Compressed Air Car Has Backers, Detractors and a U.S. Production Date

By Robert E.Calem, Contributor

The best minds in the auto industry are busy developing all sorts of new "green" vehicles powered by high-tech batteries, hydrogen fuel cells

and even advanced internal combustion engines sipping good old-fashioned gasoline or diesel fuels. Could they all be misguided?

Guy Negre and Shiva Vencat believe they are.

Negre is the CEO and founder of Motor Development International (MDI), a tiny company based in Luxembourg that has developed a family of automobiles powered by compressed air. Vencat is the company's exclusive representative in the U.S.

The two claim that a compressed-air car is a better alternative than any of those other technologies. They also maintain that MDI's compressed air technology is already viable for mass production, and they note that India's Tata is licensed to use it in vehicles that would be marketed in that country.

Of course, credible naysayers abound, including experts in automotive powertrain engineering who point to the technology's inefficiencies and warn that a car with a compressed air engine would be impractical for the long-distance highway driving that is common in the U.S. and other developed nations.

Nevertheless, Negre and Vencat are undaunted by the criticism, which they insist is unfounded and unsubstantiated. The critics have not driven MDI's compressed-air car, and would be converted to believers if they did, the two say. 

In a recent meeting with Green Car Advisor in New York, the Negre and Vencat briefed us on the company's compressed air technology and its product plans. Negre spoke entirely in French while Vencat translated.

MDI's "compressed air vehicles" or "air cars" will achieve twice the mileage of the Toyota Prius, emit zero or near-zero pollutants and cost practically nothing to operate, they say.

They're promising that MDI's first commercially available models will begin rolling off assembly lines in France as soon as the first half of next year, with sales in the U.S. to follow in late 2010.

To gain public attention and show off their technology, they've entered one of their air cars in the Progressive Insurance Automotive X PRIZE , a contest for commercially viable vehicles that go farther than 100 miles on a gallon or gallon-equivalent of fuel.

How It Works

In its most basic "mono-energy" form, the MDI compressed-air car's engine uses only compressed air stored in a reinforced carbon-fiber tank that contains 90 cubic meters (3,178 cubic feet) under 4,500 psi (pounds per square inch) of pressure. That's the equivalent of about 24 gallons of gasoline.

The compressed air from the tank is injected into the engine, where it expands and pushes down on a series of pistons that drive a crankshaft, which sets the car in motion. The compressed air itself contains no energy. Instead it is a "vector of energy," Vencat explains.

The copressed-air car's engine can supply the initial load of compressed air. When powered "in reverse mode" by electricity from a wall outlet, the engine becomes a compressor of ambient air ingested through an intake valve, and will fill the tank in three to four hours, Vencat says.

Alternatively, a compressed air station equipped with an industrial air compressor would be able to fill the tank with stored compressed air in two to three minutes, he says.

He envisions a nationwide infrastructure of local compressed air stations, much like today's array of corner gasoline stations.

According to the company's own tests with prototypes, the mono-energy air car offers a driving range of 100 miles per tank of compressed air when traveling at a speed of 20 mph, or 60 miles at a speed of 35 mph. Moreover, because air also is the only exhaust, MDI calls its mono-energy car a zero pollution vehicle.

Fuel-Burner For U.S.

That's not the vehicle the company plans to sell in the U.S., though.

Vencat says MDI plans to market - through a network of franchisees' factories that will sell directly to consumers - a "dual-energy" air car. It uses a secondary fuel in an external combustion chamber to heat the air in the engine, expanding it further and increasing both the top speed, to 96 mph, and the range.

With a 10-gallon fuel tank, the dual-energy vehicle will travel up to 1,000 miles between fill-ups, he says.

Also, thanks to a built-in viscosity sensor, Vencat says the secondary fuel can be anything from gasoline to vegetable oil.

It also is possible to run the dual-energy air car with a built-in auxiliary air compressor powered by the secondary fuel.

The auxiliary compressor would feed additional air to the expansion chamber at speeds above 35 mph, resulting in fuel efficiency of more than 106 mpg, the men claim. And in an "energy sharing" mode, some of this internally produced compressed air would be diverted to refill the storage tank as needed while the car is in motion.

At speeds below 35 mph, the dual-energy air car operates like its mono-energy sibling, not burning any of the secondary fuel and therefore emitting no pollutants. Even when it is burning the fuel at speeds above 35 mph, it will spew only 48-72 grams of CO2 per mile, depending upon the car's configuration according to MDI.

To date, the company has designed a variety of dual-energy models configured with two, three or six seats.

In the U.S. market, the company will emphasize the largest of these, a four-door six-seat car, which Vencat expects to sell for between $18,000 and $20,000. (In addition to his role as executive vice president of MDI, Inc., the wholly owned U.S. subsidiary of MDI SA in Luxembourg, he is CEO of Zero Pollution Motors based in New Paltz, NY - the company's first franchisee here.)

He anticipates selling at least 4,000 cars in the first year in the U.S.

Not A New Idea

The notion behind MDI's air car engine is not new. "This is an idea that's been around the better part of 100 years," notes Gale Banks, president and CEO of Banks Power, an Azusa, Calif.-based engineering firm that designs systems to boost the power and efficiency of auto and marine engines.

The only practical application of the technology, he adds, was in the early to mid-1900s, when locomotives powered by compressed air were used in the mining industry to move miners or equipment underground. "For the last eight to ten decades there were a variety of air car ventures. None of them became commercial."

The reason is simple, Banks says: Using compressed air to power a vehicle is inefficient.

To begin with, he explains, a compressed air engine loses efficiency in running the air compressor, and this is compounded by more efficiency losses in expanding the air in the engine.

Moreover, he says, the energy density of air is very low - lower than the energy density in a battery, which itself is lower than the energy density of gasoline or diesel fuel.

And low energy density translates directly into reduced range, which is why an electric vehicle will not travel as far on a charge as a gas- or diesel-powered car, if the weight of the fuel in its container is equal to the weight of the battery.

Burning fuel to heat the air is a way to overcome this range problem, Banks says, but he characterizes the solution as a "band-aid" and "an open admission that the pure air-powered car is inadequate." It is far more efficient to burn the fuel to power the car directly, he says.

"The internal combustion engine is going to be with us for a while longer. It's still a quite practical device, especially if you burn non-fossil fuels. You still have a carbon footprint, but you can diminish it," he adds.

Big Doubts

Banks - who also is a member of the X PRIZE rules committee - cautions that MDI's   inclusion in the contest's press conference at the New York Auto Show last March should not be construed as an endorsement of its technology.

The prize is reserved for current solutions to the fuel economy challenge, he says, noting that MDI has made claims without offering a vehicle to independent testers.

"I am tremendously skeptical of the claims and it remains to be seen whether or not they're valid. If they prevail in the X PRIZE, that will be the ultimate validation." 

All of Banks' assertions are echoed by Paul Vanvalkenburgh, an adjunct professor at California State University Long Beach. He taught a course there on hybrid electric vehicle engineering before retiring last year to work on "developing a simple low-cost hybrid electric-petroleum car for third world countries - pro bono."

MDI's compressed air engine is "primarily an energy storage and transport system, less efficient than batteries, and [with] less future potential," Vanvalkenburgh says. "It looks like all too-typical and common hype to raise venture capital" and "exploits consumer hope, and the quest of media for marketing sensationalism."

The company's claims have not been verified by a "respected and financially independent organization" and it has not delivered "running proof of promised performance," he says.

Jochem Wolschedorf, vice president of vehicle and drivetrain engineering at FEV, Inc., in Auburn Hills, Mich. says that an air car might have applications for "local driving," but says that. like Banks and Vanvalkenburg, he's concerned that MDI's clams for long-distance and high power "is at least questionable.  The math at the moment doesn't make sense to us."

FEV, the U.S. subsidiary of FEV Motoren Technik in Aachen, Germany) develops engines, powertrains and vehicles - including gas, diesel, electric and hybrid - for automakers and engine manufacturers worldwide.
 
"As an engineer, I still would like to see some real results" validating MDI's claims, Wolschedorf adds.

'Try It' Says MDI

Vencat responds to these critics with an invitation.

"To those who have doubts about what we claim, I would strongly suggest that they come and see for themselves what we have created at our research and development facility in Carros, France, before they make unsubstantiated criticisms."

Whereas an internal combustion engine is only 10 to 15 percent efficient on the highway and nine percent efficient in urban driving, the efficiency of MDI's compressed air engine is above 50 percent at all times, Vencat says.

Scores of engineers from Tata Motors - India's largest automobile company and the new parent of Jaguar and Land Rover - spent 30 months evaluating the technology at that company's expense, he adds.

There Are Merits

Apparently Tata did like what it found. In February 2007, the company signed a licensing agreement to deploy the technology and to provide an undisclosed amount of "financial support" for its further development, notes Debasis Ray, a Tata spokesman. (Rumors peg the amount at $30 million.)

The deal grants Tata the right to sell an air car only in India. However, Ray says, "We do not yet have any time-frame for launch."

Tata is the first auto manufacturer to enter the X PRIZE competition, and Banks calls its chairman, Ratan Tata, "one astute businessman." Nevertheless, he insists, "Tata looking at a technology means nothing more than they're looking at a technology."

If Tata were to commercialize an air car in India, Banks adds, that would be a far different marketplace and a far different car than in the U.S. - with Indian customers switching to the air car from motor scooters, not substantial cars.

"In markets such as India where people travel short distances and don't require high load carrying capacity, this technology may be viable. But in the majority of the industrialized world, I don't believe it will be,"  Banks says.

Jay Leno, the renowned auto collector and comedian, is another who likes the idea of the MDI air car. Although he has never driven one, he has learned about the development and calls it "brilliant technology, really smart," adding, "I hope it works."

He draws an analogy to the steam-powered cars in his collection , which includes a 1925 Doble Series E Steam Car that he says almost meets current emissions standards.

He is aware of the problems that plagued earlier air cars in the 1920s and 1930s, he says, and he believes that gasoline-powered engines are sure to be used for the next 30 years.

Still, Leno adds, "You never know what the future will bring. The last days of old technology are always better than the first days of new technology."

Posted by

John O'Dell October 13, 2008, 3:08 AM

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