The operation of the Stirling engine is based on the expansion and contraction of a gas that can be helium, hydrogen, nitrogen or air. This gas is forced to cycle cyclically from a cold source where it contracts to a hot source where it expands. It is considered as a thermal engine ( thermodynamic engine) due to the presence of a temperature gradient between the two thermal sources.
Originally, the Stirling engine was conceived as an industrial main engine to compete with the steam engine, but in practice, for more than a century it was only used for domestic applications and for low power engines.
Currently, development is still being investigated. The fact that you only need an external heat source gives you great versatility since this fact gives you the possibility of being able to use many sources of energy for its operation. The energy source of a Stirling engine most relevant to us is solar thermal energy, although you can also use all kinds of fuels, biomass, geothermal energy and others.
Operation of a Stirling engine
A Stirling engine is a mechanical device that operates in a thermodynamically "closed" regenerative cycle, with cyclic compression and cyclical expansion of the working fluid at different temperature levels.
Like the steam engine, the Stirling engine is traditionally classified as an external combustion engine, since all heat transfers with the working gas are made through the motor wall. In contrast, in an internal combustion engine the heat input is made by the combustion of a fuel inside the body of the working fluid.
Unlike a steam engine, the Stirling engine closes a fixed amount of fluid in a permanently gaseous state such as air. In contrast, in the steam engine the working fluid undergoes a phase change from liquid to gas.
As is typical with thermal engines, the general cycle consists of compressing the cold gas, heating the gas, expanding the hot gas, and finally cooling the gas before repeating the cycle. The efficiency of the process is very restricted by the efficiency of the Carnot cycle, which depends on the temperature difference between the hot and cold tanks.
The Stirling engine is characterized by its high efficiency compared to steam engines, quiet operation, and the ease with which almost any heat source can be used. This compatibility with alternative and renewable energy sources has been increasingly important as the cost of conventional fuels rose, and also in the light of concerns, such as the peak of past oil production and climate change. This motor is currently of interest as the core of the micro-combustion units of heat and energy, that is to say of cogeneration, in which it is safer and more efficient than a steam energy.