Are pneumatic cars a lot of hot air?

Tata Motors of India has announced it will build a car that runs on compressed air. A pneumatic car.

Before you dismiss Tata as airheads or escapees from a rubber room, it would be fair to point out they bought the Jaguar/Land Rover group from Ford – for cash.

Tata’s parent company owns about 60 companies that operate on a worldwide basis. The one we are most familiar with is Tetley Tea.

The other reason that you can’t label these guys as funny farm material is that MDI of Luxembourg has been working on such a car since 1991.

Guy Negre, MDI founder, worked in the aerospace industry before moving to the Life Formula One team, a flash in the pan for the 1990 Grand Prix season.

A car that runs on compressed air isn’t as far out as it seems. Negre claims that with average city use, his car will be able to go about 300 kilometres on a charge of air. The car will be devoid of all luxuries and make an impressive use of lightweight body materials and electronics. There are test models operating on the road, undergoing fine tuning for consumer use. Projected cost in India is less than $10,000.

To suggest there are drawbacks to such a car is an understatement. One limiting factor is ambient air temperature. Pneumatic cars work best in climates with fairly constant and high air temperatures. As air cools, it loses energy, which shows up as reduced pressure.

A good example is a balloon filled at room temperature then put in the freezer for an hour. The balloon appears to be nearly empty until warmed up again.

That pretty much excludes an air car for Canada, but makes it workable in India.

Even in India, Tata admits the fueling infrastructure has yet to be built. Storage pressure of the air is about 4,500 psi, so it requires specialized handling. When air is compressed, it creates heat. Heat expands the air. This means that the temperature of the tank has to be controlled or the full 4,500 psi will not go in when the tank comes back to ambient temperature.

The reverse is also true. When air expands, it cools. If there is any moisture present, the moisture freezes and blocks the line. Just drain your air compressor after use on a humid day to see what I mean.

On the positive side, an air car does not need cooling, coolant, a water pump or hoses. The engine does not need to be made of heavy cast iron with massive cooling chambers. It will not need four, six or eight cylinders. Two will do the job for this city car.

While the carbon fibre fuel tank needs shielding, it is not corrosive or explosive. The carbon fibre may crack if damaged, but won’t produce shrapnel.

The exhaust system does not need a catalyst or special cleaning because air coming in is the same as air going out. Without contaminants, oil changes can be done every 50,000 km. The air motor requires about a litre and half of vegetable oil.

A few other facts that make an air car attractive are fuel costs. With fuel around a $1 per litre and our high electrical costs, it will go about 200 km and cost about $2 to fill up.

This is a bit deceiving at the moment because commercial filling isn’t readily available. The car does have a small onboard compressor that takes up to four hours to fill the tank if needed.

The air car becomes practical in the large cities because 80 percent of all driving in India is done in the city and the climate varies from hot to real hot.

In addition, anything that can be done to improve air quality by removing carbon emissions in these cities is an improvement.

The Tata air car is not a one-size-fits-all solution to air pollution, but for a large part of the world’s population, it is a practical solution. Here in Canada, it would be a toy with limited use, at least for the present.

Charles Renny is an automotive columnist and a member of the Automobile Journalists Association of Canada.

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