Study On Characteristic Of Shock Wave Induced By Diesel Spray Based On Schlieren Photography

With the increasingly prominent of the environment issue,emission standard is becoming more and more strict.In order to improve the emission of diesel engine,a variety of techniques such as multiple injection,high pressure injection,exhaust gas recirculation were applied to the combustion in cylinder,the formation of low temperature combustion strategy make the burning path avoid NO_x formation area and carbon smoke generated area.Under the background of new technology,the fuel jet exit velocity is increasing by the improving fuel injection pressure.The weak mixture forming in the process of the pilot injection reduces the local velocity of sound,and efforts to form a low temperature environment inside the cylinder will further reduce the jet around the sound velocity conditions.These factors make the fuel jet exit velocity is higher than the local velocity of sound,resulting in a diesel induced shock wave phenomenon.Nowadays the problem of the supersonic diesel jet induced shock wave have not been thoroughly researched.It is unable to explain from the mechanism of shock wave to the effects of jet atomization,which lead to obstacles in accurately predicting and precise control of the cylinder jet break-up,atomization and the mixture of oil and gas under the condition of the new technology.Therefore,carrying out the research on supersonic jet induced shock wave and its effect on atomization mechanism under similar environment to the in-cylinder of diesel engine has important theoretical significance and engineering application value.According to the experimental phenomena in the open atmosphere,it is pointed out that both the exit of the nozzle and the front surface of the spray are the location of the shock wave.According to the experimental results given back pressure conditions,the structure and the shock wave velocity analysis,confirmed the high back pressure due to decay very quickly the spray speed,shock quickly tends to form circular wave velocity,Maher.It is suggested that the presence of shock waves has a drag effect on the spray front surface,and it plays an important role in promoting the distribution of oil and gas.According to the experimental phenomena of different gas environments,compared with the same injection pressure and ambient density,have no effect on the spray characteristics of the shock wave,the experimental results show that the shock wave promotes the development of spray penetration.Compared with the N₂ condition,the spray penetration under the condition of SF₆ is faster,which may be mainly related to the jet Maher number.