DEVELOPMENT OF THE COMBUSTION CONCEPT OF THE ALFA ROMEO JTS DIRECT INJECTION GASOLINE ENGINE

摘要

For the development of the combustion system of the Alfa Romeo JTS engine (Jet Thrust System) a new concept was chosen, different from the stratified/lean burn approach for a relatively large operation window followed by most competitors and also different from the completely homogeneous lambda=1 approach, selected by others. The Jet Thrust System allows to reach the good full load performance of the latter, combined with relatively good fuel economy at speed and loads near to idle due to stratified charge operation, typical of the first approach. The important characteristic of the system is that no lean NO{sub}x after treatment catalysts are necessary and no special low sulphur fuel is mandatory for its functioning. To develop the system up to production status an integrated development approach was followed based on CFD calculations, experimental studies using engines with optical access and bench testing with advanced pressure indicating techniques. It is thanks to this integrated approach that it has become possible to maximise both performances and fuel efficiency of the combustion system, and in the meantime to reduce the sensitivity to production tolerances. It can be stated that without this integrated approach and the availability of the new advanced tools, the successful exploitation of gasoline direct injection engine would have never been possible.