【作者】 吕继组；

【导师】 白敏丽；

【作者基本信息】 大连理工大学 ， 工程热物理， 2009， 博士

【摘要】 作为内燃机设计三大组成部分之一的传热过程对内燃机的各种性能都有着至关重要的影响,特别是对工作过程的影响更为突出。因此,研究内燃机传热对工作过程的影响,对准确预测内燃机动力性、排放和缸内过程等都有十分重要的作用。另外,鉴于内燃机数值模拟技术的不断成熟,为了利用数值模拟方法对内燃机传热进行详细预测,需要采用耦合全仿真模拟技术,即将内燃机工作过程、燃烧室部件、冷却系统、润滑系统等耦合起来作为一个整体,进行多维多物理场的模拟计算。本文正是致力于将内燃机全仿真模拟方法应用于实际内燃机传热模拟计算中,进一步推动内燃机模拟仿真技术的发展。通过模拟计算考察燃烧室部件传热对工作过程的影响。1.利用耦合全仿真模拟思想,建立了缸内工作过程与燃烧室部件、燃烧室部件与冷却系统以及燃烧室部件之间动接触和静接触的耦合传热模型,从而实现燃烧室部件耦合传热的三维稳态和瞬态数值模拟计算,结果表明采用部件耦合法和流固耦合技术对燃烧室固体部件的导热问题进行模拟计算是准确可靠的;稳态耦合传热模拟计算结果显示所有燃烧室部件表面温度分布都呈现极大的空间非均匀性,活塞顶面最大温差为84℃;气缸套在缸内空间范围内壁面沿轴向最大温度差为130℃,周向温度的分布相对来说较为均匀,温差较小,气缸盖火力面范围内温度分布的空间非均匀性最为明显,最大温差为165.1℃;瞬态耦合传热模拟计算结果显示常规金属柴油机在稳定工作状态下,燃烧室部件表面温度随时间的波动幅度小于20℃,深度小于2mm。2.对柴油机工作过程建立准维数学模型,并利用性能试验验证了整体模型的准确性,且在此基础上考察燃烧室部件传热时间非均匀性对柴油机性能的影响。结果表明燃烧室部件传热时间非均匀性对常规金属柴油机的动力性、经济性和排放的影响十分微小,对传热性能有一定影响,但幅度也小于1%。同时模拟壁面温度变化对柴油机性能的影响,结果显示当温度变化＜20℃时,其变化对发动机性能的影响十分微小,可以忽略不计;但温度变化超过100℃以后,其变化对柴油机传热、动力性、经济性和排放的影响显著加剧,特别是对排放的影响,温度变化100℃时,NO_x的生成相差14.9%,碳烟的生成相差16.5%。由此可见,对绝热发动机燃烧室部件壁面循环瞬态温度波动超过100℃时,壁面温度分布的时间非均匀性不能忽略。3.建立缸内工作过程的多维瞬态数值模拟计算模型,特别是辐射换热模型。通过对比不同壁面流动模型、壁面对流换热模型和辐射换热的模拟计算结果发现,壁面流动模型中复合壁函数法由于是低雷诺数模型和标准壁函数相结合的方法,使缸内多维模拟计算结果更接近于试验值;Han-Reitz模型和标准壁面传热模型比较,其计算结果更接近于试验值:使用DTRM方法对缸内辐射进行计算时,边界单元体壁面特征射线假定数目超过16以后,边界单元体壁面特征射线数量的变化对模拟计算影响极小,可以忽略;燃烧室部件壁面辐射率的变化主要影响壁面辐射热流密度和排放物的生成;辐射换热占柴油机缸内总传热量的30%左右,而活塞传热量占整体热损失的60%左右。进一步利用已经建立的多维数学模型,探讨喷雾提前角对缸内工作过程和传热的影响并进行校验。结果发现不同喷雾提前角状态下缸内压力的预测曲线与试验曲线吻合较好,进一步说明整个缸内工作过程的多维瞬态数值模拟中各种数学模型的准确性和整体模拟计算的真实性;喷雾提前角的加大会造成缸内最高压力、最高温度的提高,进而使缸内壁面换热量增加,从而影响到缸内的燃烧和排放,使NO_x的生成量增加,Soot的生成量降低。4.在缸内工作过程多维瞬态数值模拟计算校验基础上,利用分区求解、边界耦合法建立了缸内工作过程与燃烧室部件的三维耦合计算模型,从而实现了缸内工作过程与燃烧室部件的耦合三维全仿真模拟计算,以此考察燃烧室部件传热空间非均匀性对缸内传热、流动、喷雾、燃烧和排放的影响,结果表明燃烧室部件壁面温度的空间非均匀分布对传热的影响主要是在压缩过程和膨胀过程后期,由此可推断在进气过程和排气过程中燃烧室部件表面温度分布的非均匀性对传热会有较为明显的影响;燃烧室部件壁面温度的空间非均匀分布对缸内气体流动几乎没有任何影响,缸内流动主要取决于燃烧室部件结构、进气系统部件结构以及喷油嘴结构、喷孔位置和喷射强度等;燃油的雾化效果的计算结果发现,喷雾初期和中期燃烧室部件壁面温度的空间非均匀分布对燃油的雾化有一定影响,主要影响燃烧室底部空间和壁面附近区域,在喷雾后期,此时缸内气体温度主要取决于燃油的燃烧,壁面换热的影响本身就极小,因此壁面温度分布的空间非均匀性对雾化的影响也极小,但辐射传热对燃油雾化效果会产生显著影响,换热量的增加使整体雾化效果下降;喷雾过程燃烧室部件传热空间非均匀性对燃烧产物CO₂的生成会产生一定影响,而燃烧过程后期这种影响逐渐减弱,其对中间产物CO的生成的影响则相反,另外,辐射换热对整个燃烧过程起到至关重要的决定性作用;燃烧室部件传热空间非均匀性影响最明显的是NO_x的生成,对流换热的空间非均匀性主要影响燃烧室壁面附件区域内NO_x的生成,辐射换热的空间非均匀性主要影响整个燃烧室空间内部NO_x的生成,在燃烧室部件壁面附件区域内的影响较小;燃烧室部件传热空间非均匀性对碳烟生成的影响要远远小于对NO_x生成的影响。更多还原

【Abstract】 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.更多还原