Engine definition and Types

Define “Engine”:

An engine is a device which transforms one form of energy into another form. However, while transforming energy from one form to another, the efficiency of conversion plays a major role. Normally, most of the engines convert thermal energy into mechanical energy and hence called “heat engine”.

Define “Heat engine”:

                A heat engine is a device which transforms the chemical energy of a fuel into thermal energy and utilizes this thermal energy to perform useful work. Thus, thermal energy is converted into mechanical energy in a heat engine.

Heat engines are broadly classified into two.

i)                    Internal Combustion Engines (IC Engine)

ii)                   External Combustion Engines (EC Engines)

IC or EC engines are of two types.

i)                    Rotary Engines

ii)                   Reciprocating Engines

Of the various types of engines, most widely used are the reciprocating internal combustion engine, gas turbine and the steam turbine.  Reciprocating IC engines are the most advantageous than the steam engines due to absence of heat exchanger resulting in mechanical simplicity and improved efficiency of IC engines. Another advantage is that its average temperature is much below the maximum temperature of the working fluid in the cycle. This is because, the high temperature of the working fluid exist only for a short fraction of time. So, very high working fluid temperatures can be employed for obtaining higher thermal efficiency.

It is possible to develop reciprocating IC engines of very smaller power with reasonable thermal efficiency. But, the main disadvantage of this type of engine is the vibration caused due to reciprocation. Reciprocating IC engines are found suitable for use in automobiles, motorcycle, power boats, etc.