Abstract
During certain operating conditions in spark-ignited direct injection engines (GDI), the injected fuel will be superheated and begin to rapidly vaporize. Fast vaporization can be beneficial for fuel–oxidizer mixing and subsequent combustion, but it poses the risk of spray collapse. In this work, spray collapse is numerically investigated for a single hole and the spray G eight-hole injector of an engine combustion network (ECN). Results from a new OpenFOAM solver are first compared against results of the commercial CONVERGE software for single-hole injectors and validated. The results corroborate the perception that the superheat ratio Rp, which is typically used for the classification of flashing regimes, cannot describe spray collapse behavior. Three cases using the eight-hole spray G injector geometry are compared with experimental data. The first case is the standard G2 test case, with iso-octane as an injected fluid, which is only slightly superheated, whereas the two other cases use propane and show spray collapse behavior in the experiment. The numerical results support the assumption that the interaction of shocks due to the underexpanded vapor jet causes spray collapse. Further, the spray structures match well with experimental data, and shock interactions that provide an explanation for the observed phenomenon are discussed.
Highlights
Fuel direct injection (GDI) in spark-ignited engines has become a widely used method in the automotive industry to improve engine efficiency and to reduce CO2 emissions
The numerical solver was based on OpenFOAM, and its suitability for predicting injection processes under conditions relevant for direct injection gasoline engines was demonstrated
The solver was validated by the comparison of predictions of fully flashing n-hexane sprays in a single-hole injector with simulations by Guo et al [21], who used the commercial CFD software CONVERGE
Summary
Fuel direct injection (GDI) in spark-ignited engines has become a widely used method in the automotive industry to improve engine efficiency and to reduce CO2 emissions. Similar to underexpanded gaseous jets, a shock system formed outside of the injector, and the authors stated that the interaction of the shocks caused a low-pressure region in the center of the spray, resulting in spray collapse. The same authors investigated the spray collapse of propane using a spray G injector [14] They concluded that spray collapse is caused by the shock interactions of neighboring plumes, which isolate the low-pressure region in the center of the spray from the ambient conditions. The cause of spray collapse due to flashing and the proposed idea of shock interaction for high injection pressures are investigated. Three cases using the spray G configuration are simulated, and plume-to-plume shock interaction is studied
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