Numerical Simulation Of Convection And Radiation Combined Heat Transfer And Study Of The In-cylinder Radiation Heat Transfer

Since the end of the last century,the development of computer technology has made great progress,recently,the field of diesel engines relies on computational fluid dynamics(CFD)more heavily.Numerical simulation can provide the details of the flow and heat transfer which the experiments is difficult to handle.It is of great significance in design process of engine as well as in performance test and optimization.The key of the numerical simulation of radiation heat transfer in cylinder of diesel engine include the solving of radiative transfer equation,coupled flow and radiation and calculating physical properties of CO2 and H2O in high-temperature.At present,relatively few studies are of awareness for radiative heat transfer of in-cylinder.Based on the self-developed computational multi-physical software GTEA,radiation module on the basis of cell-centered finite volume method has been added to the software,achieving the coupling calculation of flow and radiation and simulating the radiation heat transfer of in-cylinder.The main contents are as follows:(1)Accomplish the computational program of the radiation transfer equation.For absorbing,emiting,isotropic scattering medium,radiative transfer equation is discretized with the use of FVM.The computational procedure is built by Fortran programming language.The flow field meshes could also be used to solve radiation filed,which provides much convenience and generality for the program.When the number of the grids and discrete of solid angles satisfy certain relationships,the simulation can get more accurate results.When the wall boundary condition is cold boundary wall,the wall radition heat increases with increasing radiation absorption coefficient and decreases with increasing scattering albedo.(2)The radiation module is well coupled with the original flow module of GTEA.A detailed research for the closed square cavity containing an isotropic scattering medium involved coupled heat transfer between convection and radiation is performed based on the finite volume method.The effects of various influencing parameters such as,such as Planck number(0.0001?Pl?P10),attenuation coefficient(0.2??0?5),temperature rate(0.25???0.9),scattering albedo(0???1),the tilt angle(-60° ?? ?90°)and aspect ratio(1?AR?5)on the isotherm,flow lines,non-dimensional temperature,speed and Nusselt numbers are analyzed.(3)Calculate non-gray gas properties based on the combined wide and narrow band correlated k distribution model(CWNBCK).For radiation heat transfer of in-cylinder,the detailed spectral data is not necessary,the main concern in radiation heat transfer of the spectrum.According to the combined bands method of the literature,this paper will merged all narrow bands into two wide bands.The total absorb coefficient of the mixed gas of CO2 and H20 is calculated by using combined wide and narrow k distribution model.This method ensures the accuracy,saves CPU time and performs easily for the calculations gas radiation properties of in-cylinder.(4)The radiation heat transfer of particle droplets is taken into account.The original droplet evaporation module of GTEA ignores the influence of thermal radiation.In this paper,assume radiative energy could have effects on the droplet's surface with the similar mechanism to convection.The radiation heat transfer calculation program is completed based on simplified radiation heat absorption model developed by B.Abramzon and the best approximate expression for averaged absorption factor,which is brought forward by S.S.Sazhin and Dombrovsky.Single droplet case illustrate the effects of radiation heat transfer to the droplet diameter and temperature.When the temperature of gas is relatively low(673K),thermal radiation has a relatively small effect on the diameter and temperature of droplet.(5)Numerical simulation of radiation coupled with convection for two-phase gas stream flows in combustor has been achieved.With the use of GTEA's original modules for heat transfer,flow,spray and chemical reactions,as well as the newly added solution module in present work--calculation module for radiation equations,non-gray gas properties and heat transfer process of droplet radiation.The effect of droplets' radiation heat transfer and radiation of CO2 and H2O on the mean temperature and pressure and the instantaneous temperature of in-cylinder has been studied.The mean pressure of in-cylinder taking radiaiton heat transfer into account is more close to the experimental data.