The role of in-cylinder gas density and oxygen concentration on late spray mixing and soot oxidation processes

An analysis of in-cylinder gas density and oxygen mass concentration (YO 2 ) impact on the mixing and oxidation processes and the final soot emissions in conventional high temperature diffusive Diesel combustion conditions is presented in this paper. Parametrical tests were performed on a single cylinder heavy duty research engine. The density was modified adjusting the boost pressure following two approaches, maintaining the YO 2 either before or after the combustion process. The YO 2 was modified by diluting fresh air with exhaust gas maintaining a constant density. The possibility of controlling the soot emissions combining both parameters (YO 2 and density) is evaluated and, in a final part, the NO X emission results are also addressed. Results show that YO 2 has a strong effect on both mixing and oxidation processes while density affects principally the mixing process. Both parameters affect the final soot emissions. The density modification through adjustment of boost pressure modifies the trapped mass and has a strong impact on the evolution of YO 2 (thus on the evolution of the mixing process) during combustion. If the density is increased maintaining constant the YO 2 at the beginning of the combustion, the NO X -Soot trade-off is enhanced.