At the beginning the theoretical part of the diploma thesis deals with a characteristic of fuels for ignition engines, namely to automotive petrol and a mixture of liquid petroleum gases (LPG). The next part is focused on a description of conversions of individual elements which are necessary for cars which operate on alternative fuel. As well the attention is paid to the production of emissions of exhaust fumes of these engines, to individual components of unwanted emissions, their formation and effect to people and the environment. The own thesis introduces a proper measurement of Subaru Forester car, converted into the two fuel car which is possible to work both on petrol and LPG. Operational parameters for particular fuels were observed on the tested car.