The air engine is an emission-free piston engine that uses compressed air as a source of energy. The expansion of compressed air may be used to drive the pistons in a modified piston engine. Efficiency of operation is gained through the use of environmental heat at normal temperature to warm the otherwise cold expanded air from the storage tank. This non-adiabatic expansion has the potential to greatly increase the efficiency of the machine. The only exhaust is cold air (−15 °C), which could also be used to air condition the car. The source for air is a pressurized carbon-fiber tank. Air is delivered to the engine via a rather conventional injection system. Unique crank design within the engine increases the time during which the air charge is warmed from ambient sources and a two stage process allows improved heat transfer rates
The Stirling engine is a heat engine that is vastly different from an internal combustion engine. Stirling engines have two pistons that create a 90-degree phase angle and two different temperature spaces. The working gas in the engine is perfectly sealed, and doesn't go in and out to the atmosphere. The Stirling engine uses a Stirling cycle, which is unlike the cycles used in normal internal combustion engines
- The gas used inside Stirling engine never leaves the engine. There are no exhaust valves that vent high-pressure gases as in petrol or diesel engine, and there are no explosions taking place.
- The Stirling cycle uses external heat source, which could be anything from gasoline to solar energy to heat produced by decaying plants. No combustion takes place inside cylinder of the engine.