Angela Graham, of Waihopai School, asks :-

Can cars run on water?

Roger Green, a mechanical engineer at the University of Canterbury, responded.

Car engines cannot run solely on water. However, water can influence the performance of an engine. There are two ways.

Firstly water can be used to give a petrol engine more air. This is done by injecting small amounts of water into the air before it passes into the engine cylinder. This water evaporates, and as it does so it lowers the air temperature. The density of the air is increased and a greater mass of air enters the engine. More air means that more petrol may be burnt and the power produced by the engine is increased.

The second method helps engines to run on poor quality petrol. The water is injected directly into the engine cylinder whilst the petrol flame is burning and the water cools the combustion process. The output power of the engine is reduced, but the engine does run satisfactorily.

Finally engines can be run on hydrogen (instead of petrol) and hydrogen is produced from water. This is done by passing an electric current through water and producing hydrogen and oxygen. Hydrogen is an ideal fuel because it is very clean burning, producing only very small amounts of pollution. But because of problems of cost, storage and safety, it will be some time before hydrogen fuelled cars become common.