Simultaneous Reduction of NOx and Particulate Emissions by Using Multiple Injections in a Small Diesel Engine

The diesel fuel injection system is the heart of the diesel engine and has become one of the critical emissions control technologies in recent years with the advance of electronically controlled fuel injection. The main objective of this study was to investigate the effect of pilot, post and multiple fuel injection strategies on engine performance and emissions. The study was carried out on a 4-cylinder 1.2-liter small-bore direct injection diesel engine equipped with a high pressure common rail fuel injection system. A large amount of engine performance, emissions, and cylinder pressure data over several engine operating points was obtained and analyzed. It was determined that use of pilot injection does not lead to a simultaneous reduction of NOx and particulate emissions unless optimized combinations of EGR rate, main injection timing, pilot injection timing, quantity and dwell before main injection were achieved. It was also found that post injection and multiple injections can reduce particulate emissions by more than 40% in some cases. It is believed that reduction of particulates using post injection or multiple injections is a result of improved particulate oxidation later in the combustion cycle due to increased in-cylinder bulk temperature and/or enhanced air/fuel mixing with the presence of an additional combustion event.