Experimental Study On Diesel Spray And Combustion Characteristics Under Low Temperature Condition

Spray and combustion in low temperature is of great significance on start ability, low speed performance and emission performance for the diesel engine. It is of great significance to grasp the influence law and the control strategy of background condition, injection condition and wall condition on the spray and combustion process for the low temperature start of the diesel engine.The gas and liquid spray process image of diesel fuel free jet has been obtained by the shadow method and direct shooting with different injection pressure, different background temperature and density. According to the measurement and calculation, the variation rules of tip penetration, spray angle and spray injection volume for the gas phase and liquid phase were presented. The spray injection volume was divided into two different stages and the parameter analysis method for the spray characteristic has been further concluded. The effect rules of the different experiment condition on the spray characteristic with gas and liquid phase and their difference has been analyzed. The relationship expression between the maximum liquid tip penetration and background condition has been concluded.Then, the combustion process images were taken from high speed camera and dealt with Matlab procedure to analyze the combustion characteristic and obtain the ignition delay period and ignition position which can represent the corresponding ignition characteristic. In the initial combustion stage, the flame intensity characteristic parameter represents the variation rules of flame intensity with combustion time as well as the flame brightness represent the extent of the flame development. Based on the experiment research, the effect rules has been generalized for characteristic parameters of the ignition process and the flame developing process. It has been found that the flame intensity has the dual phase characteristic in the premixed combustion process under low temperature environment.The effect rules of wall height, wall angle and wall temperature on ignition and flame development of diesel free jet has been analyzed by ignition delay period, ignition position distribution and flame intensity characteristic parameter. The wall temperature have obvious effect on the ignition and the flame development of free jet impingement. The lowest ignition temperature of the different background density has been analyzed, and found that it is about 430℃.At last, the maximum compression pressure corresponding to the different rotational speed of the starting process of a diesel engine has been analyzed. The relationship between the ratio of the maximum compression pressure and the adiabatic compression pressure and the engine speed has been fitted, and the expresstion of the maximum compression tempressure has also been analyzed, The control method of the engine speed, the compression ratio, inlet temperature and the fuel supply rate of the flame preheating plug for the engine during the low temperature starting of a diesel engine has been discussed.