What is Stirling Engine?

Outline of Stirling Engine

Speaking of an engine, you will remember a gasoline engine immediately.　In a gasoline engine, gasoline and air mixture is delivered into a cylinder, and it is burnt instantaneously by igniting in the cylinder. The instantaneous　combustion drives piston to produce engine power.

In this case, however,it is rather difficult to realize a perfect combustion since the ombustion is carried out almost forcibly in a small room of cylinder, resulting in emission of pollutant such as carbon monoxide and nitrogen oxides.

Operation principle of Stirling Engine is rather different from one of gasoline　engine. This engine also has cylinder and piston. In the cylinder, air, hydrogen or helium gas is sealed. When the cylinder is heated from outside, the gas expands as the temperature rises, and drives a piston. Of course, only continuous heating of the cylinder cannot produce a continuous engine　power because the gas keeps the state of expansion.

So this engine realizes　continuous reciprocating motion by incorporating a gas-cooling system ( displacer )　in the cylinder. A series of this operation is referred to “ the Stirling Cycle “.

Detailed explanation follows:

Detailed explanation of operation principle of Stirling Engine.

Compression – Heating		Power piston(green) moves to the right end (bottom) and cooled gas in the left room moves into the right room passing through a regenerator (orange). In this process, a displacer (yellow) started to move to the left so that the gas can enter to the right room easily. When the gas passes through a gas regenerator, the gas temperature rises getting a part of heat stored in the regenerator. The gas entered in the right room rises its temperature rapidly and starts to expand.
Heating – Expansion		As the gas expands, the expanded gas in the right room moves to the　left room passing through regenerator and increases the pressure　inside the left room. The heated and expanded gas leaves a part of its inherent heat on the ｒegenerator when passes through the regenerator. (Under the condition, gas pressure of both, right and left, rooms rises. ) Due to this rising gas pressure, power position is pressed to the left and rotate a wheel through a crank mechanism(=drive power is realized). Displacer moves to the left, but no effect on the pressure for pushing　power piston.
Expansion – Cooling		Due to the expanded gas pressure, power cylinder moves fully to the left (top dead　point) and displacer starts to move to the right and the volume of the left room　becomes largest. The left room is cooled by cold water circulating on the outer surface of the room. The gas in the room becomes cool and starts to contract.
Cooling – Compression		Displacer moves to the right end and fully occupies the right room. Gas is not heated accordingly. Power piston starts moving to the right by means of energy the flywheel has, and presses the cooled gas to the right room through regenerator. With the above, the Stirling Engine Cycle ends.
Continuous operation		For your easier understanding, one operation process of the cycle is shown in a second.

For an internal combustion engine, Stirling Engine is often called an external combustion engine since it gets energy(heat source) outside the cylinder. There are many types of the heat source. A typical type you can imagine is a cooking stove. When you cook, you put wood on a fire to heat pot or pan. Such　cooking pot just corresponds to “a heater head” of Stirling Engine. Not only wooden fuel but any combustible material can be a fuel for Stirling Engine. This means that you can get electricity and driving power without using fossil fuel such as oil etc. Furthermore, you can get even heat for space heating and hot water by utilizing waste heat from this engine. The fuel for Stirling Engine we expect most is biomass. More detailed explanation is given for you in another pages.