From rocket fuel to clean cars

Liquid hydrogen-powered combustion engine
7 November 2012
Hydrogen, the lightest of all gases, is the most common element in the Universe. It is extremely easy to burn, if oxygen is present. Used in Europe’s Ariane 5 launchers, hydrogen is an excellent rocket fuel, but it is very hard to store. It must be kept in double-walled tanks at very low temperatures, then fed to the rocket engines through tightly sealed pipes.
Recent advances by an Austrian company suggest that hydrogen may also become the fuel of choice for future road transport, solving the problem of how to create clean cars. Working with the German carmaker BMW, this company has adapted rocket technology to develop hydrogen storage tanks small enough to fit in the boot of a saloon car. In 2007, this led to the birth of a production car, the BMW Hydrogen 7, which can use either hydrogen or petrol as fuel. Essentially the only waste emission from the car is harmless water vapour!
Liquid hydrogen highly insulated fuel tanks for BMW Hydrogen 7
Hydrogen car fuel tank
One of the major challenges was designing the fuel tank. To store as a liquid, hydrogen must be kept at –253ºC. Instead of using constant refrigeration, BMW Hydrogen 7 cars store 114 litres of liquid hydrogen in highly-insulated tanks. Equivalent to a 17 m thick layer of Styrofoam, the tanks’ insulation can keep the hydrogen cold for almost two weeks.

There are still some problems to be overcome before hydrogen-fuelled cars become commonplace. One is the lack of fuelling stations. Another is the loss of liquid hydrogen when it warms and slowly boils off as a gas. A driver leaving the car at the airport for two weeks for example, would return to an empty fuel tank. However, there are clear signs that clean cars fuelled by hydrogen are the future of pollution-free motoring.

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