A heat engine is a device which transforms the chemical energy of a fuel into thermal energy and uses this energy to produce mechanical work. The majority of world’s power is still produced directly or indirectly from heat provided by burning fuel such as coal and oil. The energy conversion follows a pattern outlined below.
Chemical energy in fuel⇒Heat energy⇒Mechanical energy + Wasted heat
Heat engines are classified into two types-
(a) External combustion engine
(b) Internal combustion engine.