OPOC发动机活塞热负荷研究

发布时间：2018-05-09 20:39

本文选题：活塞热负荷 + 内冷油腔　；参考：《山东大学》2015年硕士论文

【摘要】：目前发动机正朝着高功率密度、高可靠性、低油耗以及低排放的方向发展,导致发动机热负荷大幅度提高。而活塞作为发动机的关键零部件之一,其可靠性会直接影响发动机的整体性能,并且活塞的工作环境异常恶劣,在工作过程中活塞顶面始终受到高温燃气的周期性作用,所以活塞顶部往往承受很高的热负荷。为了保证活塞能够安全可靠的工作,必须对活塞进行有效的冷却,而活塞喷油强制振荡冷却是目前应用最广泛的冷却方式,对活塞内冷油腔中冷却机油的流动与传热特性研究不仅能够为内冷油腔的优化设计提供依据,而且可以为活塞的热负荷计算提供相对精确的传热边界条件。本文以带有内冷油腔的某水平双对置发动机活塞为研究对象,采用CFD数值模拟的方法对活塞内冷油腔中冷却机油的流动与传热特性进行了分析,并通过试验与数值模拟相结合的方法对不同转速工况下活塞的温度场进行了研究,具体内容包括：(1)选用VOF两相流模型与动网格技术并利用CFD软件对内冷油腔中冷却机油的流动传热特性进行研究,模拟分析了发动机在某一特定工况下油腔壁面的瞬态机油分布情况、瞬态换热系数分布情况,油腔不同壁面位置(上表面、中间内侧面、中间外侧面、下表面)处的换热系数、整个油腔的壁面换热系数以及机油填充率随曲轴转角的瞬态变化趋势,最后研究了壁面平均换热系数在油腔圆周方向上的变化趋势以及发动机转速的改变对冷却机油瞬态传热特性所产生的影响。(2)采用存储式活塞测温系统在整机试验台架上对活塞顶部五个关键位置处的温度值进行了测量,得到了测温点处的温度随不同发动机工况变化的动态响应曲线和各测点在稳态工况运行时的温度值,为研究活塞热负荷以及更为精确地修正温度场计算模型提供了依据。(3)采用GT-POWER软件对发动机整机热力循环过程进行模拟,得到了各工况下活塞顶面瞬时换热系数和瞬时温度,然后结合经验公式确定活塞顶面的稳态传热边界条件；同时,根据内冷油腔中冷却机油的CFD模拟计算和经验公式确定活塞内冷油腔和其余部位的传热边界条件；最后利用ABAQUS有限元计算软件对各工况下的温度场进行计算,并将各测点处的计算结果同试验值进行对比,发现最大误差为8.0%,说明计算结果较为合理。(4)针对活塞在高转速工况运行时活塞顶部温度偏高这一问题,研究了不同发动机转速与机油喷射压力工况下内冷油腔中冷却机油的传热特性以及冷却机油喷射压力的改变对活塞温度场的影响,发现通过提高喷油压力能够明显降低活塞顶部和环槽处的温度值,可以作为高功率密度发动机加强活塞冷却的改进方案。
[Abstract]:At present, the engine is developing towards the direction of high power density, high reliability, low fuel consumption and low emission. As one of the key parts of the engine, the reliability of the piston will directly affect the overall performance of the engine, and the working environment of the piston is abnormally bad, the top surface of the piston is always subjected to the periodic action of high temperature gas during the working process. So the top of the piston tends to bear a high thermal load. In order to ensure that the piston can work safely and reliably, it is necessary to cool the piston effectively, and the forced oscillation cooling of piston injection is the most widely used cooling method at present. The study on the flow and heat transfer characteristics of cooling oil in the piston inner cooling oil chamber can not only provide the basis for the optimization design of the inner cooling oil chamber, but also provide a relatively accurate heat transfer boundary condition for the calculation of the thermal load of the piston. In this paper, the flow and heat transfer characteristics of the cooling engine oil in the inner cooling oil chamber of the piston are analyzed by using CFD numerical simulation method, taking the piston of a horizontal double-contrast engine with an internal cooling oil chamber as the research object. The temperature field of the piston under different rotational speed conditions is studied by the combination of experiment and numerical simulation. The specific contents include: 1) selecting VOF two-phase flow model and dynamic grid technology and using CFD software to study the flow and heat transfer characteristics of cooling oil in the inner cooling oil chamber. The transient oil distribution, transient heat transfer coefficient and heat transfer coefficient at different wall positions (upper surface, middle inner side, middle outer side, lower surface) of the engine under a certain working condition are simulated and analyzed. The transient variation trend of wall heat transfer coefficient and oil filling rate with crankshaft angle of the whole oil chamber, Finally, the variation trend of wall average heat transfer coefficient in the circumferential direction of the oil chamber and the influence of the engine speed on the transient heat transfer characteristics of the cooling engine oil are studied. The temperature values at five key positions at the top of the piston were measured on the bench. The dynamic response curves of the temperature at the measuring points with different engine working conditions and the temperature values of the measured points in the steady state are obtained. In order to study the thermal load of piston and modify the model of temperature field more accurately, the thermal cycle process of engine is simulated by GT-POWER software, and the instantaneous heat transfer coefficient and instantaneous temperature of piston top surface are obtained under various working conditions. At the same time, according to the CFD simulation calculation and empirical formula, the heat transfer boundary conditions of the inner cooling oil chamber and other parts of the piston are determined. Finally, the temperature field under various working conditions is calculated by using ABAQUS finite element calculation software, and the calculated results at each measuring point are compared with the experimental values. It is found that the maximum error is 8.0, which shows that the calculation result is reasonable. (4) aiming at the problem that the top temperature of piston is on the high side when the piston is running at high rotational speed, The heat transfer characteristics of cooling engine oil in the cooling oil chamber under different engine speed and engine oil injection pressure and the influence of the cooling oil injection pressure on the piston temperature field are studied. It is found that by increasing the injection pressure, the temperature at the top of the piston and at the ring groove can be significantly reduced, which can be used as an improved scheme for enhancing the piston cooling of the high power density engine.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK403

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