automobiles" (Bockris and Was, 1988, WWW). So the key problem is to find a way to store hydrogen in a safe and dense way. The solution is probably in metal hydrides. Metal hydride represents a special way of storing hydrogen atoms in a special metal grid, wherefrom hydrogen can be evolved at any time. Almost two times more hydrogen atoms could be stored this way in the same sized tank, but the whole system is very heavy because of the metal included in the hydrogen tank. BMW and Mazda are demonstrating that it is anyway possible to run a hydrogen-powered car that is reliable and safe. BMW operates an experimental BMW 745hi ("hi" for hydrogen injection) vehicle that has a hybrid engine able to burn liquefied hydrogen as well as gasoline. "This vehicle is equipped with a 75 kg liquid-hydrogen tank with energy equivalent of 40 liters of gasoline and has a cruising range of 400 km, or fuel efficiency of around 10 km per liter" (2000, BMW official web page). Mazda is the pioneer of hydrogen use in internal combustion engines. According to Mazda's homepage (2000, WWW) now there are three experimental vehicles operated by Mazda. First project of Mazda was a small Mazda HR-X van that just successfully completed a two years trial period. This car was lent to Hirohata Steel Mill for use as their company van and drove at least 20 000 kilometers on public roads. This vehicle uses pressurized, but not liquefied, hydrogen as the only fuel. The second car was the HR-X2, with the same chassis and engine but with a new fuel tank storing the hydrogen in its hydride form. This greatly improved the amount of stored hydrogen and increased its economy and cruising range. The last Mazda's hydrogen powered project is the popular roadster Mazda MX-5 powered by hydrogen and a fuel tank using the hydride advantages. All these cars are about 400 kg heavier than the standard models; this is mainly because a 300 kg hydrogen tank was installed instead of a 50 kg fuel...
