A gas expansion engine, a driving machine (even compressed air) is operated using compressed ( pressed together ) gas.
The work flow of a gas expansion engine equivalent to a steam engine, both of which belong to the piston engines. The inlet valve opens and allows the gas under high pressure in the expansion space (cylinder). According to closing of the intake valve, the gas expands to the expansion end point. The gas absorbs heat energy from the environment. The gas flows out through the outlet valve at the required residual pressure. The motor can be run as a single-acting piston engine as well as double-acting machine. In the low power range but are also rotary piston and the like. for execution.
The statement by the gas expansion engine mechanical work comes in adiabatic relaxation case of the integral enthalpy stored in the gas. In isothermal relaxation the mechanical work output increases by the recorded exergy.
A further possibility to transform the inherent pressure in gas enthalpy into rotation, providing the vane motor.
From the end of the 19th century gas expansion engines were built, which were operated with carbon dioxide from pressurized cylinders. With these so-called " carbonic engines " turntable ladders were moved, for example, and Otto Lilienthal experimented with them as a drive for its aircraft.
Gas expansion motors can be used as a pressure regulator. The range of applications for large gas expansion motors ( > 5 kW) is the energy recovery during gas withdrawal from gas pipelines.
The most common application is the expansion of small gas engines that are powered by compressed air and power hand tools. Relatively frequently, the use of free piston machines, which operate as a pump.
In principle, can the gas expansion motor vehicle use as a power source, but in the past, to be carried in pressure tanks entropy was so small and the overall efficiency is so low that the use was not economical. Only for torpedoes were long air motors as drive in use.
From the 1990s until about the year 2002, there were projects and announcements that there will be a production-ready vehicle with air drive, the Aircar or compressed air car. These announcements have now been replaced by a Luxembourg-based French company that announces to want to produce the so-called OneCat from 2009. The announcement was not implemented.