An Experimental Study Of Flash Boiling And Supercritical DME Spray Characteristics

To further improve the diesel engine power,economy and emissions is the main direction of development of diesel engines in the future.The use of high-intensity combustion technology is an important way to achieve the above requirements,so the rapid preparation of the mixture put forward higher requirements.Flash boiling spray and supercritical injection in the preparation of mixed gas has great advantage.Dimethyl ether is an ideal diesel fuels alternative,with better fire performance,and can effectively reduce pollutant emissions.Due to the relatively low boiling point and the critical temperature of dimethyl ether,it is easier to achieve flash boiling spray and supercritical injection in the injection process.Therefore,it is very important to study the influencing factors of dimethyl ether flash boiling spray and supercritical spray.In this paper,the basic physical parameters of DME are used to analyze the applicable range of the current gas equation of state.The DME equation of state under high temperature and high pressure is proposed.By comparing with the data from the National Institute of Standards and Technology,it is found that the calculation accuracy is obviously improved in the range of temperature(450K ～ 750K)and pressure(6MPa ～ 25MPa).the temperature is700 K,with the pressure changes,the error can be maintained within 0.5%.In this paper,we set up a constant volume device,re-set up the DME fuel injection system,adding heating device in the fuel pipeline,the use of high-speed camera and shadow instrument to achieve the optical and shadow of the optical test methods to obtain DME vapor and liquid phase Image,and write Matlab program to spray photos for image processing,access to the spray through distance and spray width and other information to improve the experimental image processing efficiency.The experimental results show that with the decrease of ambient pressure,the penetration of flash boiling liquid phase spray gradually increases,and a sudden change occurs at 0.1 MPa.Ambient pressure is in the range of 1.1MPa to 0.3MPa.The tendency of dimethyl ether supercritical liquid phase spray through spray distance is opposite to that of flash boiling liquid phase spray.With the decrease of ambient pressure,the penetration distance of dimethyl ether supercritical liquid phase spray decreases.With the increase of fuel temperature,there was no obvious change in the shape of gas spray,and the penetration distance gradually decreased.