Study on the fuel spray and combustion of the variable orifice nozzle (VON) for direct injection diesel engines

摘要

The government has been imposing a stricter diesel engine efficiency standard to reduce carbon dioxide, NO{sub}x and other particulate emissions. Diesel combustion improvement is a major concern, and many researchers have examined diesel combustion and its sprays. One possible method to solve the technical problems is applying the Variable Orifice Nozzle (VON) to fuel injection systems. The VON, which nozzle cross-sectional area is changed continuously, has been developed for direct injection (DI) diesel engines. The orifice changing mechanism is composed mainly of a rotary valve, drive shaft and small pulse motor. The VON's standard deviation (SD) of injection quantity in injection pump operation range is the same as the conventional hole nozzle's due to the rotary valve that is fixed by a spring. The smaller orifice of the VON has produced a higher injection pressure and produced a longer injection duration than that of a larger orifice. The VON was installed and its capability demonstrated on a single cylinder research engine. The injection spray of the VON in a high-pressure chamber, which was at the same condition as the combustion chamber of the engine, was observed by high-speed camera. In the smaller orifice case, the exhaust gas and combustion noise on the engine was improved compared with the larger orifice in the part and medium load range. The smaller orifice spray of the VON in the high-pressure chamber has produced wider spray angle than in the larger orifice case. At the same time, spray pattern was kept axisymmetric.