Air hybrid cars could halve fuel consumption

Researchers are exploring air hybrid automobiles as possible alternatives to electric hybrid cars, claiming they could be more efficient and less expensive to manufacture.

Suzanne Deffree, Managing Editor, news -- EDN, March 17, 2011

Researchers in Sweden are exploring air, or pneumatic, hybrid automobiles as possible alternatives to electric hybrid cars.

The research is based on the fact that energy is generated every time a car brakes. The researchers believe that manufacturers can save this energy for later use in the form of compressed air. The engine then gets extra power when the driver starts the car, which saves fuel by avoiding idling when the car is at a standstill. The concept is similar to that in electric cars and electric hybrid cars, which use brake energy to power a generator that charges the batteries.

According to Per Tunestål, a researcher in Combustion Engines at Lund University in Sweden, air hybrids would be less expensive to manufacture than electric cars and electric hybrid cars. Although these ait hybrid vehicles are not yet in production, the step to commercialization need not be large, the researchers from the university claim.

"The technology is fully realistic. I was recently contacted by a vehicle manufacturer in India which wanted to start making air hybrids," Tunestål said in a statement.

The technology is particularly attractive for stop-and-go and slow driving, for example buses in urban traffic.

"My simulations show that buses in cities could reduce their fuel consumption by 60%", said Sasa Trajkovic, a doctoral student in Combustion Engines at Lund University who recently defended a thesis on the subject. Trajkovic adds that 48% of the brake energy, which the technology compresses and saves in a small air tank connected to the engine to be reused later. This means that the degree of reuse for air hybrids could match that of today's electric hybrids.

The researchers developed a pneumatic hybrid-vehicle model in The MathWorks' Matlab and Simulink tools. The engine part of the vehicle model comprises engine data from Gamma Technologies' industry-standard GT-Power model for engine simulation. Vehicle-drive-cycle simulations show that the technology could reduce the fuel consumption by as much as 58% below that of a conventional bus.

The researchers gave no information on what materials were used in these simulated air hybrid engines, only stating that such an engine does not require any expensive materials to manufacture and that they have smaller footprints than electric hybrids. The method works with petroleum, natural-gas, and diesel fuel, they said.

The Lund researchers worked with the Sweden-based valve control systems company Cargine on the research.

The idea of air hybrids is not a new one. Indeed, Ford explored air-hybrid cars in the 1990s, but shelved the plans because it lacked the necessary technology to move forward with the project. Research on air hybrids is now being conducted at ETH in Switzerland, Orléans in France, and Lund University in Sweden. One company that intends to invest in engines with air hybrid technology is the American Scuderi. However, the Lund researchers point out that the only results so far have been from simulations, not from experiments.

"This is the first time anyone has done experiments in an actual engine," Tunestål said. "The research so far has only been theoretical. In addition, we have used data that means we get credible driving cycle results, for example data from the driving patterns of buses in New York."

The researchers in Lund hope that the next step will be to convert their research results from a single cylinder to a complete, multi-cylinder engine. Doing so, they said, would move the concept one step closer to a real vehicle.

 

*Editor's note: This story was updated to include content on the pneumatic hybrid-vehicle model, contributed by Fran Granville.

Lund University