REACTION MODELING OF AUTO-IGNITION AND EXHAUST EMISSION IN COMPRESSION-IGNITION COMBUSTION

针对柴油机压缩点火过程，建立了三种不同类型的反应模型，并结合尾气排放分析。第一个模型描述了燃料高温氧化生成CO和H_2的过程，采用一步全局Edelman机制，然后详细描述了CO和H_2的氧化动力学。除上述模型外，还考虑了快速NO和热NO的形成模型。这些反应被整合到随机模型中，该模型表达了不同温度和物质浓度的气体团在湍流混合中的随机碰撞。计算结果与柴油机尾气中NO浓度的实测结果比较吻合。第二种模型不仅表达了热释放过程，而且还表达了裂解过程，这是模拟烟灰形成的关键。该模型基于Rice-Herzfeld机理和C_2烃化学，由以下多步反应组成：c_mh_n *aC_2H_4+bC_4H_9: n-C_4H_9*C_2H_4+C_2H_5；通过与快速压缩机测得的点火延迟进行比较，得到了上述反应的速率常数。计算得到的CH_4、C_2H_4、C_2H_6和C_3H_6的分数与测量值吻合较好。第三个模型描述了分析预混合压缩-点火过程所需的低温氧化机理。在Keck模型的基础上，通过修改速率常数、活化能和终止反应机理来拟合已有的实验结果，建立了该模型。本研究建立的模型将为正在开发的一种潜在的未来内燃机提供一种更现实的模型，以结合高低温机制来研究预混合压燃发动机的自燃过程。

Three different types of reaction models have been developed for the compression-ignition process in Diesel engines to be coupled with exhaust emission analyzes.The first model is to describe the high temperature oxidation process from fuel to CO and H_2 with one-step global mechanism of Edelman followed by a detailed kinetics of the oxidation of CO and H_2. In addition to these models, a model for NO formation including prompt NO and thermal NO were taken into account. These reactions were integrated in the stochastic model which expressed the random collisions in turbulent mixing between gas blobs having different temperatures and species concentrations. The computed results compared well with measurements of NO concentration in Diesel exhaust.The second model expresses not only the heat release but also the cracking process which is essential to modeling the soot formation. The model consists of following multi-step global reactions based on the Rice-Herzfeld mechanism and the C_2 hydrocarbon chemistry.C_mH_n*aC_2H_4+bC_4H_9 : n-C_4H_9*C_2H_4+C_2H_5 ; i-C_4H_9*C_3H_6+CH_3The rate constant for the above global reaction was obtaned by comparing with the ignition delay measured in a rapid compression machine. The computed fractions of CH_4, C_2H_4, C_2H_6 and C_3H_6 showed good agreement with measurements.The third model describes the low temperature oxidation mechanism which is needed to analyze a premixed compression-ignition proces. Based on Keck's model, the model has been established by modifying rate constants, activation energies and the mechanism of the termination reaction to fit existing experimental results.The models developed in this study will lead to a more realistic model to combine the high and low temperature mechanisms for the auto-ignition process in the premixed compression-ignition engines being developed for one of the potential future internal combustion engines.