In order to obtain a simultaneous reduction in both NOx and particulate emissions from a direct injection (DI) diesel engine, an advanced combustion system has been researched and developed in the authors' laboratory. The new combustion system comprises homogeneous charge compression ignition (HCCI) combustion at low load by early and multiple injections, combined HCCI, and lean diffusion burning at medium and higher load conditions by means of a novel combustion chamber design and multiple injections. In this paper, the research and development of the enhanced mixing by means of a raised round object (referred to in this paper as BUMP) and its application to a diesel combustion chamber design is described. Then the experimental results from a DI diesel engine equipped with a multiple injection common rail (CR) fuel injection system and the new combustion chamber design will be presented and discussed. Engine testing has shown that the BUMP combustion chamber was very effective in reducing both NOx and smoke emissions. HCCI combustion by means of multiple injections leads to extremely low NOx emissions under low load operations. At medium and higher load operation conditions, quasi HCCI combustion combined with the BUMP combustion chamber could signficantly reduce NOx emissions without sacrificing particulate emission and fuel consumption.
