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Petrol Engine | Difference Between Petrol Engine And Diesel Engine

August 6, 2022
written by Adeel Abbas

Petrol engines are the types of heat engines in which internal combustion has spark ignition. it runs on relatively volatile fuels such as petrol. The Basic principle of the engine is the second law of thermodynamics.

Petrol Engine

A gasoline engine is an internal combustion engine with spark-ignition, designed to run on petrol.

Working Principle of petrol engine:

 All the petrol engines are based on the principle of a Carnot cycle.

Construction of Petrol engine

it consists of:

  • Spark plug
  • Piston
  • Crankshaft
  • Valves
image showing the petrol engine

Working on petrol Engine

A typical four-stroke engine undergoes four cycles. These are:

Inlet Stroke

In this stroke, the piston moves outward and the petrol air mixture from the carburetor is drawn into the cylinder from the inlet valve.

Compression Stroke

In this stroke, the piston is moved inward and the mixture is compressed adiabatically.

Power Stroke

In this stroke, a spark from the spark plug burns the petrol air mixture due to which the temperature and pressure are increased. As a result, the gases expand adiabatically and move the piston outward. The piston moves the crankshaft, which in turn moves the flywheels.

Exhaust Stroke:

In this stroke, the outlet valve opens and the gases are expelled out. The piston then again moves inwards. The cycle then begins again. Motorbikes have a one-cylinder engine but cars have four-cylinder engines on the same crankshaft.

 The efficiency of Petrol Engine

 The efficiency of petrol engines is only 25% to 30% due to friction and heat losses.

What is a diesel engine?

No spark plug is needed in a diesel engine. Diesel is sprayed into the cylinder under maximum compression, so the temperature rises to a maximum value. As a result, the fuel mixture gets ignited and produces gases of large volume. Due to this, the piston moves upward.

The efficiency of Diesel Engine

 The efficiency of a diesel engine is 35% to 40%. The diesel engine is more efficient than a petrol engine

Difference between Petrol and Diesel Engine

Diesel EnginePetrol Engine
Diesel engines work on the Diesel cyclePetrol Works on the basis of the Otto cycle
In a diesel engine ignition start with the help of hot, compressed air.In a petrol engine Fuel is ignited with help of an electric spark
inside the cylinder, the fuel is mixed with airAir and fuel are mixed in a carburetor
The diesel engine has a High compression ratioThe engine has a low compression ratio as compared to the diesel engine
The power production of diesel engines is highThe power production of a petrol engine is low relatively
diesel engines work with fuels that have low volatilitiesHighly volatile fuels are used in this engine
These engines are used in heavy vehicles such as bus trucks etc.These engines are used in light vehicles such as cars.
The fuel consumption of diesel engines is lowThe fuel consumption is high
Its maintenance cost is highIts maintenance cost is low
Its initial cost is highIts initial cost is low comparatively