The air engine is an emission-free piston engine using compressed air as fuel that was invented by Guy Nègre, a French engineer.

It uses the expansion of compressed air 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 gas is cold air (−15 ºC), which is also used for air conditioning in a car. The source for air is a pressurized carbon-fiber tank holding air at 3,000 lbf/in² (20 MPa). 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.

This engine is used to power an urban car with room for five passengers and a projected range of about 100 to 200 miles (160 to 320 km), depending on traffic conditions. The main advantages are: no roadside emissions, low cost technology, engine uses food oil for lubrication (just about 1 liter, changes only every 30,000 miles (50,000 km)) and integrated air conditioning. Range could be quickly tripled, since there are already carbon fiber tanks which have passed safety standards holding gas at 10,000 lbf/in² (70 MPa).

The tanks may be refilled in about three minutes at a service station, or in a few hours at home plugging the car into the electric grid via an on-board compressor. The cost of refilling is projected to be about US$3.

However, the air engine and refueling system, considered as a system, are not pollution free except in special cases, as the electric power generation would have its own environmental costs. One of the special cases is where an operatator of such a vehicle installs photovolatic or wind drive electric power generation, quite cost effective if the operator can use time-of-use net metering, where power produced is credited at a higher rate than its use to recharge a vehicle using off-peak rates.

Also, performance and range features noted above are based on theoretical projections based upon experiment, prototype performance, engineering analysis and proposed developments. So far (early July 2004), no information has been forthcoming from the developers or other interested parties as to an actual vehicle that can perform as stated. If successful, the project will definitely advance the state of the art in zero pollution developments, principally because it does not have the limited battery life and consequent periodic battery replacement costs of an electric vehicle. Furthermore, the ability to quickly replenish the energy store in a time comparable to filling the tank of a liquid fuel vechicle will be far superior to anything that a battery electric vehicle can deliver and will enable an operator to make long trips within the availability of fast charging stations.

See also

• City car
• Electric vehicle
• Zero-emissions vehicle

External links

• There are pictures and complete information at: www.theaircar.com
• How Stuff Works