1. INTRODUCTION
Internal combustion engines are today the dominating propulsion technique for ground vehicles. Over the past century the engine development has undergone different stages driven by commercial and legislative requirements. During the past 30 years legislation has dictated lower and lower emission levels and the development has lead to a significant reduction in the emission of Nitric oxides (NOx), carbon oxide (CO), hydrocarbons (HC) as well as soot and particles (PM). This has lead to a positive effect on the air quality in cities although the number of driven vehicle kilometers has increased [3]. For gasoline engines the usage of the three way catalytic converters and electrically controlled injection systems has drastically reduced the emission of the exhaust gases listed above. In the near future legislation will require even lower level of emissions.