EXPERIMENTAL INVESTIGATION OF SPRAY CHARACTERISTICS OF MULTI-HOLE AND SLOT GDI INJECTORS AT VARIOUS FUEL TEMPERATURES USING CLOSELY SPACED SPLIT-INJECTION STRATEGIES

摘要

In this study, multi-hole and slot gasoline direct-injection (GDI) injectors were investigated at various fuel temperatures by using various closely spaced split-injection strategies. The four tested injectors were a six-hole injector, a four-slot injector, a three-slot injector, and a one-slot injector. N-heptane was chosen as the test fuel, and fuel temperature ranged from 25 degrees C to 130 degrees C. Various closely coupled split-injection strategies were investigated, including single injection, double injection, triple injection, and quadruple injection. Results showed that fuel temperature had a negligible effect on global spray structure when fuel vapor pressure was lower than the ambient pressure, and spray structure was mainly dominated by injector configuration. Spray collapse occurred at strong superheated conditions of all injectors, which altered spray structure and, consequently, the fuel distribution. However, different trends of spray penetration caused by spray collapse were observed. Strong spray collapse led to increased spray penetration of the six-hole injector; but for the slot injectors, spray penetration was smaller than that at cold fuel temperature even when strong spray collapse occurred. By using quadruple-injection strategy, penetration of strong collapsed fuel spray was even shorter than that of fuel spray at 25 degrees C fuel temperature of single injection of the six-hole injector. Finally, it can be concluded that by using special injector configuration or split-injection strategy, the overpenetrating issue caused by strong spray collapse at high fuel temperatures of multi-hole GDI injectors can be mitigated or avoided.