Effect Of Ambient Pressure And Thermal Environment On Single Droplet Evaporation

The evaporation of fuel droplets is an important process in the combustion of liquid fuel. Lots of experiments have shown that most of the combustion phenomena of liquid fuel are diffusion-governed, in which the combustion rate is large but the evaporation rate is small. The evaporation rate of the droplets has significant influence on the combustion and the performance of those equipments. Thus, the investigation on the evaporation characteristics of a single droplet is of important value.The droplet evaporation is a coupled physical phenomenon involving heattransfer, mass transport and gas flow. Being influenced by many factors, its mechanism and characteristics are quite complex. In recent decades, many scholars have contributed to the evaporation models and the characteristics of single droplet. But the knowledge on droplet evaporation is still absent.On the basis of anterior study, the evaporation characteristics of a single droplet of hydrocarbon are analyzed by numerical modeling in this thesis. The researches mainly include three problems as following:(1) A numerical modeling program for the isothermal droplet evaporation in convective thermal environment was developed with considering the dependency of the physical properties of gas mixture and fuel liquid on thermal environment and ambient pressure. With the reliability being verified, the influences of ambient pressure on the isothermal droplet evaporation in different convective thermal environments were analyzed and the transition temperature zones of pressure effects were obtained.(2) The one dimensional transient evaporation model for a single non-isothermal droplet with thermal conduction inside was introduced, and the variable physical properties of gas mixture and fuel liquid were considered. The numerical method and calculating code were developed and verified. The transient evaporation of a single non-isothermal droplet was simulated to analyze the effects of ambient pressure and convective thermal environment. A comparison with the evaporation of isothermal droplet was conducted and the transition temperature zones of pressure effects on the evaporation of a single non-isothermal droplet were obtained.(3) On the research basis of non-isothermal droplet evaporation, an evaporation model including the thermal radiation absorption of droplet was presented. And the effects of ambient thermal radiation on droplet evaporation were analyzed preliminarily.From the investigation, the quantitative effects of ambient pressure, environment temperature, convective intensity and thermal radiation on the evaporation of a single fuel droplet have been obtained. Some valuable conclusions were drawn by analyzing the inside thermal conduction and swelling effect of droplet in the transient heated stage. And those will be helpful to the further research on droplet evaporation.