stirling engine

A Stirling engine is a heat engine operating by cyclic compression and expansion of air or other gas, the working fluid, at different temperature levels such that there is a net conversion of heat energy to mechanical work.

 Invented by Robert Stirling in 1816 in Scotland, the Stirling, engine uses simple gases and natural heat sources, such as sunlight, to regeneratively power the pistons of an engine. There are usually two pistons, at 90° to each other, that can be connected to a crankshaft to move a vehicle or a generator to make electricity. Stirling engines are used because they require no replenished source of fuel, run silently, and eject no emissions.

                          Stirling Engine

Functional description

The engine is so designed that the working gas is generally compressed in the colder portion of the engine and expanded in the hotter portion resulting in a net conversion of heat into work.
 "An internal Regenerative heat exchanger increases the Stirling engine's thermal efficiency compared to simpler hot air engines lacking this feature".

Regenerator

In a Stirling engine, the regenerator is an internal heat exchanger and temporary heat store placed between the hot and cold spaces such that the working fluid passes through it first in one direction and then the other.

 The primary effect of regeneration in a Stirling engine is to increase the thermal efficiency by 'recycling' internal heat which would otherwise pass through the engine irreversibly. As a secondary effect, increased thermal efficiency yields a higher power output from a given set of hot and cold end heat exchangers.