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The NOx reduction by low temperature EGR and low compression ratio were investigated to develop EU6 diesel engine for heavy weighted SUV vehicle. A low temperature EGR is to reduce EGR gas temperature by cold EGR coolant, thus it can decrease NOx at same PM emission. A low compression ratio can improve NOx due to low combustion temperature. These two methods have advantages in practical application, because it could be easily adapted to conventional diesel engine. On the other hand, some possible problem such as EGR fouling and poor cold start-ability might be caused when EGR coolant temperature and compression ratio are reduced too much. It is necessary to find the NOx reduction effect without these abnormal phenomenons. The results showed that low temperature EGR made more remarkable NOx reduction rate at low load condition where had low EGR flow. It could decrease NOx by around 4% at NEDC 14 modal points.

The characteristics of diesel spray injected into the cylinder provide crucial clues to the perception of the combustion performance in a compression ignition engine. In this study, five different diesel common rail injectors were examined which have different hole numbers, orifice sizes, jet cone angles, and hydraulic flow rates. Both the macroscopic and microscopic characteristics of diesel sprays were compared through Mie-scattered light imaging and PDA (Phase-Doppler anemometry) measurements. Seven hole injector with smaller hole was found to give better air/fuel mixing and favorable droplet size compared with other injectors. To evaluate the feasibility of achieving lower emission level with the different diesel sprays, the combustion and emission characteristics in case of 6 and 7 hole injectors were investigated under the same fuel flow rate condition in a light duty DI diesel engine.