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In this study, the spray characteristics of a five-hole gasoline direct injector were investigated in a constant volume vessel. The absolute ambient pressure ranged from 0.5 to 10.0 bar, and the fuel temperatures were 20 °C and 80 °C. High-speed imaging and phase Doppler measurement technique were utilized to investigate the spray morphology and the droplet dynamics, respectively. Spray collapses were observed in the near field under the elevated ambient pressure (higher than 1.0 bar) conditions and in the far field under the flash boiling conditions in both macroscopic and microscopic levels. In addition, under the elevated ambient pressure conditions, the droplets at the inner side of the target jet were larger than those at the outer side, due to the increased probability of droplet coalescence as a result of spray collapse. Whilst, slight increase in droplet diameter in the inner side of the target jet was also found under the flash boiling conditions. Furthermore, the near-field collapse at the elevated ambient pressure conditions was attributed to the jet-air interaction, termed as jet-induced spray collapse; and the far-field collapse under the flash boiling conditions was attributed to the dramatic temperature drop and the resultant vapor condensation, termed as condensation-induced spray collapse. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Spray collapse of the ECN Spray G injector was studied under flashing conditions. • The flow development of flashing sprays was strongly tied with the fuel properties. • With propane, the flow was transonic and a unique shock structure was formed. • The underlying physics of the spray collapse process was discussed in detail. This work features a numerical study of the spray collapse process that occurs under flash-boiling, gasoline-direct-injection conditions. The Engine Combustion Network's Spray G injector was modeled, and iso-octane, n-hexane, and propane were used as fuels with the goal to investigate fuel property effects. The development of individual jets and jet-to-jet interaction were analyzed to reveal the physical mechanisms of spray collapse. The results agreed qualitatively well with the experimental data of propane available from the literature and the predictions revealed the model's ability to capture the near-nozzle shock structures witnessed in the experiments. Simulations showed that the flow development of flashing sprays was strongly tied with the fuel properties. Specifically, under-expanded jets were not observed with iso-octane due to the fuel's low vapor pressure. In the case of n-hexane, the jets were under-expanded, and a low-pressure core was observed inside the jets due to the flow expansion. With propane, the very strong expansion caused the flow to become transonic and generate a unique shock structure near the nozzle exit. The shock structure revealed the formation of primary shock cells within the jets and secondary shock cells induced by jet-to-jet interaction. Based on the results, the spray collapse under flash boiling conditions was mainly attributed to two effects, i.e., the decrease in pressure at the spray center induced by the low-pressure cores inside and between the jets, and the isolation effect due to the jet-to-jet interaction which contributed to maintain the pressure differential between the spray center and the ambient. [ABSTRACT FROM AUTHOR]

Microscopic and macroscopic impingement characteristics of a single jet were investigated under various flash boiling conditions. The influences of split injection strategy and the related interaction between split injections were studied. The fuel concentration distribution during the impingement process was also quantified. It was found that non-flash boiling condition lead to large secondary droplets and ligaments, resulting in a large amount of liquid fuel deposited on the impact surface. The boosted flash boiling could effectively reduce the sizes of primary droplets and secondary droplets and the resultant deposited fuel. The employment of split injection strategy could further decrease the deposited fuel. The second split injection built up the fuel film more quickly than the first injection due to the existence of the built fuel film by the first injection, however, increasing flash boiling strength decreased the building-up rate by improving dispersion and evaporation. In addition, the concentration of the deposited fuel on the surface could effectively be reduced by enhanced flash boiling and the lifetime of dense fuel was shortened by increasing dwell interval between split injections. [ABSTRACT FROM AUTHOR]