Abstract
The increase of road transport has created, the problem of air pollution from exhaust emissions. The air quality of large cities should be improved especially in Europe. Based on the air quality targets given by the WHO, the NO2-concentration in urban areas should be reduced by all means. The reduction of particulate, aldehyde and carcinogenic HC-emissions is also important, because of their proven injurious effect to health. A connected issue is the energy supply of road vehicles, because they consume a large amount of energy mainly in the form of petrol and diesel fuel. One of the solutions is an environmentally clean fuel, which offers, in addition, an opportunity for energy diversification. Natural gas is a lower cost fuel than petroleum based products, and this cost advantage is expected to continue in the future.