THE SPRAY STRUCTURE OF AIR-SHROUDED DUAL-STREAM PORT FUEL INJECTORS WITH DIFFERENT AIR-MIXING MECHANISMS

An experimental study of the spray structure from air-shrouded dual-st ream injectors with different air mixing mechanisms was carried out ex tensively to understand the spray characteristics of dual-stream port injectors for applications to four-valve gasoline engines. The injecto rs were tested under both steady and transient conditions at different injection pressures and air shrouding pressure differentials. The glo bal spray structure was visualized using the planar laser Mie scatteri ng technique and spray atomization processes were characterized by the phase-Doppler anemometry method. The experimental results showed that spray atomization characteristics are improved markedly by the air-sh rouding technique and also strongly dominated by the air-mixing mechan isms. When the airflows into the injector tip mainly from the radial d irection, two streams of the spray are forced to merge together and as a result a single-stream spray is formed When the radial velocity com ponent of the air is reduced and the air is made to mix well with the fuel inside the injector tip, however, the two streams of the spray ar e well separated over different injection conditions. Moreover, other spray parameters are also modified by the air shrouded into the inject or, which must be optimized in order to achieve the best performance o f the air-shrouded injector.