Toyota's Prius has become a standard-bearer of sort for the green machine movement. Buyers who were looking for technologically advanced vehicles with good fuel economy latched on to the Prius - and have so in larger numbers since its 1998 introduction. Now, Toyota is planning the third generation of its bleeding-edge hybrid, with a concept due at the Geneva motor show that might show the way to the next evolution of the Prius. But what if the Prius were to become radically different? What if it were to adopt a new powertrain - one fueled by hydrogen?
One company is working on just such an experimental Prius - ECD Ovonics, a battery and hydrogen-storage technology company headed by former General Motors chairman Robert Stempel. TheCarConnection took ECD's offer of driving their experimental Prius recently, and in its current state of development, a hydrogen Prius doesn't seem to be too far a stretch of technology's imagination.
Hydrogen on board
We slide into the Ovonic Toyota Prius, stock-appearing but for bold "Hydrogen Hybrid" graphics. Our passenger is Jeff Schmidt, assistant chief engineer on this project who helped install the hydrogen fuel system. Schmidt tests the car on and off the road and drives it 43 miles home and back almost daily.
The company's H2 storage system contains a proprietary mix of powdered metals that absorbs gaseous hydrogen under pressure, stores it as solid metal hydride, then releases it on demand when heated. "We store 3.6 kilograms (kg) of hydrogen in two 33-liter vessels, which provides a 200-mile range," he points out. "The same-size tank of gaseous hydrogen compressed at 5000 psi will hold about 1.6 kg, which gives about an 80-mile range."
The car's hydride tanks are refueled at 1500 psi (pounds per square inch) in five to eight minutes, the pressure drops to about 300 psi. "So the system needs to be much less robust and is much less prone to leaks compared to a high-pressure system," Schmidt asserts.
The bolt-on conversion from gasoline to H2 is relatively simple. The twin hydride tanks replace the gas tank without affecting cabin or trunk room. Since the gaseous hydrogen burned in the cylinders contains substantially less energy than the equivalent liquid gasoline, the Prius' 1.5-liter four is turbocharged and intercooled to restore its performance to gasoline levels. A gaseous fuel delivery system, including manifold, injectors and fuel rail, replaces the liquid system, but no internal engine modifications are needed. Heat exchangers inside the tanks release hydrogen; its pressure is stepped down to 150 psi at the engine then regulated in the manifold and injected into the cylinders at 18 to 38 psi. MORE--
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