Droplet dynamics of DI spray from sub-atmospheric to elevated ambient pressure

• Time-resolved development of droplet velocity during spray process was described.
• Bifurcation of jet was observed at sub-atmospheric and atmospheric pressure.
• The modes of droplet velocity distribution are determined by the ambient pressure.
• Increase in injection pressure advances and enhances the deviation of jet.

In this study, one of the five jets issued from a 5-hole Direct Injection (DI) injector was studied in detail using Phase Doppler Particle Analyzer (PDPA) and high speed imaging techniques. The tests were carried out in a constant volume vessel with absolute ambient pressures ranging from 0.05 to 0.5 MPa and injection pressures ranging from 6.0 to 15.0 MPa. Throughout the test conditions, the jet trajectory deviation of the target jet is observed due to the gas pressure imbalance between the inner and outer sides of the target jet. Both the results from spray morphology and the time-resolved droplet velocity have demonstrated the bifurcation of the target jet during the spray process at sub-atmospheric and atmospheric ambient pressures. It is attributed to the joint effects of the pressure imbalance between the two sides of the target jet and the velocity distribution change at the nozzle exit which relates to the vapor pressure of gasoline. The increase in injection pressure advances and enhances the deviation of the jet trajectory due to the larger jet speed. The deviation and/or bifurcation of the target jet also changed the size distribution.