The Stirling engine is the engine, which uses a fixed amount of gas sealed inside a cylinder. The expansion and contraction of the gas, using heat from external source, creates the useful work. The main advantage of this engine is its capability to use any type of fuel and the emission of no exhaust gases.

Due to this pollution free and use of any type of fuel characteristics the Stirling engine shows a greater potential over any other type of engine existing today. To consolidate this claim an effort has been made to develop a working model of Stirling engine.

All of us including the lamest of laymen would have at one time or another experienced problems with our vehicles engine and most of the time after moaning and cursing finally in line with the universe and accepting our doom we would have coughed up the cash for repairs and parts and insistently taken old parts home, disregarding the fact that no descent human would have wanted them and during this exercise in existence it is doubtful that anybody would have chance to miss seeing a piston or two, this ubiquitous creatures that scurry up and down in an enclosed cylindrical space, getting their crowns slammed regularly and unceremoniously…eventually to be thrown aside and replaced by a marginally wider chap. Doubtful that any of us would be able to imagine modern travel without an internal combustion cycle. Hell if we ask our mechanic if he has ever seen a vehicle without any exhaust then he is probably going to refer to you to the nearest shrink.

So an engine without any exhaust gas is a mirage or it can be a reality? The answer for this is definitely yes. We can have an engine without any exhaust gas and that is what a Stirling engine is.

The Stirling engine is a heat engine that is vastly different from an internal combustion engine. Stirling engines have two pistons that create a 90-degree phase angle and two different temperature spaces. The working gas in the engine is perfectly sealed, and doesn't go in and out to the atmosphere. The Stirling engine uses a Stirling cycle, which is unlike the cycles used in normal internal combustion engines.

The gas used inside Stirling engine never leaves the engine. There are no exhaust valves that vent high-pressure gases as in petrol or diesel engine, and there are no explosions taking place.

The Stirling cycle uses external heat source, which could be anything from gasoline to solar energy to heat produced by decaying plants. No combustion takes place inside cylinder of the engine.

Stirling engines can be classified as:

• Two pistons type Stirling engine

• Displacer type Stirling engine.