某发动机紧耦合式排气歧管热结构分析

发布时间：2018-05-06 02:22

本文选题：紧耦合式排气歧管 + 流固耦合　；参考：《重庆理工大学》2016年硕士论文

【摘要】：近年来发展起来的紧耦合式排气歧管能够很好的解决汽车冷启动阶段污染物排放的问题,这是因为三元催化器与排气歧管组合成一体,在冷启动阶段,催化剂能很快达到起燃催化温度,大大减少了污染物的排放量。作为新发展起来的一种排气歧管形式,目前学者们对紧耦合式排气歧管热结构性能的分析还比较少,又因为其结构形式、使用材料不同于传统的排气歧管,其长期承受高温和常温之间循环的温度作用,又受到来自周围部件传递来的振动激励作用,工作环境非常恶劣,所以有必要对其热结构性能进行分析研究。基于以上背景,本文对某企业新开发设计的一款紧耦合式排气歧管进行了热结构性能分析研究,主要目的是考察其是否满足使用要求。本文运用计算机数值模拟的方法,对该紧耦合式排气歧管从温度场、结构模态、热应力及低周热疲劳寿命等几个方面进行了热结构性能的计算分析。主要工作内容如下:(1)依据企业提供的发动机及排气系统设计参数,运用GT-power软件建立了带有排气系统的发动机一维仿真模型,并基于发动机的外特性实验数据验证了模型的合理性,最后得出了下一步计算分析所需的边界条件。(2)运用流体仿真软件STAR-CCM+与固体仿真软件ABAQUS联合仿真分析了流固耦合换热问题,依据HB5217-1982《金属低周热疲劳试验方法》,对该排气歧管进行非稳态流固耦合换热分析,通过计算得出了流体域外壁面的温度场和对流换热系数场,同时也得出了固体域的温度场。(3)基于上一步得到的固体域温度场,计算并分析了该排气歧管的热模态参数,并对其模态固有频率做了评价。计算了不同温度载荷下的结构约束热模态,总结出了温度载荷对结构模态的影响规律。(4)在周期循环温度载荷作用下,对该排气歧管结构的热变形、热应力、等效塑性应变进行了仿真分析,依据Manson-Coffin公式估算出了该排气歧管的低周热疲劳寿命。在以上分析结果的基础上,对该排气歧管进行了改进。分析结果表明:温度的升高对结构模态的固有频率有降低的效应,并且模态阶次越高降低的幅度越大,此排气歧管不会出现共振现象。四个支管汇合处的温度比较高,并且此区域的温度梯度大,产生的热应力超过了材料屈服强度,计算出了低周热疲劳寿命,表明该排气歧管可以满足使用要求,改进后的热结构性能有所提高。
[Abstract]:In recent years, the tightly coupled exhaust manifold developed in recent years can solve the problem of pollutant emission in the cold start stage of automobile. This is because the ternary catalytic converter and the exhaust manifold are combined together in the cold start stage. The catalyst can quickly reach the ignition catalytic temperature, greatly reducing the emission of pollutants. As a newly developed exhaust manifold form, there are few analyses on the thermal structure performance of the tightly coupled exhaust manifold, and because of its structure, the material used is different from the traditional exhaust manifold. It has been subjected to the effect of cycling temperature between high temperature and normal temperature for a long time, and it is also subjected to vibration excitation from the surrounding parts. The working environment is very bad, so it is necessary to analyze and study its thermal structure performance. Based on the above background, the thermal structure performance of a tightly coupled exhaust manifold developed by an enterprise is studied in this paper, the main purpose of which is to find out whether it meets the requirements of application. In this paper, the thermal structure properties of the tightly coupled exhaust manifold are calculated and analyzed in terms of temperature field, structural mode, thermal stress and low cycle thermal fatigue life by means of computer numerical simulation. The main work is as follows: (1) according to the design parameters of engine and exhaust system provided by the enterprise, the one-dimensional simulation model of engine with exhaust system is established by using GT-power software. The rationality of the model is verified based on the experimental data of the engine's external characteristics. Finally, the boundary conditions required for further calculation and analysis are obtained. The fluid-solid coupling heat transfer problem is analyzed by using the fluid simulation software STAR-CCM and the solid simulation software ABAQUS. According to HB5217-1982, metal low cycle thermal fatigue test method, the unsteady fluid-solid coupling heat transfer analysis of the exhaust manifold is carried out. The temperature field and convection heat transfer coefficient field of the outside wall of the fluid are calculated. At the same time, the temperature field of the solid region is obtained. (3) based on the temperature field obtained from the previous step, the thermal modal parameters of the exhaust manifold are calculated and analyzed, and the natural frequencies of the exhaust manifold are evaluated. The structure constrained thermal modes under different temperature loads are calculated, and the influence of temperature load on the structural modes is summarized. The thermal deformation and thermal stress of the exhaust manifold structure under the cyclic temperature load are summarized. The equivalent plastic strain is simulated and the low cycle thermal fatigue life of the exhaust manifold is estimated by Manson-Coffin formula. Based on the above analysis results, the exhaust manifold is improved. The results show that the increase of temperature has a decreasing effect on the natural frequency of the structure mode, and the higher the modal order is, the larger the amplitude is, and the resonance will not occur in the exhaust manifold. The temperature at the confluence of the four branch tubes is relatively high, and the temperature gradient in this area is large, which results in thermal stress exceeding the yield strength of the material. The low cycle thermal fatigue life is calculated, which indicates that the exhaust manifold can meet the requirements of application. The performance of the improved thermal structure has been improved.
【学位授予单位】：重庆理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U464.134.4

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