Comparison Between Petrol and Diesel Engine & Engine Overview.

Engine is something which converts the Heat Energy into Mechanical Energy, it can be said as a device which is provides power to machine to do the specific work.
Heat engine is a machine for converting heat, developed by burning fuel into useful work. It
can be said that heat engine is equipment which generates thermal energy and transforms it
into mechanical energy.

Classification of Heat Engine :-

1. Based on combustion of fuel:
(i) External combustion engine
(ii) Internal combustion engine.

External combustion engine

Here, the working medium, the steam, is generated in a boiler, located outside the engine and
allowed in to the cylinder to operate the piston to do mechanical work.

Internal combustion engine

In internal combustion engine, the combustion of fuel takes place inside the engine cylinder
and heat is generated within the cylinder. This heat is added to the air inside the cylinder and
thus the pressure of the air is increased tremendously. This high pressure air moves the piston
which rotates the crank shaft and thus mechanical work is done

2. Based on fuel used

1. Diesel engine
2. Petrol engine
3. Gas engine

Diesel engine – Diesel is used as fuel
Petrol engine – Petrol is used as fuel
Gas engines – propane, butane or methane gases are used

3. Based ignition of fuel

1. Spark ignition engine (Carburetor type engines)
2. Compression ignition engine ( injector type engines)

Spark ignition engine – a mixture of air and fuel is drawn in to the engine cylinder. Ignition of
fuel is done by using a spark plug. The spark plug produces a spark and ignites the air- fuel
mixture. Such combustion is called constant volume combustion (C.V.C.).
Compression ignition engine – In compression ignition engines air is compressed in to the
engine cylinder,. Due to this the temperature of the compressed air rises to 700-900 C. At this
stage diesel is sprayed in to the cylinder in fine particles. Due to a very high temperature, the
fuel gets ignited. This type of combustion is called constant pressure combustion (CP.C.)
because the pressure inside the cylinder is almost constant when combustion is taking place.

4. Based on working cycle

1. Four stroke cycle engine - When the cycle is completed in two revolutions of the
crankshaft, it is called four stroke cycle engine.

2. Two stroke cycle engine. - When the cycle is completed in one revolution of the
crankshaft, it is called two stroke cycle engine

CONSTRUCTION OF AN IC ENGINE

I.C. engine converts the reciprocating motion of piston into rotary motion of the crankshaft by
means of a connecting rod. The piston which reciprocating in the cylinder is very close fit in
the cylinder. Rings are inserted in the circumferential grooves of the piston to prevent leakage
of gases from sides of the piston. Usually a cylinder is bored in a cylinder block and a gasket,
made of copper sheet or asbestos is inserted between the cylinder and the cylinder head to
avoid ant leakage. The combustion space is provided at the top of the cylinder head where
combustion takes place. The connecting rod connects the piston and the crankshaft. The end of
the connecting rod connecting the piston is called small end. A pin called gudgeon pin or wrist
pin is provided for connecting the piston and the connecting rod at the small end. . The other
end of the connecting rod connecting the crank shaft is called big end. When piston is moved
up and down, the motion is transmitted to the crank shaft by the connecting rod and the crank
shaft makes rotary motion. The crankshaft rotates in main bearings which are fitted the
crankcase. A flywheel is provided at one end of the crankshaft for smoothing the uneven
torque produced by the engine. There is an oil sump at the bottom of the engine which
contains lubricating oil for lubricating different parts of the engine.

WORKING PRINCIPLE OF I.C. ENGINE/ FOUR STROKE CYCLE ENGINE / TWO
STROKE CYCLE ENGINE

A mixture of fuel with correct amount of air is exploded in an engine cylinder which is closed
at one end. As a result of this explosion, heat is released and this heat causes the pressure of
the burning gases to increase. This pressure forces a close fitting piston to move down the
cylinder. The movement of piston is transmitted to a crankshaft by a connecting rod so that the
crankshaft rotates and turns a flywheel connected to it. Power is taken from the rotating crank
shaft to do mechanical work. To obtain continuous rotation of the crankshaft the explosion has
to be repeated continuously. Before the explosion to take place, the used gases are expelled
from the cylinder, fresh charge of fuel and air are admitted in to the cylinder and the piston
moved back to its starting position. The sequences of events taking place in an engine is called
the working cycle of the engine. The sequence of events taking place inside the engine are as follows -

1. Admission of air or air-fuel mixture inside the engine cylinder ( suction )

2. Compression of the air or air fuel mixture inside the engine (compression)

3. Injection of fuel in compressed air for ignition of the fuel or ignition of air-fuel mixture
by an electric spark using a spark plug to produce thermal power inside the cylinder
(power )

4. Removal of all the burnt gases from the cylinder to receive fresh charge ( exhaust)

(Note: Charge means admitting fresh air in to the cylinder in the case of compression
ignition engines ( diesel engines ) or admitting a mixture of air and fuel in to the
cylinder in the case of spark ignition engines.)

COMPARISON OF DIESEL ENGINE WITH PETROL ENGINE -

DIESEL ENGINE -

1.It has got no carburetor, ignition coil and spark
plug.
2.Its compression ratio varies from 14:1 to 22:1.
3.It uses diesel oil as fuel.
4.Only air is sucked in cylinder in suction stroke.
5.It has got „fuel injection pump‟ and injector
6.Fuel is injected in combustion chamber where
burning of fuel takes places due to heat of
compression.
7.Thermal efficiency varies from 32 to 38%
8.Engine weight per horse-power is high.
Operating cost is low.
9.Compression pressure inside the cylinder varies.

PETROL ENGINE -

1.It has got carburetor, ignition coil & spark plug.
2.Its compression ratio varies from 5:1 to      8:1.
3.It uses petrol (gasoline) or power kerosine as fuel.
4.It has got no fuel injection pump and
injector, instead it has got carburetor and
ignition coil.
5.Air fuel mixture is compressed in the
combustion chamber when it is ignited by
an electric spark.
6.Thermal efficiency varies from 25 to 32%
7.Engine weight per horsepower is
comparatively low.
8.Operating cost is high.
9.Compression pressure varies from 6 to  10.