Several mechanisms are available for the multi-jet GDI spray collapse under low ambient pressure (≤ 1.0 bar) flash-boiling (LP-FB) and non-flash-boiling (NFB) conditions. The present investigation is to clarify the applicability of the available mechanisms under different thermodynamic states. The tests were carried out in an optically accessible constant volume vessel using a two-hole GDI injector over fuel temperature (T_fuel) ranging from 50° to 130°C and ambient pressure (P_amb) ranging from 0.2 to 9.0 bar. The collapse could be found both under LP-FB and NFB conditions, but their characteristics changing with P_amb and T_fuel showed the opposite trends. The LP-FB collapse enhanced as P_amb decreased or T_fuel increased while the NFB collapse weakened as P_amb decreased and could disappear once Tfuel was beyond 70°C. Further analysis into the temporal spray development showed that the LP-FB collapse occurred at the very beginning of injection accompanied with the occurrence of a new jet between the original jets (termed as "inter-jet jet") while the NFB collapse gradually occurred with the time elapsed. The NFB collapse was attributed to the low-pressure zone caused by the jet entrainment. The disappearance of NFB collapse as T_fuel increased demonstrated that the enhanced evaporation would counteract this low-pressure zone. This also provided the strong support that the LP-FB collapse could not be induced by the jet entrainment because the flashing evaporation was much stronger. After careful examination of the available mechanisms, it was more likely that the occurrence of under-expansion in LP-FB jets and their interactions at the nozzle exit caused the collapse.

中文翻译：

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两孔GDI注射器闪沸与非闪沸条件下塌陷模式的对比研究

有多种机制可用于低环境压力 (≤ 1.0 bar) 闪蒸 (LP-FB) 和非闪蒸沸腾 (NFB) 条件下的多喷嘴 GDI 喷雾塌陷。目前的研究是为了阐明现有机制在不同热力学状态下的适用性。测试是在光学可访问的定容容器中使用两孔 GDI 喷射器在 50° 至 130°C 的燃料温度 (T _Fuel ) 和0.2 至 9.0 bar 的环境压力 (P _{amb ) 范围内进行的。}在LP-FB和NFB条件下都可以发现塌陷，但它们的特性随P _amb和T_燃料的变化呈现出相反的趋势。LP-FB 塌陷随着 P _amb降低或 T_Fuel增加，而 NFB 崩溃随着 P _amb减少而减弱，一旦 Tfuel 超过 70°C，NFB 崩溃就会消失。对时间喷雾发展的进一步分析表明，LP-FB塌陷发生在喷射一开始，伴随着原始射流之间出现新的射流（称为“射流间射流”），而NFB塌陷则逐渐发生时间过去了。NFB 塌陷归因于射流夹带造成的低压区。_{NFB崩溃作为T燃料}的消失增加表明蒸发的增强会抵消该低压区。这也有力地支持了LP-FB塌陷不能由射流夹带引起，因为闪蒸更强。在仔细检查可用机制后，更有可能的是 LP-FB 射流发生膨胀不足及其在喷嘴出口处的相互作用导致了塌陷。