Numerical Simulation And Expefiment Study Of Heat And Mass Transfer Mechanisms Of Fuel Droplet Evaporation

The process of fuel spray, atomization, evaporation and combustion is very important to the direct inject diesel engine. The fuel evaporation process and spatial distribution largely determines the characteristics of the diesel combustion process. Therefore, it is necessary to carry out the study of the heat and mass transfer mechanism of fuel droplet evaporation process in direct injection diesel engine. Based on the fuel droplet evaporation in direct injection diesel engine, the study of heat and mass transfer mechanism of droplet evaporation was carried out using numerical simulation, theoretical analysis and experimental methods.Due to the limitations of experimental conditions and method of numerical simulation, the current understanding of the heat and mass transfer mechanism of fuel droplet evaporation process is not perfect. The researcher used the empirical formula to study droplet evaporation for engineering applications. However, the existing empirical formula can not accurately simulate the droplet evaporation process and experimental conditions can not be observed in the distribution of droplet internal flow field. The methods of separate gas and liquid phase modeling are widely used in numerical simulation of droplet evaporation process. It is necessary to adopt a numerical simulation method of gas-liquid two-phase flow of fuel droplet heat and mass transfer.The mathematical model of fuel droplet evaporation process based on large eddy simulation VOF method of gas-liquid two-phase flow is established. This model can describe the gas-liquid two-phase flow field, the temperature gradient, the concentration gradient and the deformation of fuel droplets. Formula based on Fick’s law of diffusion concentration gradient principle, be applied to the numerical simulation of fuel droplet evaporation process. The numerical simulation of the fuel droplet evaporation process will be introduced by the Marangoni effect caused by surface tension gradient in the phase boundary. The Marangoni effect is simplified to the volumn force, which considers the effect of the temperature. The effect of the heat and mass transfer mechanism of fuel droplet evaporation process caused by Marangoni effect is studied.The fuel droplet evaporation process is influenced by the role of environmental factors in the temperature, pressure and turbulence in direct injection diesel engine. For in-depth understanding of the heat and mass transfer mechanism of the fuel droplet evaporation process, the various environmental factors on the liquid phase heat transfer and gas-liquid phase mass transfer is studied.Existing fuel droplet evaporation rate model widely used in the correlation calculation in the droplet evaporation, such as spray combustion applications. This model is assumed that the droplets always maintain the shape of the ball, and therefore the correlation calculation of the area or volume is obtained in accordance with the formula of the sphere. For practical terms, the shape of fuel droplets in the evaporation process continues changing. By analyzing the obtained variation of the surface area and the key factors affecting droplet deformation, the formula of droplet surface area is obtained by regression analysis, and fuel droplet evaporation rate model was successfully corrected. For the entire compute cycles, the results of the modified model are closer to the experimental value than that of the original model. This shows that droplet deformation correction model can accurately predict the experimental values.Through the analysis of the distribution of the fuel droplets in the field of diesel spray, the effect of different droplet number array and the droplet spacing on heat and mass transfer are studied. The Nusselt number of the droplet array is improved.The improved Nusselt number of the droplet array is validated.The high-temperature environment experimental system based on temperature closed-loop controlled is established. A systematic analysis of the fuel droplets evaporation characteristics of the different components with the environmental temperature changing is carried out. The fuel droplet evaporation characteristic of different components is also carried out. The numerical model is validated by the experimental results of fuel droplet evaporation.