Experimental And Numerical Study On Vaporization Of Bi-component Fuel Droplets

The multi-component evaporation model commonly used in engineering practice cannot effectively describe the boiling phenomenon of mixed fuel droplets with large difference in boiling points in the vaporization process under high-temperature conditions in combustion chamber of internal combustion engine.For improving the fuel droplet vaporization process numerical simulation precision to increase the applicability of the droplet vaporization model of mixed fuel,in this paper,the bi-component fuel droplet of n-butanol/n-hexadecane had be taken as the research object,and its vaporization characteristics under high-temperature environment were studied experimentally.The two-component droplet vaporization model was established,and the reliability of the model was verified.The specific work is as follows:(1)The vaporization characteristics of two-component droplets with different boiling points at high temperature were studied.The vaporization of n-butanol and n-hexadecane and their mixed droplets in the high-temperature heating environment was studied experimentally.The results showed that the vaporization of n-butanol/n-hexadecane mixture under high-temperature conditions could be divided into three stages: initial evaporation stage,boiling stage and later evaporation stage.The first two stages were controlled by vaporization of lighter component n-butanol,and the last stage was controlled by vaporization of heavier component n-hexadecane.(2)It is found that increasing the ambient temperature could effectively reduce the lifetime of droplets and accelerate the average evaporation rate of droplets.The rise of ambient temperature could also accelerate the growth rate of bubbles in the droplet and increase the intensity of boiling.Under the high-temperature environment,the component ratio of the droplet had a great influence on the vaporization characteristics of the droplet.The experiment found that under the high temperature environment,the average vaporization rate of 20% n-butanol/n-hexadecane droplet was faster than that of the 40% mixture droplet due to the influence of boiling and other factors.(3)A bi-component droplet boiling vaporization model was developed based on the phenomenon that bubbles were generated by the large difference of boiling point in the bi-component droplet at high temperature.In this model,the mass boiling vaporization rate of droplets was proposed,and the bubble point temperature of the blended droplets was employed to evaluate the start/stop moment of boiling.By comparing the boiling model with the evaporation model,it could be seen that the boiling model can better predict the droplet life for different ambient temperatures.As the ambient temperature increases,the prediction error of the evaporation model on the droplet lifetime decreases,but the effect on the vaporization trend is not as good as the boiling model.The boiling rate has a great influence on the simulation of the vaporization process.For the prediction of the vaporization process of the bi-component droplets with large difference in boiling point,the boiling model is more accurate.Two boiling criteria are compared: the bubble point of the mixture and the boiling point of the volatile component.The criterion for boiling with bubble point is more accurate than the criterion for boiling point of volatile component.As the ambient temperature increases,the deviation of the boiling point criterion gradually decreases.