BMW CleanEnergy vehicles have both a hydrogen and a petrol tank. If one of the tanks is empty, the bivalent BMW engine unit switches over automatically to the other fuel system. One decisive advantage of the combustion engine is bivalence. It enables both hydrogen and petrol to be used, thus creating the ideal conditions for a transition from non-regenerative to regenerative drive energies. During electrolysis water is split into its components of hydrogen and oxygen. The hydrogen is stored and the oxygen is needed in the vehicle for the combustion of the hydrogen. The combustion process generates energy and water as a waste product, which returns to the natural water cycle. And so with the aid of regenerative energy suppliers, an emission-free fuel is obtained. BMW AG (an abbreviation of Bayerische Motoren Werke AG, or in English, Bavarian Motor Works), is a German company and manufacturer of automobiles and motorcycles. ... A fuel cell powered vehicle from GM A hydrogen vehicle is an automobile which uses hydrogen as its primary source of power for locomotion. ... Gasoline, as it is known in North America, or petrol, in many Commonwealth countries (sometimes also called motor spirit) is a petroleum-derived liquid mixture consisting primarily of hydrocarbons, used as fuel in internal combustion engines. ... Bivalent (chemistry): two or more atoms bound together as a single unit and forming part of a molecule An atom which can form two covalent bonds with other molecules (such as oxygen) is said to be bivalent, posessing a valency of 2. ... An engine is something that produces some effect from a given input. ... In logic, the principle of bivalence states that for any proposition P, either P is true or P is false. ... In chemistry and manufacturing, electrolysis is a method of separating bonded elements and compounds by passing an electric current through them. ...