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本文介绍一种在用特征线法计算排气管内压力波时,模件式脉冲转换器(简称MPC)边界的计算模型。该模型考虑了排气支管内气体与管壁间的传热、摩擦,管段的变截面、弯曲、非圆截面等因素,同时将弯管损失系数折合成摩擦系数。变截面支管与总管连接处的边界按普通三分支边界处理,但根据MPC结构的特点,压力损失系数不再选用固定不变的常数,而是采用经过修正的稳流试验下得到的经验公式,在这些经验公式中,压力损失系数不仅与相连的各管段间的流速比有关,同时还和支管与总管间的夹角,各管段间的截面比等因素有关。这样处理不仅计算简单,而且能较好地反映排气管内的压力波动情况。此计算模型的合理性和可靠性已被在6135ZD柴油机上获得的试验结果所证实。
This paper introduces a calculation model of the modular pulse converter (MPC) boundary when using the characteristic line method to calculate the pressure wave in the exhaust pipe. The model takes into account the heat transfer between the gas and the wall of the exhaust manifold, friction, the variable section of the pipe section, bending, non-circular cross section and other factors, while the elbow loss coefficient equivalent to the friction coefficient. However, according to the characteristics of MPC structure, the pressure loss coefficient is no longer selected constant, but the empirical formula obtained by the modified steady flow test, In these empirical formulas, the pressure loss coefficient is not only related to the flow rate ratio between the connected pipe sections, but also relates to the angle between the branch pipe and the main pipe and the section ratio between the pipe sections. This treatment is not only simple calculation, but also to better reflect the exhaust pipe pressure fluctuations. The rationality and reliability of this computational model have been demonstrated by the experimental results obtained on a 6135ZD diesel engine.