Heat engine is a device which transforms the chemical energy of a fuel Into thermal energy; utilize this thermal energy to perform useful work. Thus, thermal energy is converted to mechanical energy. Heat engines can be broadly classified into two categories:
- Internal Combustion Engines (IC Engines)
- External Combustion Engines (EC Engines)
In external combustion engines the combustion takes place external to the cylinder, e.g., steam engines.
In internal combustion engines the combustion takes place inside the cylinder, e.g., petrol, diesel, gas engines.
The main advantages of internal combustion engines over external combustion engines are greater mechanical simplicity, lower ratio of weight. A bulk output due to absence of auxiliary apparatus like boiler and condenser. The cost is lower, higher overall efficiency and lesser requirement of water for dissipation of energy through cooling system.