The development of the automobile at the end of the nineteenth century fundamentally changed the structure of society in the developed world and has had wide-ranging effects on the environment, the most notable being the increase of air pollution in cities. The piston-type internal combustion engine is responsible for the peculiar mix of pollutants that it generates. There are a range of other engines suitable for automobiles, but they have yet to displace engines using rather volatile petroleum derivatives.

The simplest and most successful way of improving gaseous emissions from automobiles is to find alternative fuels. Diesel fuels have always been popular for larger vehicles, although a few private vehicles in Europe are also diesel-powered. Compressed natural gases have been widely used as fuel in some countries (e.g., New Zealand), while ethanol has had a limited success in places such as Brazil, where it can be produced...