Flywheel and compressed air hybrid cars

Alternative hybrid approaches replace the battery with compressed air or a flywheel.

Compressed Air

Scuderi has now released results of a computer simulation of its compressed air engine against a European economy-class engine of comparable power. The compressed air hybrid achieved a fuel economy figure of 65 miles per gallon, compared with 52 miles per gallon for the conventional engine. It also emitted 85 grams per kilometer of carbon dioxide, compared with 104 grams per kilometer for the conventional engine.

Scuderi, based in West Springfield, Massachusetts, has altered the way the internal combustion engine operates to convert kinetic energy into the potential energy of high-pressure air. It splits the four parts of the internal combustion cycle across two cylinders synchronized on the same crankshaft. One cylinder handles the air intake and compression part of the cycle, pumping compressed air via a crossover passage into the second cylinder. The crossover contains the fuel-injection system, and combustion and exhaust are handled in the second cylinder.

When the vehicle does not need power—when traveling downhill, braking, or decelerating—the second cylinder is disabled and the first cylinder’s air is diverted into a high-pressure air-storage tank. This air can be used to help run the engine, boosting its efficiency.

Scuderi has combined this system with a “Miller-cycle” turbocharger, which picks up energy off the exhaust and uses it to compress air into the intake cylinder. This allows the compression side to be shrunk down and reduces the amount of work done through the crankshaft.

Direct Energy to and from the wheels Flywheel

The Renault Formula 1 team has adapted its motorsport-developed flywheel system for use with conventional vehicles. The team has formed a company, Flybrid Systems, to commercialize the technology, and has teamed up with Jaguar Land Rover to trial the Flybrid technology that was originally developed as the kinetic energy recovery system (KERS) used in Formula 1 racing to provide a boost during racing. But while most KERS systems work by using a flywheel to charge an onboard battery or supercapacitor, Flybrid uses a gearbox system to transfer kinetic energy directly to and from the wheels.

Flybrid cars transfer energy via either a continuously variable transmission or a less complex three-gear system, which allows 15 different gear ratios on a standard five-gear model. “There are always efficiency losses when you convert energy,” explains Flybrid’s technical director, Doug Cross. “This system eliminates those losses, making it far more efficient.”

The flywheel weighs five kilograms and is made from carbon fiber wrapped around a steel core. Because it is so light, it has to spin fast—at 60,000 rpm—which means that its rim is traveling at supersonic speeds. As a result, it has to operate in a vacuum, and Flybrid has developed special seals so that the wheel can be fully enclosed inside a safety container in case of a crash. At top speed, the flywheel can store 540 kilojoules of energy, which is sufficient to accelerate an average-sized automobile from a standing start to 48 kilometers per hour.

“One way you can use this technology is to boost the car during a cruise,” Cross said. “We have a system installed on a Jaguar saloon, and that has shown that during a cruise, you can actually switch the engine off for 65 percent of the journey. With a V6 diesel engine, it cuts fuel use by 26 percent, but gives you the power of a V8 petrol engine.

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