Abstract
The pre-mixed lean diesel combustion (PREDIC) has the possibility of significant reduction of both NOx and smoke emissions. The experimental results of PREDIC without after treatment have shown a NOx emission less than 20 ppm, a level which the conventional diesel engines have never achieved. PREDIC owes to the adoption of electronically controlled common rail fuel injection equipment, which can inject fuel at a scheduled crank angle and provide a good fuel and air mixture by using a pintle swirl nozzle. However, there is a big problem in PREDIC, that is, its output is only a half load of the naturally aspirated conventional engine. In order to obtain higher load, a supercharged and intercooled system has been adopted in a single cylinder engine for PREDIC. PREDIC's load conditions by high boosting are improved in three times higher than in the naturally aspirated (NA) condition. At the same time, the high boost condition causes the deteriorations of both THC and smoke emissions. The emission deterioration of PREDIC under the high boosting condition has been analyzed by using the high-speed photography of laser shadowgraph at bottom view type single cylinder visualized engine. Both the conventional and PREDIC up to the high boosting condition of 3.4 times of NA engine are studied in order to clarify the difference of boosting effects. The processes of mixture formation in both the conventional combustion and the PREDIC have been investigated by observations of combustion photographs. Under the high boosting condition the PREDIC's spray by pintle swirl nozzle does not spread widely and the mixture formation gets worse due to the high cylinder pressure. The PREDIC's mixture formation is more sensitive than the conventional combustion because PREDIC's injection timings are very early and its cylinder pressures vary fifty times from atmospheric pressure when the injection starts. So a better or more improved injection nozzle is needed than the current pintle swirl nozzle and it expects to make an appropriate mixture in several cylinder pressures, which widely vary fifty times from an atmospheric pressure.
