IC ENGINES

THERMODYNAMIC CYCLE Any thermodynamic cycle is

essentially a closed cycle in which, the working substance undergoes a series of processes and is always brought back to the initial state.

NEED TO STUDY

Design of new cycle

Improve the existing cycle

A.ABUBAKKAR / DEPARTMENT OF MECHANICAL ENGINEERING

THERMODYNAMIC CYCLE

HEAT ENGINE CYCLE

OR POWER CYCLE HEAT PUMP CYCLE

OR REFRIGERATION CYCLE

GAS POWER

CYCLE

VAPOR POWER

CYCLE

Otto cycle

Diesel cycle

Dual cycle

Brayton cycle

Rankine cycle


ENGINE TERMINOLOGY


ENGINE TERMINOLOGY


ENGINE TERMINOLOGY ( Contd. )

• Clearance volume

• Stroke volume

• Bore

• Stroke

• Top Dead Centre

• Bottom Dead Centre


ENGINE TERMINOLOGY ( Contd. ) Stroke

Distance travelled by the piston from one extreme position to the other.

Bore

It is defined as cylinder diameter or piston face diameter; piston face

diameter is same as cylinder diameter.

Swept volume/Displacement volume

Volume displaced by the piston as it travels through one stroke.

Bottom Dead Center (BDC)

Position of the piston when it stops at the point closest to the

crankshaft.Also called as Crank End Dead Center (CEDC)

Top Dead Center (TDC)

Position of the piston when it stops at the furthest point away from the

crankshaft.


ENGINE TERMINOLOGY ( Contd. )

combustion pressureconstant before Volume

combustion pressureconstant after Volume ρ , ratio offCut

combustion olumeconstant v before Pressure

combustion olumeconstant vafter Pressure α , ratioexplosion or ratio Pressure

expansion before Volume

expansion after Volumer , ratioExpansion

ncompressioafter Volume

n compressio before Volumer , ration Compressio

e


THERMODYNAMIC CYCLE

Vapour power cycles in which the working

fluid undergoes a phase change during the cyclic

process.

Gas power cycles in which the working fluid

does not undergo any phase change.


HEAT ENGINE


P – V- T RELATION

1

1

2

2

1

1

2

TT

VV

PP

n

n

n


CLASSIFICATION OF

IC ENGINE

IC ENGINE CLASSIFICATION

Engines may be classified on the basis of 1. Number of strokes

2. Thermodynamic cycle

3. Number of cylinders

4. Ignition system

5. Cooling system

6. Fuel Used

7. Fuel supply system

8. Lubrication system

9. Cylinder arrangement


IC ENGINE CLASSIFICATION(Contd.)

1. Number of strokes

2 stroke

4 stroke

2. Thermodynamic cycle

Otto cycle

Diesel cycle

Dual cycle

3. Number of cylinders

Single cylinder

Multi cylinder

4. Ignition system

battery coil

Magneto ignition


IC ENGINE CLASSIFICATION (Contd.)

5.Cooling system

Water cooled engines

Air cooled engines

6. Fuel Used

Petrol engine

Diesel engine

Gas engine

Bi fuel engine

7. Fuel supply system

Carburettor engines

Solid injection engines



8.Lubrication system

Wet sump lubrication

Dry sump lubrication

Mist lubrication

9.Cylinder arrangement

In line engine

V engine

Radial engine

Opposed piston






IC ENGINE COMPONENTS AND

FUNCTIONS

IC ENGINE


IC ENGINE


IC ENGINE COMPENENTS

Cylinder Head

The piece which closes the end of the cylinders,

usually containing part of the Clearance volume of

the combustion chamber.


IC ENGINE COMPENENTS(Contd.)

Cylinder Block

Body of the engine containing cylinders, made of cast iron or

aluminum.



Piston

A movable part fitted into a

cylinder, which can receive and

transmit power.

Combustion chamber

The end of the cylinder

between the head and the

piston face where combustion

occurs.



Piston rings

They fit into circumferential

grooves around the piston and

form a sliding surface against the

cylinder walls.



Connecting rod Rod connecting the piston with the rotating crankshaft, usually made of steel

or alloy forging in most engines but may be aluminum in some small engines.



Crankshaft

Rotating shaft through which engine work output is supplied to external

systems



Crankcase

Part of the engine block surrounding the crankshaft.

Flywheel

Rotating mass with a large moment of inertia

connected to the crank shaft of the engine. The

purpose of the flywheel is to store energy and

furnish large angular momentum that keeps the

engine rotating between power strokes and smooths

out engine operation.




Camshaft

Rotating shaft used to push

open valves at the proper

time in the engine cycle,

either directly or through

mechanical or hydraulic

linkage .

Cam Lobe

It changes rotary motion

into reciprocating motion


Push rods

The mechanical linkage between the camshaft and valves on overhead valve engines with the camshaft in the crankcase.

Intake Valve

It lets the air or air fuel mixture to enter the combustion chamber.

Exhaust Valve

It lets the exhaust gases escape the combustion Chamber.

Valve Springs

It keeps the valves closed.




Spark plug

Electrical device used to initiate combustion in an SI engine by creating

high voltage discharge across an electrode gap.


Intake manifold

Piping system which delivers incoming air to the

cylinders, usually made of cast metal, plastic, or

composite material.

Exhaust manifold

Piping system which carries exhaust gases away

from the engine cylinders, usually made of cast

iron.



Fuel injector

A pressurized

nozzle that

sprays fuel into

the incoming air

in CI engines .


IC ENGINE COMPENENTS(Contd.) Fuel pump

Electrically or mechanically driven pump to supply fuel from the fuel

tank (reservoir) to the engine.

Carburettor

A device which meters the proper amount of fuel into the air flow by

means of pressure differential.


TWO STROKE ENGINE


FOUR STROKE ENGINE



FOUR STROKE CYLINDER ENGINE TWO STROKE CYLINDER ENGINE

1. For every two revolution of the crank shaft,

there is one power stroke.

2. Because of the above, turning moment is

not so uniform and hence heavier flywheel is

needed.

3. For the same power more space is required.

4. Because of one power stroke in two

revolutions, lesser cooling and lubrication

requires. Lower rate of wear and tear.

5. Valves are required – inlet and exhaust

valves.

6. Because of heavy weight, complicated valve

mechanism and water cooled, making it

complicated design and difficult to maintain.

7. The air-fuel mixture is completely utilized

thus efficiency is higher.

8. Volumetric efficiency is high due to more

time for induction.

9. Lower fuel consumption per horse power.

10. Used in heavy vehicles, e.g. Buses, lorries,

trucks etc.

11. The engine cost is more.

1. For every one revolution of the crank shaft,

there is one power stroke.

2. Because of the above, turning moment is

more uniform and hence a lighter flywheel is

used.

3. For the same power less space is required.

4. Because of one power stroke for every

revolution, greater cooling and lubrication

requirements. Higher rate of wear and tear.

5. Ports are made in the cylinder walls – inlet,

exhaust, and transfer port.

6. Simple in design, light weight and air cooled

and easy to maintain.

7.The exhaust gases are not always completely

removed. This cause lower efficiency.

8. Volumetric efficiency is low due to lesser

time for induction.

9. The fuel consumption per horse power is

more because of fuel dilution by the exhaust

gas.

10. Used in light vehicles, e.g. Motor cycle,

scooter, etc.

11. The engine cost is less.


S.I. ENGINES C.I. ENGINES

1. The fuel used is gasoline (Petrol).

2. Air + Fuel mixture is taken during

suction.

3. For mixing air and fuel a separate

device called carburettor is required.

4. Since homogeneous mixture is

produced in carburettor, no need of

injector.

5. Pressure at the end of compression is

about 10 bar.

6. A spark plug is used to ignite the air fuel

mixture.

7. Self ignition temperature of fuel is not

attained. In other words, the fuel is not

self ignited.

8. S.I. Engines works on Otto cycle (i.e)

combustion takes place at constant

volume.

1. Fuel used is Diesel.

2. Only air taken during suction.

3. No need of carburetor.

4. For atomizing and spraying the fuel

inside the cylinder, fuel injector is

necessary.

5. Pressure at the end of compression is

about 35 bar.

6. Spark plug is not necessary.

7. The fuel get ignited due to the high

temperature of compressed air.

8. C.I. Engines works on diesel cycle (i.e)

combustion takes place at constant

pressure.


S.I. ENGINES C.I. ENGINES

9. Compression ratio is around 6 to 10.

10. Cold starting of engine is easy.

11. These are very lighter.

12. Vibration is less.

13. Engine weight / kW is less.

14. Less maintenance.

15. thermal is about 25%.

16. Generally employed for light duty

vehicles e.g. two wheeler etc.

17. Spark plug needs frequent

maintenance.

18. Noiseless operation due to less

compression ratio.

9. Compression ratio is around 15 to 25.

10. Cold starting of engine is difficult.

11. Heavier engine.

12. More vibration is there.

13. Engine weight / kW is more.

14. High maintenance is needed.

15. thermal is about 35 to 45%.

16. Generally employed for heavy duty

vehicles e.g. trucks, buses, etc.

17. Fuel injector needs less maintenance.

18. Very noisy operation due to high

compression ratio.

VALVE TIMING DIAGRAM


THEORETICAL VALVE TIMING DIAGRAM FOR 4

STROKE PETROL ENGINE

ACTUAL VALVE TIMING DIAGRAM


FOR 4 STROKE DIESEL L ENGINE FOR 4 STROKE PETROL ENGINE

PORT TIMING DIAGRAM

PORT TIMING DIAGRAM OF DIESEL ENGINE


PORT TIMING DIAGRAM OF PETROL ENGINE


IGNITION SYSTEM

IGNITION SYSTEM

• Charge of air and petrol fuel will be ignited by means of

the spark produced by means of spark plug.

• The ignition system does the function of producing the

spark in case of spark ignition engines.

• Basically Convectional Ignition systems are of 2 types :

(a) Battery or Coil Ignition System

(b) Magneto Ignition System


BATTERY IGNITION SYSTEM

• Battery

• Ignition coil

• Ignition switch

• Contact breaker

• Condenser

• Distributor

• Spark plug



• The ignition coil steps up 12 volts (or 6 volt) supply to a very high voltage which may range from 20,000 to 30,000 volts.

• A high voltage is required for the spark to jump across the spark plug gas. This spark ignites the air-fuel mixture as the end of compression stroke.

• The rotor of the distributor revolves and distributes the current to the four segments which send the current to different spark plugs.



• When ignition switch in turned on, the current flows from battery to the primary winding. This produces magnetic field in the coil. When the contact point is open, the magnetic field collapses and the movement of the magnetic field induces current in the secondary winding of ignition coil. As the number of turns in secondary winding are more, a very high voltage is produced across the terminals of secondary.

• The distributor sends this high voltage to the proper spark plug which generates spark for ignition of fuel-air mixture. In this way, high voltage current is passed to all spark in a definite order so that combustion of fuel-air mixture takes place in all cylinders of the engine.

• A ballast register is connected in series in primary circuit to regulate the current. At the time of starting this register is bypassed so that more current can flow in this circuit.



Advantages

• Low initial cost.

• Better spark at low speeds and better starting than magneto system.

• Reliable system.

• No problems due to adjustment of spark timings.

• Simpler than magneto system.

Disadvantages

• Battery requires periodical maintenance.

• In case of battery malfunction, engine cannot be started.


MAGNETO IGNITION SYSTEM



• This system consists of a magneto in place of a battery. The magneto consists of a fixed armature having primary and secondary windings and a rotating magnetic assembly. This rotating assembly is driven by the engine.

• Rotation of magneto generates current in primary winding having small number of turns. Secondary winding having large number of turns generates high voltage current which is supplied to distributor. The distributor sends this current to respective spark plugs.



Advantages

• Better reliability due to absence of battery and low maintenance.

• Better suited for medium and high speed engines.

• Modern magneto systems are more compact, therefore require less space.

Disadvantages

• Adjustment of spark timings adversely affects the voltage.

• Burning of electrodes is possible at high engine speeds due to high voltage.

• Cost is more than that of magneto ignition systems.


LUBRICATION SYSTEM

LUBRICATION SYSTEM

Mist lubrication

Wet Sump lubrication system

• Splash and circulating pump system

• Splash and pressure system

• Full Force feed system

Dry Sump lubrication system


SPLASH

LUBRICATION


SPLASH AND CIRCULATING PUMP SYSTEM


SPLASH AND PRESSURE SYSTEM


FULL FORCE FEED SYSTEM


DRY SUMP LUBRICATION


COOLING SYSTEM

COOLING SYSTEM

• The peak temperature that occurs during combustion in internal combustion engines varies from 1500C to 2000C. This large amount of heat produced due to fuel combustion is absorbed by the piston, cylinder head and cylinder walls.

• The internal combustion engine at best can transform only 30% of the heat generated by burning the fuel in to useful work. About 30% has to be removed by the cooling system and the reminder by the exhaust and lubrication systems.

• What ever may be the amount of heat carried away by the coolant, it must be noted that it is a dead loss, because not only no useful work can be obtained from it, but a part of engine power is also used to remove this heat. Therefore it goes without saying that heat loss must be kept minimum by the designer.


NECESSITY OF ENGINE COOLING SYSTEM

• The high temperature reduces the strength of the materials used for piston and piston rings.

• The large temperature differences between the engines parts may cause unequal expansion, resulting in cracking of the parts and thereby the engine failure.

• At high temperature, the lubricating oil may be heated up to such an extent heat decomposition of lubricating oil occurs and viscosity changes may render it unfit for effective lubrication.

• At high temperatures, the lubricating may even evaporate and burn, injuring position and cylinder surfaces. Piston seizure due to overheating, resulting form the failure of the lubrication is quite common.

• The overheating causes excessive thermal stresses in the engine parts, which may load to their distortion. The overheating may cause burning of valves and valve seats.In petrol engines, the pre-ignition of the charge is possible, if the ignition parts initially are at high temperature.The overheating reduces the efficiency of the engine.


AIR COOLING


WATER COOLING

• In this system the circulation of water is due to difference in temperature of water. So in this system pump is not required but water is circulated because of density difference only.


WATER COOLING

• In this system circulation of water is obtained by a pump. This pump

is driven by means of engine output shaft through V-belts.


WATER COOLING OF A 4-CYLINDER

ENGINE

Documents

IC ENGINES