INTRODUCTION

An engine may be defined as a device which converts one form of energy into mechanical energy. Mechanical energy can be further easily converted into electrical energy which is easier to transport and control. Heat engine is a cyclic device which transforms heat energy into mechanical energy.

Heat engines are classified into the following:

1. External combustion engines
2. Internal combustion engines

In an external combustion engine, the fuel is burned outside the engine and the generated heat is supplied to the working fluid of the engine for power generation. Steam engine is an example of an external combustion engine in which fuel is burned in the boiler to generate steam, which is used in the engine for power generation. The working fluid is not mixed with fuel, and the same working fluid (water in the form of steam) is repeatedly used in the system.

In an internal combustion (IC) engine, the fuel is mixed with air and burned inside the engine to generate power. In this case, the same working fluid (air-fuel mixture) cannot be used again in the cycle. Some examples of internal combustion engine are spark ignition (SI) engine, compression ignition (CI) engine, etc.

IC engines offer the following advantages over external combustion engines:

1. Greater mechanical simplicity
2. Lower weight to output ratio
3. Higher overall thermal efficiency
4. Less water requirement
5. Easy and quick starting