Abstract
Direct Injection operating stratified is well accepted as the most efficient single technology for fuel consumption reduction with gasoline engines. However, the compliance with future exhaust emission legislation requires the application of a complex lean exhaust gas aftertreatment, reducing the cost efficiency of first generation GDI systems significantly. Besides the development of second generation GDI (spray guided combustion systems) with improved fuel consumption and HC- emissions, also refinement and development of new homogeneous GDI combustion systems are very attractive approaches.
Homogeneous auto ignition shows similar fuel efficiency as stratified GDI systems at part load and offers lower HC and nearly negligible NOx-emissions. The key challenges are system simplification and precise control of auto ignition during real world transient operation where the application of direct injection plays an essential role.
Another very interesting alternative for fuel economy improvement is downsizing combining turbocharging with spark ignited homogeneous direct injection. Utilising the advantages of direct injection like improved knock resistance and consequently higher applicable compression ratios, refined mixture preparation at increased back pressures, enhanced charging behaviour at low engine speeds, etc., results in very attractive driveability and fuel economy improvements. For extreme downsizing the application of an additional E-booster will be necessary.
The selected engine technologies, however, will be strongly determined by the respective combination of engine, transmission technology and the vehicle itself, so that in future different gasoline engine technologies will be applied in parallel.