Abstract
In a direct injection diesel engine, combustion characteristics are greatly influenced by the mixture formation behavior of diesel spray. This behavior depends on various conditions such as nozzle geometry, injection pressure and ambient gas density. Recently, boost pressure of a diesel engine is set to increase in order to meet downsizing of the engine. Consequently, compressed air density in the cylinder is becoming high as compared with the density of a conventional diesel engine, and it seems that the compressed air density affects more strongly the mixing process of diesel spray. Therefore, under high ambient gas condition, it is necessary to understand precise spray behavior in terms of velocity distribution inside a diesel spray. In this study, time-resolved particle image velocimetry (PIV) was applied to sequential images of diesel spray in order to assess velocity distribution inside the spray in high density gas surroundings. As the results obtained, it was clear that spray width increased with increasing ambient gas density and injection pressure. PIV analysis shows the detail velocity distribution inside the spray. Ambient gas density effect on the spray width was larger than injection pressure effect. Moreover, local position of intense mixing zone shifted from spray periphery to inside a spray with an increase of ambient gas density and injection pressure.
