Nozzle Tip Wetting in GDI Injector and Its Link with Nozzle Spray Hole Length 2022-01-0498

Fuel film deposited on fuel injector tips used in gasoline direct injection engines, otherwise known as nozzle tip wetting, has been identified as an essential source of particle emissions. Attempts have been made to reduce nozzle tip wetting by the optimization design of nozzle geometry parameters. However, relevant investigations are still limited to emission measurements and corresponding indirect analysis. Due to the lack of related visualization research, the mechanism of nozzle tip wetting formation and its link with nozzle internal flow are still unclear. To clarify the influence of spray hole length on nozzle tip wetting and the underlying mechanisms, the dynamic formation process and the fuel film area evolution of nozzle tip wetting were visualized directly using laser-induced fluorescence technique and photomicrography technique. The investigation was carried out in a constant volume chamber, using injectors of different spray hole lengths, under sub-cooled conditions and flash boiling conditions. It was found that with an increase in spray hole length, the nozzle tip wetting decreased under sub-cooled conditions and increased under flash boiling conditions. A further study was conducted to examine the effect of spray hole length on fuel film evaporation. The results showed that with an increase of spray hole length, the evaporation under sub-cooled conditions increased monotonously and an opposite trend was obtained under flash boiling conditions. The phenomena aforementioned can be well understood with the theory of phase change inside the nozzle and atomization outside the nozzle, which can contribute to the control strategies of nozzle tip wetting and the optimization design of fuel injection systems.