It’s the Hybrid Air — an experimental vehicle that the French automaker PSA Peugeot Citroën has been trumpeting lately as an exemplar of energy efficiency. While some skeptics doubt whether it is truly breakthrough technology, the Peugeot and Citroën concept cars containing it may prove to be some of the more intriguing models on display next week at the Geneva Motor Show.
Peugeot says a compact car like a Citroën C3 equipped with the technology will get about 100 kilometers per 2.9 liters, or 81 miles per gallon, in city driving. If so, that would be significantly more than existing hybrid electric vehicles like the Toyota Prius can achieve in stop-and-go traffic.
Peugeot, the second-biggest carmaker in Europe after Volkswagen, plans to begin rolling out Hybrid Air cars by 2015 or 2016.
Like a Toyota Prius, the Hybrid Air recovers energy each time the driver brakes or decelerates. But instead of using that braking energy to charge a battery, which then runs an electric motor — as in the Prius — the Hybrid Air has a reversible hydraulic pump that uses the braking energy to compress nitrogen gas in what looks like an oversized scuba tank. When the Hybrid Air driver next presses the accelerator, the compressed gas pushes hydraulic fluid, syringe fashion, through a gearbox to turn the wheels.
The energy stored in the nitrogen tank is small — equivalent to only about five teaspoons, or a couple dozen cubic centimeters, of gasoline — and enough to power the car only a few hundred meters before the standard gasoline motor takes over again. But repeated over the course of a day of city driving, Peugeot says, those extra teaspoons of energy add up to big improvement in gas mileage.
The idea of using so-called hybrid hydraulics to power a car has been around for a while, although Peugeot prefers to call it “hybrid air technology” because the energy is stored in the compressed gas, rather than the hydraulics. In the United States, Ford Motor and Chrysler have studied the approach with encouragement from the Environmental Protection Agency. UPS, the parcel service, has added several dozen hybrid hydraulic delivery vans to its alternative fuel fleet. Other companies are applying the technology to garbage trucks, which like UPS vans, are big, make frequent stops and stand to recover much of their wasted energy. The Indian auto company Tata has promised to produce a car powered solely by compressed air, although that uses a different technology than Peugeot’s approach.
Peugeot, with a 200-member Hybrid Air team led by Karim Mokaddem, an engineer, appears to be moving the fastest of any global automaker to bring the technology to the family car, while most of the industry has focused on hybrid electrics as the main alternative vehicles for reducing emissions and saving gasoline.
“The logic of an electric hybrid is completely different,” Andrés Yarce, another of the project leaders, said in Peugeot’s technical center in Carrières-sous-Poissy, near Paris. With an electric hybrid, “you let the vehicle run for a few kilometers, have the engine shut off, then run silently on an electric motor,” Mr. Yarce said. “It took time for people to grasp that the Hybrid Air works differently but gets the same results.”
When the car is ready for the market, Peugeot plans to price it below €20,000, or $26,000.
Mr. Mokaddem said the pricing was meant to make the Hybrid Air a viable option in emerging markets like China and India, where many hybrid electrics are too expensive for most consumers and too complex for local service and repair operations.
Peugeot says it can undercut hybrid electrics on price because its car does not require a special, expensive battery and electric motor that vehicles like the Prius use, although the Hybrid Air does employ a standard car battery. The hydraulic system also adds about 100 kilograms, or 220 pounds, to the weight of a conventional Citroën or Peugeot. And because of the heat generated by the energy transfer process, the designers have had to adapt the car’s cooling system.
The most obvious difference between the prototype Hybrid Air and an ordinary car is the presence of two air tanks (the second, smaller tank is a low-pressure receptacle) and a special gearbox that manages the energy handoffs between the hydraulics and the 1.2-liter standard gasoline engine. The designers say the setup left them room to keep a standard-size trunk and gas tank.
The accumulator, or pressurized nitrogen tank is 1.3 meters, or about 4 feet, long, with a volume of 20 liters, or 5.3 gallons, and a maximum pressure of 250 bar, or about 3,600 pounds per square inch.