A heat engine typically uses energy provided in the form of heat to do workand then exhausts the heat which cannot be used to do work. Thermodynamics is the study of the relationships between heat and work. The first law and second law of thermodynamics constrain the operation of a heat engine. The first law is the application of conservation of energy to the system, and the second sets limits on the possible efficiency of the machine and determines the direction of energy flow.
The efficiency of a heat engine is defined as the work out divided by the energy in.
Efficiency = (Work out) / (Energy in)
= (Work out) / (Heat in) by conservation of energy this is also Efficiency
= (Heat in - Heat out) / (Energy in)
= 1 - (Heat out) / (Heat in)
Types of Heat Engines
The two main types of heat engines
Internal Combustion Engines
The Internal combustion is a process in which the combustion of a fuel occurs within the system. Internal combustion engines are type of Heat engine in which the fuel is burnt inside the engine or where fuel combustion takes place inside the engine.
External Combustion Engines
External combustion engines are type of heat engines in which the fuel is burnt outside the engine or where fuel combustion takes place outside the engine. First practical steam external combustion engine was developed by Thomas Newcomen in 1712. It was used to pump the water out from coal mines.