"Air!"

In the United States, the average cost of a gallon of gasoline is consistently above $3.00 per gallon. Therefore, there is an increasing interest in developing alternative energy solutions more now than ever. Currently one popular solution is the hybrid electric vehicle, which is now produced by every major automotive manufacturer. Although these vehicles reduce emissions and fuel consumption, they still rely on the use of petroleum-based fuels to achieve their higher fuel economy. Looking into the future we can ask, "What is the next step in this evolution, hydrogen, CNG, propane?" Nobody really knows, but there are still engineers and inventors looking to a different source of energy to power our cars: air.

That's right, air! The same substance that we all breathe every day, but how does this technology work? The principle behind this technology is very similar to that of a conventional internal combustion engine. Just like in your car there is an expansion stroke and exhaust stroke, but unlike your car there is no need for an intake stroke or compression stroke. This is because the air is stored on board the vehicle under high pressure, up to 300 bar.

The compressed air is released from the storage tank and is sent to the engine's injectors. When the piston in the cylinder reaches top dead center, the air is released into the combustion chamber where it expands and forces down the piston in the cylinder. As the piston reaches bottom dead center, the exhaust valves open and allow the air to escape out of the exhaust pipe to the atmosphere.

The design of the Air Car's 75 hp engine is quite unique. Credit: www.theaircar.com

The interesting question is where does the compressed air come from? This would vary depending on the vehicle design. America-based company Zero Pollution Motors is proposing a small onboard gasoline engine that will run an onboard compressor. It claims that through the process the gasoline engine will only run when the vehicle is operating above 35 mph, and the pollutants for this small engine are about half of the CO2 that is produced by a 2007 Toyota Prius. Another solution from a company in France, Motor Development International, is to offer a plug-in onboard compressor that one would plug into a household wall outlet. The plug-in compressor will take approximately one hour to fill the tank.

The U.S. version of the Air Car is set to go on sale late in 2009. Credit: http://zeropollutionmotors.us

All of this is good news, but the important part is whether it is still going to perform like a normal vehicle. From reviewing these various companies' information, they are claiming top speed in the range of 100 mph. Also, depending on the compressor option, gasoline or electric, the range is estimated to be around 106 gasoline-equivalent mpg by Zero Pollution Motors. With an eight gallon tank, the vehicle is expected to achieve more than 800 mpg.