To Improve High-speed Direct Injection Diesel Engine Combustion Process

This paper consists of two parts. The first part reports the results of investigation to improve performance of a high-speed D.I. Diesel engine by increasing needle valve opening pressure greatly and rate of pumping oil, and meanwhile decreasing intake swirl ratio. Through tests on a single cylinder engine of which bore is 130mm, and stroke 150mm, the experimental results showed that, if the new option ( i.e. needle valve opening pressure is 29 MPa, the pump plunger diameter 12mm and swirl ratio 2.5) was used on the engine, by contrast with old one ( needle valve opening pressure 20 MPa, pump plunger diameter 11mm and swirl ratio 2.9 ), the engine fuel consumption could be reduced and exhaust emissions be improved at high speed, and the engine fuel consumption could be kept on an economical level and exhaust emissions, such as NOx and CO, be decreased at low speed. Moreover, effects of different, needle valve opening pressure, rate of pumping oil and swirl ratio on fuel/air mixing and combustion process were also studied on a model engine and a constant bomb with high pressure by the high speed photography, the laser holography and the technology of laser scattering. Besides, the rate of heat release for combustion process was analyzed with a digital analytical system.The second part of the paper describes an analysis for the impulse of needle valve on needle valve seat in an injector nozzles by the theory of stress wave, and gives formulae to calculate the impulse stress on the valve seat for different types of injector nozzle. These formulae can be used as reliable theoretical bases for designing injector nozzle and selecting adequate needle valve opening pressure.