Stability Analysis Of Supercritical Spray Of Circular Jet

The fluid in the supercritical state has distinctly different attributes from the subcritical state.In the supercritical state,the interface between the liquid and the gas has ceased to exist,the liquid surface tension and latent heat of the vapor tend to zero,so there is no longer the distinction between liquid and gas,but can only be collectively referred to as supercritical fluid.The fragmentation mechanism of circular jet in supercritical state is very different from that of subcritical circular jet.The mixing process of supercritical fuel will occupy an important position in the future focus on the field of internal combustion engine research.Therefore,the study of the fragmentation process of supercritical circular jet is an important part of engine spray research.At present,the theory of linear stability of circular jet fragmentation process is mostly adopted.The core and key point of this theory lies in the derivation of dispersion relation.Because the derivation of dispersion relation needs to have solid fluid mechanics and mathematical knowledge,and the process of derivation is very complicated,it is often necessary to study repeatedly to make progress.The fragmentation and atomization of circular jet is very important for the scientific research of engine spray and combustion.The theory of linear stability is an important method to study the process of liquid fragmentation.In this paper,the stability of circular jet supercritical spray was studied.The main research process and conclusions are as follows:（1）According to the established three-zone physical model of viscous circular jet entering the atomization process in incompressible gas medium under supercritical environmental conditions,based on the linear continuity equation and the momentum equation,a dimensionally linearized Navier-Stokes（N-S）equation was established.After the dimensioning process,the dimension-N-S criterion control equation is obtained.According to the difference of the medium,it was divided into three parts: liquid phase,mixed gas phase and air phase zone.Finally,the dispersion criterion relation and the stability limit were obtained at the interface between the liquid phase and the mixed gas and the interface between the mixed gas phase and the air.（2）Performed the input parameter setting of the numerical calculation.Using the L-Kequation of the actual gas,the FORTRAN language calculation program was compiled and the input parameters of the supercritical air environment were calculated theoretically.Then the numerical calculation parameters of the fixed bomb and the diesel engine were obtained.（3）Using the cylindrical jet model calculation program of Sister Li Yanxia to replace the input parameters of the diesel engine spray,the calculation precision is TOL=1.7×10^-5,the liquid fuel jet fragmentation numerical calculation was carried out.The growth phase of the surface wave amplitude calculated from the zero-order perturbation amplitude had （?） tewx in less than one wave（the first calculated data point）,Indicating that the disturbance amplitude of the cylindrical surface of the liquid fuel has crossed the middle axis,Liquid fuel was immediately broken when When coming out of the nozzle.While the supercritical spray model of the diesel engine surface wave is a mixture of gas,So that the amplitude of the disturbance of the surface wave can only show that the mixture is mixed with each other even if it crosses the intermediate axis.（4）Set the calculation accuracy of one ten thousandth to carry out theoretical calculations.Using the calculated maximum surface wave growth rate,spray radius,penetration distance and the spray cone angle at the three injection times t₁=0.61ms,t₂=1.05ms,t₃=1.49ms,when n = 0,the internal pressure of the fixed bomb was 800 K,and the back pressure was 3.39 MPa,comparing with corresponding experimental data,the three-time spray profiles calculated by the theoretical calculation were compared with the image taken by spray experiment and the error analysis was carried out.So got the conclusion:If the initial disturbance amplitude is estimated at the first moment as the basis,the longer the spray time was,the greater the error of the spray oil beam radius between the theoretical calculation value and the experimental data was,the smaller the error of through distance between the theoretical calculation value and the experimental data was,and the smaller the error of the spray cone angle between the theoretical calculation value and the experimental data.Theoretical calculation and experimental data error is less than double,the two are basically consistent.The difference between theoretical and experimental results may be due to the fact that our current theoretical model is based on the analysis of linear stability and does not take into account the effect that the velocity of the sprayed oil is attenuated by the blocking effect of the ambient gas.At the nozzle outlet,the jetting speed is large,and the degree of attenuation is larger by the blocking effect of the ambient gas.The farther away from the nozzle,the smaller the oil velocity,the less the decay of the velocity value,the closer the theoretical calculation is to the experiment data.The use of nonlinear stability theory will make the numerical calculation of the higher accuracy.On the whole,in this paper,the linear stability of viscous compressible supercritical fluid injection into non-viscous incompressible air environment has been analyzed.Based on the comparison between the theoretical calculation results and the experimental results,we establish the supercritical spray linear stability of diesel engine The theoretical model is a useful attempt and discussion,which plays a guiding role in the study of supercritical spray process of internal combustion engine hole nozzle.