Engine & Working Principles

A heat engine is a machine, which converts heat energy into mechanical energy. The combustion of fuel such as coal, petrol, diesel generates heat. This heat is supplied to a working substance at high temperature. By the expansion of this substance in suitable machines, heat energy is converted into useful work. Heat engines can be further divided into two types:

(i) External combustion and

(ii) Internal combustion.

In a steam engine the combustion of fuel takes place outside the engine and the steam thus formed is used to run the engine. Thus, it is known as external combustion engine. In the case of internal combustion engine, the combustion of fuel takes place inside the engine cylinder itself.

The IC engine can be further classified as:

(i) stationary or mobile,

(ii) horizontal or vertical and

(iii) low, medium or high speed.

The two distinct types of IC engines used for either mobile or stationary operations are:

(i) diesel and

(ii) carburettor.

Chart 1. Types of Heat Engines

Spark Ignition (Carburettor Type) IC Engine

In this engine liquid fuel is atomised, vaporized and mixed with air in correct proportion before being taken to the engine cylinder through the intake manifolds. The ignition of the mixture is caused by an electric spark and is known as spark ignition.

Compression Ignition (Diesel Type) IC Engine In this only the liquid fuel is injected in the cylinder under high pressure.