Abstract
Keywords:
Diesel engines, injection, combustion, emissions.
Abstract:
The characteristics of a two-stage combustion concept were investigated in a HD Diesel engine with the aim of reducing pollutant emissions. This combustion concept is generated by splitting the injection in two stages: one first early in the compression stroke and one second near TDC. Medium rates of external cooled EGR are necessary to control the rate of heat release and the NOx emissions levels. This strategy has been combined with two additional measures: increase in the swirl produced by the induction flow and post-injection. Tests have been carried out on a single-cylinder research engine, and computer aided studies have been performed by means of a diagnosis model and CFD calculations. The obtained information has shed light on the details of the spray evolution and combustion process. The results show that the soot emissions can be drastically reduced with respect to a plain combustion concept with a low increment in NOx emissions. An increase in fuel consumption, compared wit a plain single injection strategy was also observed. The optimisation of swirl level and the post-injection are able to further extend these benefit, and to mitigate the worsening in fuel consumption.