Study On Effect Of Heat Transfer Time And Space Non-uniformity Of Combustion Chamber Components On Working Process In Internal Combustion Engine

Internal combustion engine design is including three parts,among them heat transfer process is of the most importance and has great influence on all kinds of engine performance, especially on in-cylinder working process.So in order to predict power,emission and in-cylinder process principle of internal combustion engine accurately,it is very important to study how heat transfer affects in cylinder working process.However,if the heat transfer process information of internal combustion engine needs to be known in detail,it is necessary to adapt coupled complete model simulation technology that working process,combustion chamber components,cooling system and lubrication system are coupled to one model in which muti-dimentional physical field simulation is done.Recently numerical simulation technology of internal combustion engine is getting more and more advanced that make it possible to finish such complicated simulation in this study.In this paper coupled complete model simulation technology is applied to actual heat transfer process simulation of internal combustion engine to realize the effect of heat transfer of combustion chamber components on in-cylinder working process,therefore,in return simulation technology of internal combustion engine is improved further.1.Under the thought of coupled complete model simulation,dynamic and static contact coupled heat transfer models between in-cylinder working process and combustion chamber components,between combustion chamber components and cooling system,among combustion chamber components were built to simulate coupled heat transfer among combustion chamber components in three dimensional steady and transient state.Results show that it is reliable and accurate to make such numerical simulation on heat conduction among combustion chamber components with the coupled components method and coupled fluid and solid technology.Steady coupled heat transfer simulation shows great temperature non-uniform distribution on the surface of all combustion chamber components,the greatest temperature difference on piston crown is 84℃;the greatest temperature difference inside cylinder liner along axial direction is 130℃,comparatively the temperature difference inside cylinder liner along circumferential direction is small;the non-uniform temperature distribution on cylinder head bottom is apparent,the greatest difference is 165.1℃;Transient coupled heat transfer simulation shows that for normal metal built diesel engine under stable working state surface temperature of combustion chamber components fluctuates with 20℃in amplitude and 2mm in depth.2.Quasi-dimensional mathematic model of working process on diesel engine was built and its accuracy was proved by performance tests.On this base the effect of heat transfer time non-uniformity of combustion chamber components on performance of diesel engine was studied.Results show the non-uniform temperature distribution on surface of combustion chamber components has little effect on power,economy and emission for normal metal built diesel,and has certain effect on heat transfer performance,however its amplitude is less than 1%.At the same time the effect of wall temperature variation amplitude on diesel engine performance was also studied.The results show when the temperature variation amplitude is less than 20℃there is little effect on engine performance which can even be ignored. However when the temperature variation amplitude is over 100℃,there is obvious effect on power,economy and emission of diesel engine,especially on emission performance,when the temperature amplitude varies 100℃,the NOx increases 14.9%,the soot increases 16.5%. Thus it can be seen that when the temperature variation of combustion chamber components surface in transient state and adiathermal situation is over 100℃the time non-uniformity of surface temperature distribution can not be ignored.3.Multi-dimensional transient numerical simulation model of in-cylinder working process including radiation heat transfer model was built.After comparing the simulation results of wall unit characteristic radial quantity from different wall models,convection heat transfer model and radiation heat transfer model(DTRM model),it is found that the compound wall function method which combines low Reynolds number model and standard wall function makes in-cylinder multi-dimensional numerical simulation more approximate to test results.The computation result of Han-Reitz model is more approximate to test results compared with standard wall heat transfer model.When in-cylinder radiation is simulated with DTRM method and boundary unit wall characteristic radial quantity is over 16 the computation results are hardly influenced by the characteristic radial quantity.Furthermore the effect of the combustion chamber surface radiance and spray advance angle on in-cylinder working process was analyzed using optimized multi-dimensional mathematic model,and the effect of different heat transfer models on the whole heat transfer loss was also studied. Results show in-cylinder emission formation is mainly influenced by combustion chamber surface radiance,the highest pressure and temperature in cylinder raises when spray advance angle increases,and therefore heat transfer inside cylinder wall increases,consequently,NO_x increases and Soot reduces.In different spray advance angle the predicted in-cylinder pressure curve can fit test curve well that proves the accuracy of the mathematic models involved in the multi-dimensional transient numerical simulation and the reliability of the application of whole model simulation.In addition the results show radiation heat transfer accounts for about 30%of the total heat transfer in diesel engine cylinder and heat transfer of piston accounts for 60%of the total heat loss.4.On the base of multi-dimensional transient numerical simulation of in-cylinder working process three dimensional coupled computation model which combines in-cylinder working process and combustion chamber components was built using partition solution method and boundary coupled method.So three dimensional complete model simulation by coupling in-cylinder working process and combustion chamber parts was realized and the effect of heat transfer space no-uniformity on in-cylinder heat transfer,flow,spray, combustion and emission is studied.Results show the effect of wall temperature space no-uniform distribution of combustion chamber components on heat transfer happens mainly at the end of compression stroke and expansion stroke.Therefore it can be concluded that wall temperature space no-uniform distribution of combustion chamber components would influence heat transfer during intake and exhaust stroke obviously.The wall temperature space no-uniform distribution of combustion chamber components is hardly related to in-cylinder gas flow,which is mainly dependent on the combustion chamber components structure,intake system structure,fuel spray nozzle structure,nozzle position and spray intensity.From the results of fuel atomization simulation it can be known the wall temperature space no-uniform distribution of combustion chamber components has certain influence on fuel atomization at the initial and middle stage of spray,mainly in the bottom space of combustion chamber and near cylinder wall.At the late stage of spray in-cylinder gas temperature is mainly dependent on fuel combustion,not on heat transfer of cylinder wall,so the wall temperature space no-uniform distribution of combustion chamber components has nearly no effect on spray.However at this time radiation heat transfer acts on spray remarkably that result in heat transfer increasing and spray getting worse.The heat transfer space no-uniformity of combustion chamber components has certain effect on CO₂ formation during spray and reduces gradually until late combustion stroke.For CO the situation is on the contrary.In addition radiation heat transfer influences the whole combustion process deeply. The heat transfer space non-uniformity of combustion chamber components directly influences the formation of NO_x and convection heat transfer space non-uniformity mainly influences the formation of NO_x near combustion chamber wall surface.The radiation heat transfer space non-uniformity mainly influences the formation of NO_x within combustion chamber space and not near the wall surface.The heat.transfer space non-uniformity of combustion chamber components has little effect on soot formation,far less than on NO_x.