Page 51 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

MODULE 2 : Engine System

LESSON 08 - 10: Explanation of Principle of All types of SI

and CI Engines with respect to pressure,
volume and temperature

Objectives

At the end of this lesson you shall be able to
• explain principles of SI & CI engines
• understand and explain PV diagram.

Petrol Engine - Petrol fuel based engine is a type of internal combustion engine which is made up of gasoline
and Also known as spark ignition engine. These engines generally occupy less space and due to low torque, there
is no need to strengthen the parts used in it. These engines are mostly used in cars, scooters, motorcycles etc.
Principle of petrol Engine -The petrol engine was invented by Nikolaos Otto; hence it is also called Otto cycle
engine. Its design is like a large stationary single cylinder internal combustion engine. Often these engines are
also known as low revolutions per minute (RPM) machines. These engines produce combustion in every second
stroke due to the Otto cycle; Like car etc. Otto cycle is also called constant volume cycle, because the exchange
of heat in it depends on constant volume.
Working method of petrol Engine -In the mechanics of petrol engines, when the mixture of petrol and air
enters the cylinder, power is generated as a result of combustion.

In the suction stroke (1-2) of a petrol engine, the piston is at T.D.C. (TDC) to B.D. C. (BDC) and the suction
process starts at a pressure lower than atmospheric pressure. After this, during the compression stroke (2-3)
when the piston B. When the cylinder goes from D.C. to T.D.C., the mixture of petrol and air present in the cylinder
is compressed.
In the heat addition stroke (3-4), the fuel mixture is ignited by sparking at a constant volume by the spark plug,
then during the power expansion stroke (4-5), the temperature and pressure are Increased due to the expansion
of the gas generated in the cylinder. Both are reduced
Types of petrol engine
1 Two stroke engine

2 Four stroke engine

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