INFLUENCE MECHANISM OF STAGNATION-POINT FLOW ON LIQUID-PHASE SPRAY PENETRATION LENGTH UNDER ENGINE-LIKE CONDITIONS

Abstract

Formulation of liquid-phase spray penetration length (LPL) is one of the basic research works of direct injection (DI) engines. To predict the spray evolution and LPL in the limited space more accurately, the diffused background-illumination extinction imaging (DBI) technology and highspeed schlieren method were employed to detect the liquid- and vapor-phase spray development in a constant volume combustion chamber (CVCC). The experimental results show that the LPL of the impinging spray is significantly smaller than that of the free spray when the LPL is close to the impinging distance. When the LPL is much smaller than the impinging distance, the LPL of impinging spray is the same as that of free spray. Furthermore, based on the CFD simulation and the stagnation-point flow theory, the spatial distribution of velocity, pressure, and density at the near-wall surface was analyzed in detail. Due to part of the spray kinetic energy was converted into potential energy, creating a sharp increase in pressure and density near the stagnation point, which suppressed the movement of fuel droplets, resulting in a significantly smaller LPL. Moreover, a novel LPL prediction model is introduced, which considering the inhibiting effect of wall on spray penetration and demonstrates enhanced predictive capability of experimental results.