium Speed Engine



Medium Speed Engine



Marine diesel engines

• Can you state what are the important

systems of the diesel engine.

• 1 ……..

• 2 ……..

• 3 ………

• 4 ………



Fuel Oil System



Lubricating Oil System



Fresh Water System



Starting Air System



Engine Indicator



Engine indicator in a boxspringsIndicator

Coupling

drum



Indicator Diagrams





Indicator Diagrams



Indicated power

The Indicated Power developed in the cylinder is given by:

Indicated Power = P. L. A. N

where P = mean effective pressure

L= length of stroke

A= Area of the bore of cylinder

N= number of power strokes per

second.



Power calculation• If the particulars of the diesel engine are:-

• Diameter of bore = 600 mm

• Stroke length = 2.4 m

• RPM = 90

• Engine cycle = 2 stroke

• No of units = 6

• Spring constant = 2 bar / mm

Calculate the indicated power of the engine.15758 kw,



Calculation of Indicated power

• The 2-stroke main engine of the M.V Seroja has 10 units of bore 900 mm and stroke of length 2.7 m. During a power assessment exercise when the engine speed is 120 rpm, the average area of the indicator diagram is 200 mm2. the length of the indicator diagram is 70 mm. the spring constant used is 2 bar/mm.

• Calculate the indicated power developed by the main engine during that time.19630 KW



Scavenge Fire

• Causes: accumulation of oil and carbon; flame (heat);

air (oxygen) - ignition of oil mixture.

•Indications: excessive black smoke; high exhaust

temperature; loss of engine power

•Action to take: Slow down engine; fuel on unit shut off;

increase cylinder lubrication to unit.

•For persistence fire, engine must be stopped.

•Effect on engine: piston seizure; cylinder liner crack;

distortion of connecting rod



Slow Speed Diesel Engine



Crankcase ExplosionCauses of crankcase explosion

• Hot spot arise from overheated part within or adjacent to the crankcase of an operating engine.

• This hot spot will come in contact with the lubricating oil and the oil will be evaporated.

• The oil vapour will circulate to cooler part of crankcase and condense to form white mist oil particles well mixed with air.

• If this combustible oil mist is circulated back to the hot spot, it will be ignited and a crankcase explosion will take place.



Crankcase ExplosionHow to dealt with

• In the event of a hot spot is detected the engine must be slowed down immediately, and stopped.

• This is to allow the hot spot to cool down .

• Operate the turning gear, with indicator cocks open, to prevent seizure of overheated parts

• Personnel should avoid the vicinity of crankcase door.

• Safety devices fitted: Crankcase oil mist detector, Crankcase explosion relief valve, inert gas flooding system.



Preparing Engine for Stand –By for

departure• Start boiler for heating of cooling medium.

• Warm-up cooling system ( e.g L.O; F.W)

• Turn Main engine with indicator cocks open.

• Lubricate liner with cylinder oil manually.

• Disengage turning gear after turning engine.

• Blow through engine with starting air

• Test engine on fuel for normal running (ahead. & astern) – check critical speed.

• Test steering gears and telegraph



Critical Speed

• The speed of the engine in revolution per minutes at

which resonance condition occurs.

• Resonance condition is when the frequency of applied

forces is very near to or the same as the natural

frequency of the elastic system.

• This causes the amplitude of vibration increases at an

alarming rate and early failure of resonance parts.

• Barred speed-range is the range of speed where high

unsafe stresses occurs before and after the critical

speed.

• Engine must not be continuously operated at speeds

within barred speed range (marked red on tachometer ).



Q & A session

• Thank you

• Please take a look at the LG for

some sample questions.





Sample key questions

• Describe the two / four stroke cycle engine

• Explain the gas exchange process that

occurs during each cycle.

• Describe the type of scavenging process –

loop, cross and uniflow;

• Sketch and describe the LO / JCW / Fuel oil

system.



Sample key questions

– Describes the procedure to prepare the

marine diesel engine for stand-by.

– Explain how a scavenge fire occurs and how

it is tackled.

– Describe how a crankcase explosion occurs

and how it is prevented























Power calculations

Q1- The cylinder diameter of an eight unit, single acting, four

stroke diesel engine is 750mm and stroke is 1125 mm. The

indicated mean effective pressure is 1172 kN/m2, when the

engine is running at 110 rpm. Calculate the indicated power and

brake power , if the mechanical efficiency is 86%. (4271.6 kw, 3673

kw)

Q2 – the area of the indicator diagram, taken from one unit of a

six unit 2-stroke diesel engine is 480mm2. Length of the

diagram is 72 mm. Spring scale is 1 mm = 1.5 bar. Cylinder

diameter is 900 mm, stroke is 1800mm. If the engine is running

at 100 rpm, calculate the indicated power developed by the

whole engine. (11,478kw)

Documents

Diesel Power Plant