Heat engine

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

  • 1. Internal Combustion Engines
  • 2. External combustion 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.

    Heat Engine Examples

  • Phase Change Engines: In these engines the mechanical work is done by the phase change of the working fluid which can be a gas or a liquid. In this engine a gas changes to a liquid and vice versa to generate a mechanical work.
  • Rankine Engines: These are classical steam engines.
  • Regenerative Engines: They are also a kind of steam engine but more efficient than the Rankine engines.
  • Gas Engines: In these engines only gases are used as working fluid and there is no phase change.
  • Carnot Heat Engine: A theoretical engine.
  • Liquid Engines: In these engines the working fluid are always liquid.