Compressed air has long been used to store energy and drive machines like pneumatic drills, and air cylinders. Even in large transport vehicles like trucks and buses, air assisted brakes are being used. The use of compressed air as the primary power source in a car has been the subject of research and engineering, in the quest for an alternative to the pollution caused by internal combustion engines. The first air powered cars were made as far back as 1920.
The use of compressed air technology (CAT) is, in itself, non-polluting. There are, however, emissions associated with compressing the air to the required pressure, which needs a powered engine. CAT technology application to cars has been back in the news with reports of Tata Motors launching an air car. The technology still looks distant but that has not deterred inventors from working on it.
Trends
1. Compressed air car by Derek McLeish
Derek McLeish of Lompoc, California has made a car running on compressed air, stored in scuba diving tanks. He modified an engine used on the Honda RC51 998 cc Superbike. He blocked off one of the cylinders of the engine and used the spark plug hole on the other cylinder to feed the compressed air. The compressed air drives the piston down as the power stroke. At the end of the power stroke, the compressed air is released through the exhaust valves and the exhaust is only air. The pistons were connected to the wheels through the Honda bike’s six-speed transmission.This modified engine was mounted on a tubular frame and a body, that looked like a curious crossbreed of a motorbike with a racing car.
Derek McLeish used a bank of three scuba tanks to store compressed air at 3500 psi. He throttled it to 250 psi at the engine inlet with a self-designed throttle valve, linked to the accelerator pedal. The three tanks were sufficient for the test run over the 2 mile Bonneville Flats race, where he achieved an average speed of 46.723 mph and a top speed of 54.058 mph. Derek McLeish says that he is confident of achieving even 300 mph with compressed air.
Several issues still remain before this concept can translate into a usable idea. The three tanks for the two mile race, translates to several hundred tanks to achieve an acceptable range of 100 to 200 miles. That many tanks would make the car too large and too heavy.
2. Teenager invents air-powered perpetual car engine
Maruf Karimov a teenager from Samarkand in Uzbekistan has modified a friend’s car to run it with compressed air, stored in a tank. He claims that as the car runs, it will take in air and store it in the tank at pressure, resulting in a perpetual motion machine.
Perpetual motion machines are, of course, not possible under the known laws of physics but the idea is not being dismissed as crank. The concept of compressed air being regenerated while the car is in motion, is intriguing. It is akin to batteries of electric vehicles using regenerative charging and even a part regeneration of compressed air would be an advance from the present understanding of the technology.
3. Tata/MDI One CAT
Tata Motors are reported to have signed an agreement with the Motor Development Institute (MDI) of Luxembourg to produce an air powered car in India. The car is said to have been developed by Guy Negre, the CEO of MDI, who is said to be a previous Formula 1 car engineer. The reports claimed that versions of the car were being evaluated by the airline KLM, as a passenger transport pod at airports.
The car would use air powered engines designed by MDI. The compressed air would be stored at 300 psi in a carbon fiber tank lined with thermoplastic. The body would be of fiberglass, mounted on a tubular steel frame. The frame components would be joined by epoxy glue instead of welding, based on technology already being applied in the aircraft industry. The car would incorporate advanced electronic controllers.
The top speed was said to be 105 kmph with a range of 200 – 300 km per tank filling. The compressed air could be filled at existing petrol pumps in a few minutes. The cost of compressed air was estimated to be one-tenth the cost of petrol per km. The air compression at the filling stations could be at off-peak hours and could later use renewable energy sources such as wind or solar. As an alternative to kerb-side air filling, the car could be connected to an electric compressor overnight to recharge the tank in 3 to 4 hours.
To top all this, the price of the car was reported to be around $ 8200, the same as the price of entry-level gasoline cars.
There are also reports of a hybrid version with a gasoline engine added to the air engine. For city driving, the air engine would be used. Where longer highway driving is required, the gasoline engine would kick-in and in parallel to driving the car, would recharge the compressed air tank.
Many skeptics have dismissed the claim of imminent launch of a commercial air powered car as a hoax and an engineering impossibility. The reports on the Derek McLeigh car in terms of number of tanks and range seem to support the hoax theory.Tata Motors have not made any official response to these reports. The first reported date of launch was August 2011.
The benefits
The major benefit of an air powered car is, clearly, its non-polluting feature. Air is a vast renewable resource and compressing air to the needed pressure is a well established, though energy intensive process.
The lowdown
The engineering impossibility that the skeptics talk of, is the fact that compressed air even at 4500 psi pressure can deliver only 50 watthours of energy per liter volume. This is miniscule in comparison with gasoline that delivers a usable 1694 watthours per liter (though the fuel itself contains 9411 watthours per liter).
In addition, air compression is an energy intensive process and even if off-peak utility power is used, it is likely to be from fossil fuel burning power stations.
The impact
Air power is certainly one of the alternative technologies that need to be evaluated as humankind looks for alternatives to the use of petroleum fuels. The first possible applications of air powered vehicles are likely to be in limited range vehicles like the passenger pods. The deployment of vehicles on such applications could help advance the technology to a point where air power could get considered as the power source for cars.
