2. Internal combustion engine

8/14/2019 2. Internal combustion engine

1/75

MTM 3202

Diesel propulsion systems


2/75

Diesel propulsion systems


3/75

INTERNAL COMBUSTION ENGINES


4/75

Course Learning Objective:Course Learning Objective: FamiliarizeFamiliarize

students to the basic cycle and design featuresstudents to the basic cycle and design featuresof modern marine diesel enginesof modern marine diesel engines

Specific Objectives:Specific Objectives:

- Define the theory and principle of Internal Combustion Engine- Define the theory and principle of Internal Combustion Engine

- Describe basic operations of working cycle- Describe basic operations of working cycle

- Identify the engine timing diagram

- Describe differences and advantages of 2S & 4S


5/75

Principle of I.C.E An internal combustion engine is one in

which the fuel is burnt within the engine ->usually of the reciprocating type.

It involve system where combustion of the

fuel and the conversion of the heat energyfrom combustion to mechanical energytakes place within the cylinders (ICE)


6/75

I.C.E. CATEGORIES

Spark ignition engines use gaseous or volatiledistillate fuels -> work on a modified Ottocycle -> operate on the 2 or 4 stroke cycle.

Compression ignition engine use distillateliquid fuels -> work on either 2 or 4 strokecycle and normally designed to operate on thedual-combustion cycle (Otto and Diesel cycle)


7/75

Otto cycle

In the Otto cycle the theoretical pressure

volume diagram is formed from : two constant

volume and two adiabatic processes.

The air in the cylinder is compressed

adiabatically.

Heat is added to the air at constant volume ->

Work is done during the adiabatic expansion

and -> then heat is rejected at constant volume


8/75

Otto Cycle

A B : Adiabatic compression

B C : Heat received at constant volume (combustion)

C D : Adiabatic expansion

D A : Heat rejected at constant volume (exhaust)

P r

e s

s u

r e

(

P

a )

Volume (m3)V1 V2

P1

P2

A

B

C

D


9/75

Otto Cycle

1. The induction stroke takes place at A. Although in theory thepressure should be the same as atmospheric, in practice it's ratherlower. The amount of petrol air mixture taken in can be increased by useof a supercharger.

2. A to B is the compression stroke. Both valves are closed. Thecompression is adiabatic, and no heat enters or leaves the cylinder.

3. Ignition occurs at C. The gases resulting from the ignition expandadiabatically, leading to the power stroke.

4. D to A the gas is cooled instantaneously.

5. At A the exhaust stroke occurs and the the gases are removed atconstant pressure to the atmosphere.

6. Strange as it may seem, the piston does half a revolution at A.Actually it's slightly in practice, as the the valve timing is more complex.


10/75

Diesel cycle

In the diesel cycle the theoretical pressure-

volume diagram is formed from two adiabatic

operations, one constant-pressure and one

constant-volume operation. Air is compressed adiabatically, then heat is

added at constant pressure. Adiabatic expansion

takes place and then heat is rejected at constant

volume


11/75

Diesel Cycle

A B : Adiabatic compressionB C : Heat received at constant pressure(combustion)

C D : Adiabatic expansion

D A : Heat rejected at constant volume

P r

e s

s u

r e

(

P

a )

Volume (m3)V1 V2

P

A

B C

D


12/75

Diesel cycle

1. The induction stroke takes air in ideally at constant volume,pressure at temperature.

2. The compression stroke takes place from A to B. The airis compressed adiabatically to about 1/20 of its original

volume. It gets hot.

3. From B to C fuel is injected in atomised form. It burnssteadily so that the pressure on the piston is constant.

4. From C to D the power stroke moves the piston down asadiabatic expansion takes place.

5. D to A cooling and exhaust occurs.


13/75

Dual cycle

In the dual cycle, air is compressed

adiabatically, then heat is added, partly in

a constant volume process and the

remainder in a constant pressure process.

Expansion takes place adiabatically and

then heat is rejected at constant volume


14/75

P r

e s

s u

r e

(

P

a )

Volume (m3)V1 V2

P

A

B

C D

E

A B : Adiabatic compression

B C : Heat received at constant volume

C D : Heat received at constant pressure

D E : Adiabatic expansion

E A : Heat rejected at constant volume


15/75

COMPRESSION IGNITION

ENGINE Compression ignition engine works on dual cycle

The fresh air enters each of the engine cylinders and iscompressed by the upward movement of the piston.

The compression causes the temperature and pressure ofthe fresh air to increase

Fuel injectors or fuel valve will supply the fuel oil in finespray when the piston is nearly at top dead centre


16/75

The fuel will then be mixed with air (compressed) and

burn inside the cylinder when the piston is at TDC.

The expanding gases on top of the piston (completed

combustion) will push the piston moving it downward and

rotating the crankshaft .

The cycle will be repeated until the engine stops


17/75

Cycle of Operations

Four strokes of CI engine are as

follows:-

Suction Stroke / Induction Stroke Compression Stroke

Explosion Stroke / Power Stroke

Exhaust Stroke


18/75

SUCTION STROKE

In which the air is admitted to the

engine cylinder


19/75

COMPRESSION STROKE

In which the charge of fresh air is

compressed by the piston, and

fuel is injected just before thepoint of maximum compression


20/75

POWER STROKE

In which the air- fuel mixture isignited by the heat produced by

compression of air

The pressure rises due to fuel

combustion and pushes pistondownwards to drive the engine


21/75

EXHAUST STROKE

Exhaust valve opens at the end of

power stroke

The expanded burnt gases are

exhausted / expelled from thecylinder


22/75

The four strokes in duel cycle of CI engine

are completed in two revolutions of the

crankshaft.

There are thus two piston strokes in each

revolution of the crankshaft


23/75

FOUR STROKE ENGINE

INLET VALVE CYLINDER HEAD FUEL INJECTOR

PISTON

CYLINDER

LINER

CRANKSHAFT

DIRECTION

CRANK PIN

INDUCTION STROKE / COMPRESSION STROKE

SCAVENGE STROKE

POWER / EXPANSION STROKE

EXHAUST VALVE

EXHAUST STROKE


24/75

How strokes are executed

Strokes are executed by combination of

valves and gears


25/75


26/75

SUCTION / INDUCTION STROKE

Piston draws air into cylinderduring downward movement orstroke through opened inlet valve.(suction effect)

Exhaust valve and fuel injector areclosed

At the end of the stroke (BDC) theinlet valve close, which inside thecylinder now full with fresh air.


27/75

COMPRESSION STROKE

Stroke begins when the pistonstarts to move upward (fromBDC to TDC).

Inlet valve, exhaust valve andfuel injector remain closed.

The air which is trapped in thecylinder is now compressedrising in temperature


28/75

POWER STROKE Before the piston reaches

TDC(approx.15 20o), thefuel injectors supply fuel oil ina fine spray(end approx. 15-20o after TDC)

The mixture (fuel oil and air)ignites and explodes whilethe piston crosses TDC

High pressure (expansion of

the gases) on top of thepiston push the pistondownward towards BDC


29/75

EXHAUST STROKE

Stroke begins when the piston againstarts to move upward (from BDC toTDC) as in compression stroke,however only exhaust valves areopened.

The exhaust gases are expelled fromthe cylinder through the exhaust valveports.

At the end of the stroke (TDC), the

exhaust valve closes but inlet valve isopened starting the cycle once again


30/75

Power produced

Power produced by a 4-stroke cycle engine in

kW is given as

2

PLANPower=

P= Mean effective pressure, kN/m2

L= Stroke length, m

A= Area of cylinder bore, m2

N= Revolution/second


31/75

4 - STROKE CYCLE

1

7

1

2

3 4 5

6

8

9

10

PRESSURE

DIRECTION

PIST

ON

POSITION

1/7

2

3 45

6

8

9

10

4 - STROKE CYCLE


32/75

1-2 Suction stroke ends 2-3 Compression stroke. Inlet valve closed and

piston moved upwards to compress the

trapped air (Temperature rises). 3-4-5 Fuel injector in operation. Combustion

occurs (mixture of compressed air and fuel) 5-6 Due to expansion of gases piston

moves downward. (Power stroke)

6-7-8 Exhaust stroke. Exhaust valve opens andpiston moves upward removing gases. 8-9-10 Overlapping period: both exhaust and inlet

valves are open. 10-1 Suction stroke piston moves downward.

Exhaust valve closed and inlet valve open. 1- the rest The cycle continues until the

engine stops

4 STROKE CYCLE


33/75

Rotation

SUCTIONSTROKE

COMPRESSIONS

TROKE

POWERS

TROKE

EXHAUST

STROKE

Exh. v/v

opens

Inlet v/v

closes

Inlet v/v

opens

Fuel

injection

begins

Fuel

injection

ends

Exh. v/v

closes

FOUR STROKE TIMING DIAGRAM


34/75

VALVE OVERLAPPING

It can be defined as the period when inlet and exhaustvalve were open at the same time.

E.g., Inlet valve opened before the piston reached TDC at

the end of exhaust stroke, say 20o before TDC.

Exhaust valve remained open and will be closed atcertain degree of the piston movement after TDC,say 20o after TDC.

By providing overlapping period on 4 stroke engine,the residual exhaust gases will be expelled effectively

with the rushing in of fresh air.


35/75

VALVE OVERLAP

OVERLAPPING PERIOD

Inlet v/v

opens

Exh. v/v

closes

TDC


36/75

2-Stroke cycle diesel engines


37/75

Learning Objective:Learning Objective: Know the basic cycleKnow the basic cycle

and design features of modern marine dieseland design features of modern marine dieselenginesengines

Specific Objectives:Specific Objectives:

Describe the operation cycle process of a2-stroke diesel engine.

Identify the 2-stroke engine timing diagram


38/75

The two stroke cycle is so called because

it takes two strokes of the piston or one

revolution of crank shaft to complete the

processes needed to convert the energyin the fuel into work.

TWO STROKE CYCLE


39/75

Why 2-Stroke Cycle Engines

We know 4-stroke cycle engine gives only

one power stroke out of 4 strokes of the

piston or one power stroke in two

revolutions of the crank shaft.

This makes engines power to weight

ratio low mainly because three strokes

consume power against one which

produces


40/75

2S

In the two stroke engine, cycle is completed in two strokes ofthe piston or one revolution of the crankshaft.

Thus out of 3 power consuming strokes of the 4-stroke cycletwo strokes are saved

Engine thus produces one power stroke in every revolution ofthe engine which is two times in comparison to 4-stroke cycle

This improves power to weight ratio of the engine and

reduces its size for same power.


41/75

2-Stroke cycle is achieved by eliminating suction andexhaust strokes of the 4-stroke cycle

In order to eliminate suction and exhaust strokes, somespecial arrangements are required to be provided for:-

-.charging air into cylinder without suction from piston- Exhaust gases must be expelled out of the cylinderwithout assistance from piston

2S


42/75

Inlet air

port

Exst portExst port

Power

stroke CompstrokePiston

PistonInlet air

port


43/75


44/75

The crankshaft is revolvingclockwise and the piston is

moving up the cylinder,compressing the charge ofair.

Because energy is being

transferred into the air,pressure and temperatureincrease.

By the time the piston is near

the top of the cylinder(known as Top Dead Centeror TDC) the pressure is >100bar and the temperature >

500C


45/75

Just before TDC fuel is injectedinto the cylinder by the fuel

injector.

The fuel is "atomised" into tinydroplets. Being very small, thesedroplets heat up very quickly andstart to burn as the piston passesover TDC.

The expanding gas from the fuelburning in the oxygen forces thepiston down the cylinder, turning

the crankshaft.

It is during this stroke that workenergy is being put into theengine; during the upward stroke

of the piston, the engine is having


46/75

As the piston moves down thecylinder, the useful energy

from the burning fuel isexpended.

At about 110 after TDC theexhaust valve opens and thehot exhaust gas (consistingmostly of nitrogen, carbondioxide, water vapour andunused oxygen) begin to

leave the cylinder.


47/75

At about 140 after TDC thepiston uncovers a set of ports

known as scavenge ports.

Pressurized air enters thecylinder via these ports and

pushes the remainingexhaust gas from thecylinder, "scavenging".

The piston now goes pastBDC and starts moving upthe cylinder, closing thescavenge ports. The exhaustvalve then closes and

compression begins.


48/75

1 -2 Compression2 - 3 Fuel Injection

3 - 4 Power

4 - 5 Exhaust Blowdown

5 - 6 Scavenging

6 - 1 Post Scavenging

1. approx 110 BTDC

2. approx 10 BTDC

3. approx 12 ATDC

4. approx 110 ATDC

5. approx 140 ATDC

6. approx 140 BTDC

The two stroke cycle can also be illustrated ona timing diagram.


49/75

1

2

3

4 5 6

7

8

PISTON

POSITION

PRESSURE1

2

3

4 5

6

7

8


50/75

1-2 Scavenging period, both exhaust and inlet portsare open.

2-3 Scavenge stroke ends. Exhaust ports remain open to

ensure only fresh air remains in thecylinder.

3-4 Compression takes place. Both ports closed.

The air is then compressed by the upward movement ofthe piston.

4-5-6 Fuel injector is operational supplying fuel oil. 6-7 Due to expansion of gases, piston moves downward.

(Power stroke)

7-8 When piston crown/top ring passes the exhaust ports,exhaust begins

8-1 When the piston passes the inlet ports, Scavenging beginsand fresh air fills the cylinder, thus pushing the remaining exhaustgases out


51/75

Rotation

Fuel

injection

begins

Fuel

injection

ends

SCAVENGE

COMPRESSION P

OWERSTRO

KE

EXHAUST

Scavenge

ports

open

Scavenge

ports

close

Exhaust

ports

open

Exhaust

ports

close

TWO STROKE TIMING DIAGRAM


52/75

The 2 strokecrosshead engine

works on exactlythe same principleand cycle as the 2stroke trunk piston

engine.
http://www.marinediesels.info/2_stroke_crosshead_engine_access.htm


53/75

The disadvantages of the two stroketrunk piston engine are that:

It has a low overall height, lubricatingoil splashed up from the crankcase tolubricate the liner can find its way intothe scavenge space, causing foulingand a risk of fire.

There is also the likelihood of liner andpiston skirt wear, allowing air into thecrankcase. This can supply therequired oxygen for an explosionshould a hot spot develop.

The crankcase oil must have additiveswhich can cope with contaminationfrom products of combustion, and theacids formed during combustion due tothe sulphur in the fuel.

The majority of 2 stroke engines encountered at sea are of the "crosshead" type.In this type of engine the combustion space (formed by the cylinder liner piston


54/75

In this type of engine the combustion space (formed by the cylinder liner, pistonand cylinder head), and the scavenge space are separated from the crankcase bythe diaphragm plate.

The piston rod is bolted to the piston and passes through a stuffing box mounted

in the diaphragm plate. The stuffing box provides a seal between the two spaces,stopping oil from being carried up to the scavenge space, and scavenge air leakinginto the crankcase.

The foot of the piston rod is bolted to the crosshead pin. The top end of theconnecting rod swings about the crosshead pin, as the downward load from theexpanding gas applies a turning force to the crankshaft.

To ensure that the crosshead reciprocates in alignment with the piston in thecylinder, guide shoes are attached either side of the crosshead pin. These shoesare lined with white metal, a bearing material and they reciprocate against thecrosshead guides, which are bolted to the frame of the engine. The crossheadguides are located in-between each cylinder.

Using the crosshead design of engine allows engines to be built with very longstrokes - which means the engine can burn a greater quantity of fuel/stroke anddevelop more power. The fuel used can be of a lower grade than that used in atrunk piston engine, with a higher sulphur content, whilst high alkalinity cylinderoils with a different specification to that of the crankcase oil are used to lubricate

the cylinder liner and piston rings and combat the effects of acid attack.


55/75

SCAVENGING

To ensure a sufficient supply of fresh air forcombustion by removing all remaining exhaust gasesby blowing with these fresh air.

Supercharging is a large mass of air that is supplied tothe cylinder by blowing it in under pressure either byelectrically driven auxiliary blower or exhaust gasdriven turbocharger.

The flow path of the scavenge air is decided by theengine port shape and design and the exhaustarrangements.


56/75

SCAVENGING PERIOD

It can be defined as a period when inlet and exhaustare open at the same time:

Remaining exhaust gas will be expelled from thecylinder through exhaust ports or exhaust valve (if

fitted).

Fresh air which has collected in the scavenge

manifold rush into the cylinder Scavenging period: Normally when piston is at

BDC,(or as per maker or engine design or the location of the portsitself)


57/75

SCAVENGING METHODS

CROSS/DIRECT FLOW SCAVENGING

LOOP SCAVENGING

UNIFLOW SCAVENGING

C / f


58/75

Cross/direct flow

scavenging

Exhaust

manifold

Scavenge

manifold


59/75

Loop scavenging

Exhaust

manifold

Scavenge

manifold

2 stroke engines do not have exhaust


60/75

2 stroke engines do not have exhaustvalves; With scavenge ports in the cylinderliner, they are fitted with exhaust portslocated just above the scavenge ports.

As the piston uncovers the exhaust ports onthe power stroke, the exhaust gas starts toleave the cylinder.

When the scavenge ports are uncovered,scavenge air loops around the cylinder andpushes the remaining exhaust gas out ofthe cylinder.

This type of engine is known as a loop

scavenged engine. Note that the pistonskirt is much longer than that for a uniflowscavenged engine. This is because the skirthas to seal the scavenge and exhaust portswhen the piston is at TDC.


61/75

TWO STROKE ADVANTAGES

Compactness in relation to the power output. Not requiredto increase brake mean effective pressure or the engine

speed to increase rating.

(High bmep increases the stresses on engine components,

greater rate of cylinder wear, whilst the alternative of higherspeed, valve flutter may become a serious problem)

Each out-stroke being a working stroke gives more even

turning for the same number of cranks, consequently a

lighter flywheel may be employed. The reversing operation of rotation is simplified since there

is less valve gear to contend with.


62/75

OTHER ADVANTAGES

Fewer moving parts and lower maintenance Lower specific fuel consumption

No gear loss

Simplicity in construction Longer life time

Higher reliability (product)

Low lubricating oil consumption Better ability to burn low quality fuel oil


63/75

Good volumetric efficiency, good combustioncharacteristic and positive exhaust scavenging.

The thermal and mechanical efficiencies are

slightly better than 2S engine. Only half the quantity of the heat generated in

the cylinders has to be dealt within a given time,so that efficient lubrication of the piston and

cooling of the cylinder is more easilyaccomplished.

FOUR STROKE ADVANTAGES


64/75

Lower initial cost for equivalent power Ease ofinstallation

Lowerweight per unit power

Saving in weight and engine room length

Increased cargo capacity

Free choice ofpropeller speed through

gearing

Suitable forelectrical powertake off

OTHER ADVANTAGES


65/75

Supercharging/Turbocharging

Process of pushing a higher pressure air

charge into the cylinder greater than

atmospheric pressure, so that extra mass

of air can be delivered into cylinder to burnmore fuel and produce extra power.

Turbocharging can increase power output

of engine by 60%


66/75

Turbocharging

Very effective pressure charging.

Utilizes 20% of waste heat in exhaust gas

which contains 35% of fuel heat.

How?


67/75

By increasing mass of air in cylinder, more fuel can beburned and correspondingly power output will be

increased

Various methods can be adopted:Electrically powered auxiliary blower

Utilization of heat energy from exhaust gas todrive a single stage impulse turbine directly coupled toa simple blower (free running unit) called exhaust gasturbocharger

Turbocharger utilizes free energy of exhaustgases and hence improves efficiency of the engine

Typical heat balance of an


68/75

Typical heat balance of an

engineUseful Output (Brake Power) 34%

Cooling Loss 30%

Exhaust Loss 26%

Friction, Radiation, etc. 10%

-------

Total Heat Input100%


69/75

TurbochargerSystem

Advantages


70/75

Advantages

Increased power for an engine of the same size

OR reduction in size for an engine with thesame power output.

Reduced specific fuel oil consumption ->

mechanical, thermal and scavenge efficienciesare improved due to less cylinders, greater airsupply and use of exhaust gasses.

Thermal loading is reduced due to shorter moreefficient burning period for the fuel leading toless exacting cylinder conditions.


71/75


72/75

Risk

Crankcase explosion

Scavenge fire


73/75

Design consideration

Types of fuel and fuel oil system design Types of lubricating oil and lubricating oil systems

Cooling systems

Waste heat utilization systems

Intake and exhaust valve systems Starting air systems

Instrumentation system

Control and automation system

Installation items

Safety features


74/75

Summary

Principle of ICE

Theoretical Cycles

Basic principle of operations of working cycle

Cycle & Timing Diagram

Principles of Scavenging & Arrangements

Advantages of 2S & 4S

Structural differences

Overlap of Inlet & Exhaust


75/75

References

Introduction to Marine Engineering,

Marine Engineering , Roy L. Harrington, SNAME, 198

El-Hawary, F. (2001). Ocean Engineering Handbook. CRC

Press, UK.

Calder, Nigel (2007): Marine diesel engine: maintenance,

troubleshooting and repair.

Documents

2. Internal combustion engine