Nozzles in fuel injectors for direct injection gasoline engines are exposed to high temperature combustion gases and soot. In such rigorous environment, it is feared that the decrease in fuel flow rate and the change in spray shape in the injector are caused by deposit accumulation on the nozzle. Fundamental factors of nozzle deposit formation in the nozzle hole were investigated through injector bench tests and engine dynamometer tests, and deposit accumulation processes were observed by scanning electron microscope. The investigation results reveal the nozzle deposit formation mechanism and the way how to suppress the deposit in the nozzle hole. In order to suppress the deposit in the nozzle hole, the nozzle temperature is required to be lower than the 90% distillation temperature of the fuel. In such a state, the residual fuel in the nozzle hole is maintained to be in a liquid state, and the deposit precursors are easily washed away with a fuel injection, so that the deposit formation is restrained in the nozzle hole.
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