【作者】 张宇；

【导师】 俞小莉； 刘震涛；

【作者基本信息】 浙江大学 ， 动力机械及工程， 2013， 博士

【摘要】 内燃机整机耦合仿真思想的提出至今已有20余年,近年来发展速度较快并逐渐成为指导内燃机设计的重要手段。尽管国内外众多学者应用该思想对多种机型进行了数值分析,然而至今还未能实现在统一的求解器中对流场、温度场和应力场等多物理场同时进行计算,仍然需要在不同的求解器中进行迭代。同时,内燃机功率密度的不断提高导致其热负荷水平的激增,为了有效控制高功率密度内燃机较高的热负荷对燃烧室组件可靠性的不利影响,同时优化整机性能,必须深入开展高功率密度条件下流动与传热的基础问题研究。本文以高功率密度内燃机高转速、高增压、高强度燃烧的特点为背景,建立了缸内工质循环的零维和多维数值模型,重点开展了缸内瞬时传热模型研究、高热流密度下燃烧室组件材料热物性的非线性效应研究,在此基础上建立了缸内燃气-燃烧室组件-冷却介质的共轭传热数值计算模型,较深入地研究了燃烧、冷却、材料、结构等因素对高功率密度柴油机燃烧室组件热状态的影响规律。主要研究内容及所得的重要结论包括：1、基于热力学、流体力学、传质传热学和化学反应动力学建立了缸内工质循环过程的数值计算模型,比较了零维模型和多维模型在计算结果上的差异,并分析了两种模型的优势和不足,为后续研究燃气侧边界条件的修正方法提供了理论依据。2、开展了缸内瞬态传热模型的研究。对比分析了零维模型中几种常用经验公式在不同机型上的适用性以及多维模型中壁面函数法在燃烧室组件温度场计算中的适用性,在此基础上提出了适用于高功率密度柴油机传热计算的新的经验公式以及分布函数,并用试验数据对其进行了验证。研究结果表明,随着热流密度的增加,利用传统经验公式进行燃烧室组件温度场计算时,仿真结果与试验数据的最大相对误差接近30%；修正后的经验公式及其分布函数在高功率密度柴油机稳态传热计算中获得了较好的应用,与试验测试值的偏差小于5%。3、收集和测试了燃烧室组件特殊材料的导热系数、比热容、热膨胀系数、密度等热物性随温度变化的特征数据,对比分析了高热流密度条件下平板模型的非线性传热本构方程的解析解与数值解的差异,掌握了不同热流密度传热条件下平板内部温度分布的变化规律,并通过感应加热平板试验验证了材料物性的非线性效应。随后对活塞等复杂结构的零件的导热过程分别开展了稳态和瞬态条件下的数值计算及试验研究。研究结果表明,当热流密度超过1500kW/m2时,常物性设置与变物性设置所得到的计算结果之间的最大相对误差超过10%；在大规模计算时,变物性设置所用的计算时间比常物性设置多出20%-30%；在高功率密度柴油机共轭传热计算中,活塞、缸盖、缸套等热负荷水平较高的零部件,其热物性需要设置为阶梯函数形式。4、建立了缸内气体-燃烧室组件-冷却介质的共轭传热数值计算模型。该模型将上述研究所获得的缸内瞬时传热模型、固体区域非线性导热模型结合在一起,获得了较高精度的数值解。同时在某试验机型上开展了整机热状态测量试验,测试了燃烧室组件的温度分布状态,验证了仿真计算的精度。研究结果表明,该模型能显著提升高功率密度柴油机燃烧室组件传热计算的精度,仿真计算结果与试验值之间的偏差小于5%,而传统模型的仿真计算结果与试验值之间的偏差接近30%。5、在仿真计算中,通过改变热侧和冷侧的边界条件,计算分析了燃烧和冷却因素对燃烧室组件热状态的影响；通过改变燃烧室组件结构和材料热物性,计算分析了结构、材料等因素对燃烧室热状态的影响。根据以上分析结果,梳理了燃烧、冷却、结构和材料各因素对燃烧室组件热状态的耦合影响规律。研究结果表明,在诸多因素中,冷却液流量对燃烧室组件热状态影响最为明显,冷却液流速的增高可有效改善受热表面的温度场分布;其次为水腔结构,在保证强度的前提下,应使水腔尽可能地接近受热表面。更多还原

【Abstract】 Multiphysics coupled methods for internal combustion engine simulation has been developed more than20years and become an important design means of combustion chamber components. Although this numerical analysis method had applied on various types of IC engines, multi-flied in IC engine such as velocity field, temperature field and stress field still failed to calculation in a single solver. At the same time, increasing engine power density causes proliferation of the heat transfer throughout the chamber surface, which has adverse impact on the thermal loading and reliability of the combustion chamber components. In order to effectively control the thermal loading and optimize the engine performance, the fundamental problems of heat and mass transfer must be depth studied under the conditions of High Power Density (referred to as HPD).Considering the characteristics of HPD engine, such as high speed, high supercharge pressure, high-intensity combustion, a conjugate formulation to predict spray combustion in cylinder, heat conduction in combustion chamber components, and convection in coolant was developed for multi-dimensional HPD engine simulation. The formulation was first calculated in CFD code and then validated against experimental result.The main contents in this thesis are listed below:1, Combining thermodynamics, fluid mechanics and chemical kinetics, zero-dimensional and multidimensional numerical model for engine operation simulation was established in chapter two. The advantages and disadvantages of the two models were analyzed exactly. The result in this chapter provided a theoretical basis for further study of in-cylinder heat transfer models.2, Compared the numerical results between semi-empirical formula and wall function approach, a new in-cylinder heat transfer model was developed for HPD engine simulation and then validated by experimental data.With the increase of heat flux, the relative error of using traditional semi-empirical formula to predict components temperature is up to30%. Results show that the new in-cylinder heat transfer model developed in this paper is more suitable for HPD engine simulation.3, Materials thermal properties under different temperature, including thermal conductivity, specific heat capacity, expansion coefficient, were exactly tested by special equipment. Based on this data, nonlinear heat conduction equations of combustion chamber components were solved by numerical and analytical method.Results show that the temperature calculated by assuming material thermal properties as constant is larger10%than that of setting the properties as a function of temperature. For complex geometry, the non-linear heat conduction equation costs20%to30%computer resources more than the linear equation. Considering both calculation accuracy and time, it is better to use non-linear formula in cylinder head, piston and liner, at the same time to use linear formula in the rest parts of HPD engine.4, a conjugate formulation to predict heat conduction in components solid domain and convection in fluid domain was established for HPD engine simulation. The formulation had integrated the new in-cylinder heat transfer model and the nonlinear conduction model. Finally, the numerical solution of the conjugate formulation was validated against the test data of the HPD engine under different operating conditions.Results show that the conjugate formulation significantly improves the solution accuracy. The relative error between calculation data and test data is less than5%.5, the analysis of the conjugate formulation under different boundary conditions had subsequently revealed the interaction among various factors of HPD engine, such as combustion and cooling conditions, material properties and components structures.Results show that the cooling conditions have the greatest impact on the heat transfer in HPD engine among the four factors. Increasing the coolant velocity can effectively reduce the temperature at components inner surfaces. Secondly, permitting the components structural strength, the smaller distance between the cooling jacket and heated surfaces has the better cooling effect.更多还原