IMPACT OF ENLARGED SCALES AND CONTINUOUS BUBBLES ON CAVITATION PATTERNS OF DIESEL NOZZLES

Abstract

Spray developments are mostly influenced by the flow characteristics inside a diesel nozzle orifice. In this paper, an experimental visual system is built with transparent nozzles. This test rig is used to explore the effect of enlarged scales and continuous bubbles on the cavitation phenomena in CI nozzles. The variation of discharge coefficient with the cavitation number under two cavitation patterns and the scale effect of string cavitation on the discharge coefficient under three enlarged scales are also explored. Additionally, the spatial distribution of standard deviations with two cavitation patterns is compared and analyzed. Under different enlarged scales, the results indicate that the development stages of string cavitation with two-phase flow are almost the same, having similar behaviors through the transitional period from single-phase flow to cavitation fully developed flow. Compared to the situation without bubbles, the cavitation intensity and spray cone angle are promoted. Furthermore, the effect of continuous bubbles is studied under the single-injection working condition, and the results illustrate that string cavitation is very sensitive to the bubble content. The finding also reveals that continuous bubbles lead to an enhancement in the string cavitation inception compared to that in the geometry-induced cavitation under the same conditions.