Air Engine

In production
http://www.youtube.com/watch?v=f4w6aJMNXSk SA obtained a production license. The engine has 20 patents to HackPatents via a fronting company in South-Africa.
 * http://zeropollutionmotors.us/

https://en.wikipedia.org/wiki/Motor_Development_International, http://www.mdi.lu/

http://en.wikipedia.org/wiki/Compressed_air_energy_storage

http://en.wikipedia.org/wiki/Pneumatic_motor

compressed air battery
http://en.wikipedia.org/wiki/Compressed_air_battery

https://en.wikipedia.org/wiki/Hydraulic_accumulator

http://kair-energy.com/index.php from   https://en.wikipedia.org/wiki/Compressed_air_car#cite_note-39. This is probably a better solution than stirling engines. K°Air’s Pressure Power System: K°Air has developed its multi-patent pending Pressure Power System that is the first and only to harness the Ambient Temperature of the existing surroundings, ranging from only 0°C to 35°C, to produce electricity, as opposed to the 300°C to 650°C required by steam turbines. This Ambient Temperature is sourced from the temperature outdoors; the room temperature of a building, office or home; or the temperature inside a manufacturing or industrial facility, where the temperature is warmer because of the heat generated from operations such as a foundry, manufacturing, mining, pulp & paper, textiles, commercial kitchens & bakeries, or dry cleaning. The K°Air Pressure Power System can achieve an average capacity utilization ranging from 75% to 95% from the Ambient Temperature alone, which can be increased if and when necessary from other sources of green energy including solar, wind or water mills, geothermal, biomass and commercial or industrial heat recovery sources. The K°Air Pressure Power System represents a major improvement of steam turbine generator systems, which currently produce more than 80% of the world's supply of electricity.