Measurement and Modeling of the Near-Nozzle Ambient Gas Entrainment of High-Pressure Diesel Sprays

The ambient gas entrainment of the diesel spray affects the fuel evaporation and the subsequent ignition and pollutant formation processes. In this work, the gas entrainment process in the breakup length of the diesel spray is investigated by the high-speed micro-particle tracking velocimetry (micro-PTV) technique. With the high frequency of the micro-PTV technique of 28 kHz, the images of the tracer particle and the spray boundary are captured simultaneously in one shot. The experimental results show that during the quasi-steady and transient states, the gas entrainment velocity increases as the injection pressure rises. However, the ambient density has no impact on the entrainment velocity in the breakup length. During the quasi-steady state, the local gas entrainment rate shows a linear dependence on the spray axial distance (z), and the cumulative gas entrainment rate shows a z2 dependence. A theoretical zero-dimensional (0-D) model is proposed to estimate the cumulative gas entrainment rate during the quasi-steady state, and it is validated with the experimental results. The results suggest that the gas entrainment in the breakup length is probably dominated by the breakup process of the liquid core.