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TCC Drives A Hydrogen Prius


 

 

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--

 

 

Stempel’s vision

 

ECD Ovonics chairman and CEO (and former General Motors CEO) Robert C. Stempel is high on the long-range potential of hydrogen-powered vehicles to jump-start development of the infrastructure that will be needed to support fuel-cell vehicles.

 

“I think fuel cells are still a ways off, given their expense and other issues,” he says, “but there’s a lot of pressure to do something about CO2. When you run on hydrogen, there’s virtually no CO2 because there’s no C in H2. That is a significant plus.

 

“The hybrid is an ideal application, and we’ve been able to show that you can get virtually the same performance, car to car. We’ve had to do some things like adding a turbocharger, but the electric motor at the low end provides the torque we need to get off the line. We’re at about 200 miles of range now, and we’re changing our metal hydrides to get it up to maybe 300 miles. It’s a pretty heavy development program for us, but we think there are things we can do with those materials to get the mass down and the capacity up.”

 

Because the tanks are packed with powdered metals, they’re not only heavy but -- like an electric vehicle’s batteries -- also expensive relative to a tank of gas. “Obviously, we have plans to bring the cost down,” Stempel adds, “but it’s pretty tough to get it to gas-tank cost.”

 

One major advantage of solid hydrides vs. gaseous storage is safety. “We’re authorized by the DOT to transport hydrogen in hydride containers anywhere in the U.S. or Canada , with no restrictions,” Stempel points out. “You can’t do that with high-pressure hydrogen. We’ve also been told we could put hydride tanks at corner gas stations. And you can refill them yourself. There is an interlock, so when you put the nozzle on and close a cover, it knows it’s there and secure or it won’t start the flow. Once properly connected, it’s very easy.”

 

Schmidt says the experimental H2 Prius hybrid’s fuel efficiency are close to those of a fuel cell vehicle. Its hydrocarbon (HC) and carbon monoxide (CO) emissions are near zero, and its carbon dioxide (CO2) -- not a pollutant (we breath it out; plants breath it in) but a prime suspect in global warming theories -- are just 1.6 grams per mile (gpm) from trace amounts of lubricating oil burned in the engine. That compares to 176.5 gpm from a standard Prius. “NOx is a bit higher,” he says, “because we’re pushing several times the volume of air with the turbo compared to naturally aspirated. We can bring that down with calibration.”

 

A change in the air?

 

Driven conservatively, the H2 Prius performs much like the standard variety. The electric motor provides decent torque for launch, the engine adds velocity on demand, and the combination cruises normally at normal speeds. When asked for maximum surge, the electric CVT transmission does its best impression of a centrifugal clutch, rushing the engine to high rpm while the car picks up speed more gradually. Schmidt says the turbocharged H2 engine pumps out 72 hp, slightly more than the gas-powered Prius, “but the torque and power curves are a little different, so we allow the engine to spool up a little higher.”

 

On the warm day we drove the car, we found that repeated wide-open-throttle runs can temporarily draw the NiMH battery pack’s power down to where it contributes little to low-end oomph. By the time we tried a couple of informal stop-watch runs, the battery was tired enough that acceleration from rest to 60 mph consumed nearly 20 seconds. “If the battery runs down too much,” Schmidt explained, “the system starts to kick the battery out because it doesn’t want to run it dead.” A healthy gas-powered Prius can do zero-to-60 in half that time.

 

We don’t believe hydrogen as a motor fuel -- outside of small captive fleets with centralized refueling -- is close to prime time, but we applaud the efforts of ECD Ovonics and others (notably including Ford and BMW) to develop and put it on the road in experimental and low-volume fleet and consumer vehicles. Whether volume fuel-cell EVs are ready in five years or 20, then is not the time to begin preparation of the hydrogen fuel infrastructure.

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