Effect And Characteristics Of Shock Waves Induced By High Fuel Injection Pressure

In the fuel injection system of modern diesel engine,increasing the injection pressure is the commonly method used to improve the fuel efficiency and reduce the emission.The appearance of high-pressure common rail system brings that the injection pressure becomes higher and the speed of spray increases.Meanwhile,some advanced combustion technology,such as low temperature combustion and reaction controlled compression ignition,reduces the temperature in cylinder and resulted in a lower local sound velocity,which makes the Mach number of the fuel spray become always higher than 1,and induces the shock waves phenomenon.Shock waves move and develop around the spray.The fluctuation can affect the breakdown of droplets in the spray surface and the diffusion of the mixture in the cylinder,which further affect the atomization characteristics.In order to explore the influence of shock waves phenomenon induced by the spray,experiments of N₂ and SF₆ were carried out in this paper based on schlieren method.Use Matlab image processing function for data processing which could reduce the manual processing data workload.Put forward a kind of image processing based on connected region partition method,this method uses the between-cluster variance method based on linear stretch to get binary image threshold segmentation,after the introduction of the use of the space coordinates image characteristics.Make program software interface based on Matlab GUI function.Understanding shock characteristics is the first step to study shock waves phenomena and their effects.In this paper,the reason of shock waves is analyzed,the variation rule of shock characteristic parameters and the influence of shock wave on spray characteristic are discussed.Shock waves around the spray are mainly divided into leading shock wave and associated waves,they have different causes.The leading shock wave is a result of the orifice exit in the early period of the fuel injection spray forward surface Mach number is higher than1,the associated waves around the spray are the expansion Mach waves.The leading shock waves have two forms,which are oblique shock waves and bow shock waves,and their development are closely related to the forward spray surface Mach number,Mach number for the standard spray forward plane divides the oblique shock wave and the scope of the bow shock wave.The leading shock wave Mach number goes through a process of first increasing and then decreasing with time and finally approaching 1.The shock wave Angle is negatively correlated with the Mach number of forward spray surface.In this paper,the effect of shock wave on spray is described from two aspects of spray macroscopic property and mixing property.At the beginning of the fuel injection,shock wave exists throughout the spray distance is less than the shock does not exist at the time of the spray distance,as time goes past,the shock wave gradually become detached bow shock from the spray,the spray through distance is greater than the shock wave does not exist at this time when throughout the spray distance.At the initial stage of fuel injection,the spray cone angle in the presence of shock waves is larger than that in the absence of shock waves,and the increase rate is about 37.8%.With the development of time,the spray cone Angle in the presence of shock wave tends to be the same as that in the absence of shock wave.The existence of shock wave makes the volume of the spray larger and the effect is more obvious with the increase of injection pressure.Explain the effect of shock waves on fuel atomization.