ID 337

The effects of flash boiling on near-nozzle behavior of a gasoline direct injector during transient needle motion

 

Abstract:

The early and late portions of transient fuel injection have proven to be a rich area of research, especially since the end of injection can cause a disproportionate amount of emissions in direct injection internal combustion engines. While simulating the internal flow of fuel injectors, valve opening and closing events are the perennial challenge. A typical adaptive-mesh CFD simulation is extremely computationally expensive, as the small gap between the needle valve and the seat requires very small cells to be resolved properly. Capturing complete closure usually involves a topological change in the computational domain. The presented work simulates a gasoline direct injector operating under cavitating conditions by employing a more gradual and easily implemented model of closure that avoids spurious water-hammer effects. The results show cavitation at low valve lift for both flash boiling and non-flash boiling conditions. Further, this study reveals post-closure dynamics that result in dribble, which is expected to contribute to unburnt hydrocarbon emissions. Flashing versus non-flashing conditions is shown to cause different SAC and nozzle behavior after needle closure. In particular, a slowly boiling SAC causes spurious injection behavior. Differences in the injector tip wetting process between flashing and non-flashing conditions are also observed.