This study proposed a hybrid model consisting of a characteristic time combustion (CTC) model and a closed reactor model for the combustion modelling with detailed chemistry in RCCI engines. In the light of the basic idea of the CTC model of achieving chemical equilibrium in high temperature, this hybrid model uses the CTC model to solve the species conversion and heat release in the diffusion flame. Except for the diffusion flame, the auto-ignition in RCCI combustion is computed by a closed reactor model with the CHEMKIN library by assuming that the computational cells are closed reactors. The border of the transition between the CTC model and closed reactor model is determined by two criteria, a critical temperature and a critical Damköhler number. On the formulation of this hybrid model, emphasis is placed on coupling detailed chemistry into this hybrid model. A CEQ solver for species equilibrium calculations at certain temperature, pressure was embedded with CTC for detailed chemistry calculation. Then this combustion model was integrated with the CFD framework KIVA4 and the chemical library CHEMKIN-II and validated in a RCCI engine. The predicted in-cylinder pressure and heat release rate (HRR) show a good consistency with the data from the experiment and better accuracy than that computed from the sole closed reactor model. More importantly, it is observed that this model could save computational time compared with closed reactor model due to less stiff ordinary differential equations (ODEs) computation. A sensitivity analysis of the critical temperature and critical Damköhler number was conducted to demonstrate the effect of these two parameters in the current model.

这项研究提出了一个混合模型，该模型由特征时间燃烧（CTC）模型和密闭反应堆模型组成，用于RCCI发动机的详细化学燃烧模型。根据CTC模型在高温下达到化学平衡的基本思想，该混合模型使用CTC模型来解决扩散火焰中的物质转化和热量释放。除扩散火焰外，RCCI燃烧中的自燃是通过带有CHEMKIN库的密闭反应堆模型通过假定计算单元为密闭反应堆来计算的。CTC模型和密闭反应堆模型之间的过渡边界由两个标准（临界温度和临界Damköhler数）确定。根据这个混合模型的公式，重点是将详细的化学反应耦合到该混合模型中。将CEQ求解器用于在特定温度和压力下进行物种平衡计算，并将其嵌入CTC中以进行详细的化学计算。然后将此燃烧模型与CFD框架KIVA4和化学库CHEMKIN-II集成在一起，并在RCCI发动机中进行了验证。预测的缸内压力和放热率（HRR）与实验数据显示出良好的一致性，并且比单独的密闭反应器模型计算出的精度更高。更重要的是，由于闭式常微分方程（ODE）的计算量较小，因此与封闭反应堆模型相比，该模型可以节省计算时间。