ID 204

Injector tip wetting evaluation with different nozzle outlet configurations

 

Abstract:

Recently, fuel wetted area on the surface of injector tip after fuel injection in gasoline direct injection engine is attracting attention. Residual fuel on the injector tip could be a huge source of PN emission due to diffusion combustion. In this research, fuel wetted area on the surface of the GDI injector tip after fuel injection was evaluated in a spray chamber. Wetted area was captured with laser induced fluorescence technique. First, injector tip was magnified with long distance microscope. Second, at 1.3 ms after fuel injection, 266 nm Nd:Yag laser pulse shot was used as excitation light source. Lastly, the fluorescence light signal was captured with intensified charge coupled device camera with optical band pass filter. Fuel temperature, injection pressure, ambient temperature, ambient pressure were controlled with lab made in-house system. Simulated in-cylinder conditions were 4, 10 and 14 bar Brake mean effective pressure under cold and hot fuel temperature. In order to find out the reason of the wetted area, microscopic backlight imaging technique was used. Near nozzle spray angle and width were evaluated. For further understanding, nozzle outlet step-hole configuration was changed. Step-hole diameter and length were changed and tip wetted area and near nozzle spray angle and width were measured. The result showed smaller diameter and short length step-hole case showed less fuel wetted area. Spray and step-hole outlet interaction, air vortices intensity inside of the step-hole and fuel momentum loss under transient needle operation conditions were thought to have impact on injector tip wetting.