Cars could run on aluminium, say US boffins
'Violent poof' in Purdue lab inspires scientist
US engineering boffins believe they have found a way to make existing cars run on aluminium pellets.
The process involves generating hydrogen from water onboard the vehicle, which removes the need to store hydrogen in a tank. Fuel-tank design is one of the main challenges facing hydrogen car designers, and at present involves serious difficulties. The insulated cryogenic tank in BMW's Hydrogen Seven demonstrator car, as an example, will lose its entire contents to boil-off in matter of days. This doesn't just strand the vehicle (or compel its driver to use the backup petrol tank): it also means that a fuelled-up Hydrogen Seven can't be parked in an enclosed space, lest a dangerous buildup of explosive gas develop.
But boffins led by Professor Jerry Woodall of Purdue University reckon they've managed to sidestep this snag. In their process, water is combined with an alloy of aluminium and gallium. The aluminium oxidises, releasing gaseous hydrogen which could then be used to fuel a conventional car engine as in the Hydrogen Seven. The role of the gallium additive is to prevent a skin of oxide forming on the surface of the aluminium and allow all the metal to be used.
Woodall came across the reaction by accident in the course of research into semiconductors.
"I was cleaning a crucible containing liquid alloys of gallium and aluminum," he says. "When I added water to this alloy - talk about a discovery - there was a violent poof."*
The only exhaust from a hydrogen-fuelled car engine would be water vapour. However, waste aluminium oxide (or alumina) and gallium would also be produced in this case.
"The gallium doesn't react," says Woodall. "So it doesn't get used up and can be recycled over and over again."
The alumina would also be recycled under Woodall's plan, using a process called fused salt electrolysis. This requires large amounts of electricity (as does the initial production of aluminium from bauxite), so the overall process is essentially a way of storing electric power in aluminium pellets and releasing it as hydrogen at the point of use.
Aluminium at the moment costs $1 per pound, which according to Woodall means that an aluminium/gallium/hydrogen car would cost more to run than than an ordinary one using petrol at $3 to the gallon. But he reckons that recycling the waste alumina at nuclear powerplants would bring the costs down. Cutting out electrical power distribution would enable the juice to be used more efficiently.
"A midsize car with a full tank of aluminum-gallium pellets, which amounts to about 350 pounds of aluminum, could take a 350-mile trip and it would cost $60, assuming the alumina is converted back to aluminum on-site at a nuclear power plant," said the professor.
"How does this compare with conventional technology? Well, if I put gasoline in a tank, I get six kilowatt hours per pound, or about two and a half times the energy than I get for a pound of aluminum. So I need about two and a half times the weight of aluminum to get the same energy output, but I eliminate gasoline entirely, and I am using a resource that is cheap and abundant in the United States. If only the energy of the generated hydrogen is used, then the aluminum-gallium alloy would require about the same space as a tank of gasoline, so no extra room would be needed, and the added weight would be the equivalent of an extra passenger, albeit a pretty large extra passenger."
And converting existing cars wouldn't be too difficult, according to Woodall.
"It's a simple matter to convert ordinary internal combustion engines to run on hydrogen," he says. "All you have to do is replace the gasoline fuel injector with a hydrogen injector."
The process could also potentially be used in combination with hydrogen fuel-cell technology to great advantage.
"When and if fuel cells become economically viable, our method would compete with gasoline at $3 per gallon even if aluminum costs more than a dollar per pound," says Woodall.
More details from Purdue here. ®
*From the hydrogen exploding, we assume