【摘要】 基于GDI(gasolinedirectinjection)发动机常用工况点的缸内温度压力,采用高速摄影和纹影法,在高温环境下对比研究了亚/超临界汽油多孔和单孔及异辛烷多孔射流的宏观特性.结果表明:当燃油温度从亚临界态升高至超临界态时,汽油多孔射流在形态上表现出射流中心塌陷和前锋面凸起的特征,异于常见的枝状喷雾结构和剧烈闪沸条件下的坍缩喷雾,同时射流的贯穿距不断增加,锥角不断减小,射流宽度经历了先减小后增大的变化;亚临界汽油单孔射流的贯穿距、锥角及宽度的变化趋势异于汽油多孔射流,表明多孔射流相邻油束间的干涉重叠影响着射流形态结构,在汽油亚临界态时,干涉重叠导致射流轮廓向内收缩,使得射流锥角和宽度减小,而在汽油超临界态时,干涉重叠促进了多孔射流中心的塌陷;相比于单一组分的异辛烷,多组分物蒸发气化的沸点差异是导致汽油射流液相区发生剧烈闪急沸腾,使得射流轴线方向的低压核区发生气流卷吸,并最终诱发射流中心塌陷的原因,而塌陷的发生也使得燃油超临界态时汽油射流宽度大于异辛烷射流宽度;最后,通过对比亚/超临界汽油单孔射流和异辛烷多孔射流,发现导致亚/超临界汽油多孔射流前锋面凸起和中心塌陷的主要原因是射流相邻油束间的干涉重叠及轴线方向低压核区内的气流卷吸作用.更多还原

【Abstract】 Based on the gasoline direct injection(GDI)engine common condition of temperature and pressure incylinder,the high-speed photography and schlieren method were used to compare the macro characteristics of the sub/supercritical states of gasoline multi-hole,single-hole,and isooctane multi-hole jets in high-temperature environments. The results demonstrate that when the fuel temperature rises from the subcritical state to the supercritical state,the center of the gasoline multi-hole jet collapses and shows a morphological protrusion of the front surface.This differs from the typical dendritic spray structure and collapse under severe flashing conditions,during which the penetration of the jet continuously increases,the cone angle continuously decreases,and the jet width first decreases and then increases. The development trends of the penetration,cone angle,and width of the sub-critical gasoline single-hole jets differ from those of the multi-hole jet,which indicates that the interference and overlap of the adjacent plumes affect the jet’s morphological structure. With gasoline in the subcritical state,this interference and overlap cause the jet contour to shrink inward,thereby reducing its cone angle and width,while in the supercritical state of gasoline,the interference and overlap promote the collapse of the contour center of the multi-hole jet. Compared with one-component isooctane,the difference in the boiling point of multi-component vaporization and gasification leads to a sharp flash boiling in the liquid phase of the gasoline jet,causing airflow entrainment in the low-pressure nuclear region in the direction of the jet axis. This contributes to the eventual collapse of the jet center,which then leads to the gasoline jet width being larger than that of the isooctane jet when the fuel is in the supercritical state. Ultimately,the interference of the adjacent plumes and the airflow entrainment of the low-pressure nuclear region in the axial direction are the main reasons for the collapse of the multi-hole jet’s center and the protrusion of the jet front faces of the sub-supercritical gasoline,by contrast with the sub/supercritical gasoline single-hole jet and the isooctane multi-hole jet.更多还原