Experimental And Numerical Reserch On Spray And Atomization Of N-decane Under Supercritical Condition

Under the working condition of aviation engine,the cylinder is enrich of ambient mixture of high temperature and high pressure,which are usually higher than the critical points of the fuels.Then the fuel under supercritical condition will show some special characteristics.For analyzing the spray and atomization of fuels under supercritical in-cylinder condition,it is necessary to investigate the difference between the spray characteristics under supercritical condition and conventional condition.The components and their proportions of aviation fuel,as a mixture refined from the oil fuel,are complex.It is necessary to build up a surrogate which contains only a few kinds of fuels and keeps consistent in characteristics with the original aviation fuel.N-decane,which has a similar C number in the molecular as the aviation fuel components,are usually used to be a component of the aviation surrogate fuels,so the research of the characteristics of n-decane is of great importance.This paper contains the establishment of the measurement platform of spray under supercritical condition.Mie scattering and Schlieren were used to measure the spray characteristics,such as liquid penetration,spray penetration and spray cone angle.The shape of spray was analyzed to investigate the influence of the ambient condition on the spray.Some relative measurement experiments were designed to estimate the critical point of n-decane so as to establish a supercritical ambient condition in the constant volume chamber for the following spray measurement.Mie scattering and Schlieren were used to measure the spray images and a MATLAB algorithm was developed for image dealing to extract the spray characteristcs.Analyzed the influence of temperature on the n-decane spray characteristics.The result shows that the rising of temperature promotes the phase change between liquid and supercritical phase of the spray,while the changes of spray penetration and cone angle are minimal,which is the special phenomenon of the spray under supercritical condition.To establish the simulation model of the spray and atomization under supercritical condition,the CFD code CONVERGE was used to analyze the effect of mesh refinement,the spray model KH-ACT and the sub-grid turbulence model STD on the spray characteristics.The result shows that when the minimize grid scale is 0.03125 mm,the simulation result is basically the same as the experimental result.The KH-ACT model,which is aimed to modify the KH model with the effect of cavitation and turbulence induced droplet breakup,can promote the primary breakup of the spray and make the results more accurate.STD model is used to modify the sub-grid turbulence by the stochastic turbulence dispersion,which can lead to a reasonable result when the turbulence dispersion coefficient equals to 0.16.Finally,a simulation model for spray under supercritical condition was established and come to an accurate result of the spray characteristics.The research of fuels under supercritical condition needs further promotion and the establishment of the simulation model for n-decane spray acts as a foundation for further research on aviation surrogate fuel.The following research will aim at the establishment of aviation surrogate fuel and predict the spray and atomization.The final intent is to provide a method to promote the atomization,accelerate the mixing of fuel and ambient air and improve the combustion and push the development of energy conservation and emission reduction.