개변압에 따른 디젤 분무의 분사말기 미립화 특성

Abstract

In conventional diesel fuel injection systems, theoretically, the closing pressure for the needle valve is lower than opening pressure since the areas to which the hydraulic pressure applies are designed to be different. And in practice, the closing pressure appears to be even lower than the thoretical value due to mechanical friction between the needle and the nozzle body and also due to the inertia of the needle itself. Therefore, atomization performance appears to be poor especially at the final stage of injection. One way to overcome this problem is to set the opening pressure of the needle valve to the higher value by adjusting the valve spring and accordingly, the closing pressure would increase. In the present study, a series of experiments have been performed to examine the atomization characteristics at the final stage of injection with the change of the opening(closing) and the back pressures using photographic method. The atomization performance at the final stage was not prominently improved when the opening pressure is increased due to the after-injection of the fuel(by bouncing of the needle) and also due to the dripping of the remaining fuel within the sac volume.