The principle of operation of this engine is the work done by the expansion and contraction of a gas, typically helium, hydrogen, nitrogen, or simply air. It must follow a cooling cycle in a cold focus shrinks, and the heat in a light bulb hot, it expands. That is, it is necessary the presence of a temperature difference between the two foci and is, therefore, of a heat engine.
The work cycle consists of 2 isochores (heating and cooling at constant volume) and 2-isotherms (compression and expansion at constant temperature). The hot air engine Stirling uses a heat source fixed to heat air in your cylinder. It can be considered as an external combustion engine for gear motors as it is governed by an adiabatic process, since it does not require burning fuel in its interior and to operate does not transfer heat to the environment.
Hot and cold air
Their movement is due to the differences of air pressure between the portion more hot and cold. The central mechanism of a Stirling consists of two pistons/cylinders, one to dissipate heat and move warm air toward the cold section, and vice versa. In practice, this cylinder functions as a heat exchanger called regenerator, while the other piston delivers the force to apply torque or motor torque to the crankshaft.
Using a proper design of this motor, it is possible to get two pulses of power for each turn of the crankshaft which makes this engine the most efficient that is known; however, it suffers from a problem that it determines not to be of the impeller ideal for large number of machines, your inability to put it into place instantly. In front of the engines of external combustion has the advantage of minimising the emissions of greenhouse gases, as well as the ability to accept sources of heat without combustion.
Today there is a variety of devices that use this principle, even some with acoustic base, however, it has no application in the automotive industry for several reasons:
- Although its performance is higher, its power is inferior to an equal weight and the optimum performance is only reached at low speeds. There is an additional element to the engine, called a regenerator, which, although not indispensable, allows to achieve higher yields. The regenerator is a porous medium with thermal conductivity despicable that contains a fluid. Acts as an internal heat exchanger and absorbs and transfers heat in the evolutions to a constant volume cycle.
The regenerator divides the engine into two zones, one hot and one cold, and the fluid moves from the hot zone to the cold during the various work cycles.
- The cycle theoretical Stirling is unattainable in practice, and the cycle Stirling royal has a performance intrinsically lower than that of Otto cycle.
- The performance of the cycle is sensitive to the outside temperature, so that its efficiency is greater in cold climates like winter in the nordic countries, while he would have less interest in climates such as those of the equatorial countries.