The Contribution of the Fuel Injection System to Meeting Future Demands on Truck Diesel Engines

Based on fundamental findings on mixture formation and combustion in Diesel engines, guidelines can be defined for further development of combustion systems with low exhaust and noise emissions. For the first combustion phase, these guidelines require the combustion of small fuel quantities to limit primary soot and NOx as well as combustion noise. In the second phase (Until end of injection) sufficient mixing of air and fuel is imperative to avoid formation of secondary soot and HC. In the third phase (after end of injection) intensive mixing of air and burned gases is necessary for the soot oxidation. The fuel injection system occupies a key position to fulfill, these requirements and, thereby, meet future demands with regard to exhaust and noise emissions.

In this connection, results of experimental investigations with a single-cylinder four-valve engine have been analysed. The engine has been operated with different fuel injection systems incorporating conventional high pressure pump-line-nozzle configurations, injection pumps with very high pumping rates and unit injectors with electronic spill control. The latter also offered the possibility to obtain split injection. Apart from the influence of the injection rate, the significance of injection timing control will be demonstrated. The effects of split injection on combustion noise and exhaust emissions will also be considered.