커먼레일 시스템의 비증발 디젤분무에서 분사율과 주변기체의 압력에 따른 주변기체 유입

Abstract

Entrainment of ambient gas is a crucial characteristics of transient diesel spray. recently, it was found that the mass flow rate of ambient gas into transient diesel spray increased with the distance from the nozzle, i.e., axial momentum flow rate of entrained gas increased along spray axis. this tendency is different from the turbulent jet whose momentum flow rate is independent from axial positions. to understand more detailed spray behaviors, it is necessary to quantify the entrainment characteristics of transient diesel sprays under realistic injection and ambient conditions. in this study, measured was the entrained velocity of ambient gas into a diesel spray with LDV(laser doppler velocimetry) technique. non-evaporating transient diesel sprays from a common-rail injection system with triangular injection rate profile wer observed. the effects of ambient gas density and nozzle hole geometry were assessed with entrainment coefficient. there appeared a region where entrainment coefficients were remaining almost contant after onset of entraninment while injection rates wer changing. the effect of common-rail pressure, which altered the slope of injection rate curve, was hardly noticed at this region. entrainment coefficient increased with ambient gas density, that is, the effect of ambient gas density on entrainment of transient diesel spray is larger than that of turbulent jet whose entrainment coefficient remains constant. non-dimensional distance was defined to reflect the effect of nozzle hole diameter and ambient gas density together. mean value of entrainment coefficient was found to increase with non-dimensional distance from the nozzle