For last several decades, there has been a lot of research about DI (Direct Injection) diesel engines because they have a clear advantage in terms of CO2 (Carbon Dioxide) emissions compared to gasoline engines. Furthermore, because of its ability to operate at low equivalence ratios, the diesel engine produces lower CO (Carbon Monoxide) and HC (Hydro-Carbon) emissions. Unfortunately, the diesel engine suffers from relatively high NOx (Nitrogen Oxides) and PM (Particulate Matter) emissions. In diesel engine research, keeping low fuel consumption in all operating conditions and reduction of PM and NOx emissions, are both critically important problems which need to be addressed. For this reason, research about diesel engines is being actively pursued in recent times. PM and NOx could be considerably reduced using low temperature combustion under part load conditions. But, further investigation is also necessary for fuel consumption and emission reduction under high load conditions. Reduction of orifice diameter, multiple injections and high pressure injection are avenues of rigorous research with the injection systems evolving rapidly. Fuel consumption and emission of PM are improved by using high pressure injection due to better air-fuel mixing while there are still problems with NOx under all operating conditions and insufficient reduction in PM emissions under high load conditions. Diesel engine noise and up to some extent, PM and NOx emissions are reduced by the use of multiple injections. However, the reduction achieved by multiple injections is not enough to satisfy the regulations on emission which are becoming more and more stringent. Reduction in diameter of orifices has some positive effects, such as significant reduction of PM and improvement in air-fuel mixing through better atomization and evaporation. On the other hand, it also has a negative effect under high load conditions, which is the reduced spray tip penetration with high temperature and pressure in combustion chamber.weiterlesen