A Micro-Variable Circular Orifice Fuel Injector for HCCI-Conventional Engine Combustion - Part I Numerical Simulation of Cavitation

The cavitation flow characteristics inside the micro-variable circular orifice (MVCO) fuel injector have been investigated through numerical simulations. The results show that cavitation inside the conical nozzle significantly influences the conical spray characteristics. The spray velocity loss is increased through the choked cavitation flow, and liquid spray angle and drop size is reduced by cavitation. A cavitation map has been generated by dividing the operating conditions into four regimes featuring full cavitation, partial cavitation at outlet, partial cavitation at inlet, and no cavitation respectively according to the area of cavitation inside the nozzle. We found that, in order to be in full cavitation regime, an inlet pressure at 500 bar is sufficient when the outlet pressure is less than 30 bar, where the liquid fuel can be easily atomized; however, when the outlet pressure exceeds 30 bar, the required inlet pressure jumps to 2200 bar. The effects of fuel properties and conical outlet geometries have also been studied.