This article describes the application of a modified first-order conditional moment closure model used in conjunction with the trajectory-generated low-dimensional manifold method in large-eddy simulation of pilot ignited high-pressure direct injection natural gas combustion in a heavy-duty diesel engine. The article starts with a review of the intrinsic low-dimensional manifold method for reducing detailed chemistry and various formulations for the construction of such manifolds. It is followed by a brief review of the conditional moment closure method for modelling the interaction between turbulence and combustion chemistry. The high computational cost associated with the direct implementation of the basic conditional moment closure model was discussed. The article then describes the formulation of a modified approach to solve the conditional moment closure equation, whose reaction source terms for the conditional mass fractions for species were obtained by projecting the turbulent perturbation onto the reaction manifold. The main model assumptions were explained and the resulting limitations were discussed. A numerical experiment was conducted to examine the validity the model assumptions. The model was then implemented in a combustion computational fluid dynamics solver developed on an open-source computational fluid dynamics platform. Non-reactive jet simulations were first conducted and the results were compared to the experimental measurement from a high-pressure visualization chamber to verify that the jet penetration under engine relevant conditions was correctly predicted. The model was then used to simulate natural gas combustion in a heavy-duty diesel engine equipped with a high-pressure direct injection system. The simulation results were compared with the experimental measurement from a research engine to verify the accuracy of the model for both the combustion rate and engine-out emissions.

中文翻译：

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基于低维流形法的修正条件力矩闭合模型对重型卡车发动机直喷天然气燃烧的大涡模拟

本文描述了改进的一阶条件矩闭合模型与轨迹生成的低维流形方法在重型柴油机中引燃高压直喷天然气燃烧的大涡模拟中的应用。引擎。本文首先回顾了用于减少详细化学过程的固有低维流形方法和构建此类流形的各种公式。随后简要回顾了用于模拟湍流和燃烧化学之间相互作用的条件矩闭合方法。讨论了与直接实现基本条件矩闭合模型相关的高计算成本。然后，文章描述了求解条件矩闭合方程的修改方法的公式，该方程的条件质量分数的反应源项是通过将湍流扰动投影到反应歧管上来获得的。解释了主要模型假设并讨论了由此产生的局限性。进行了数值实验以检验模型假设的有效性。然后在开源计算流体动力学平台上开发的燃烧计算流体动力学求解器中实施该模型。首先进行非反应性射流模拟，并将结果与​​高压可视化室的实验测量结果进行比较，以验证正确预测了发动机相关条件下的射流穿透。该模型随后用于模拟配备高压直喷系统的重型柴油发动机中的天然气燃烧。将仿真结果与研究发动机的实验测量结果进行比较，以验证模型在燃烧率和发动机排放方面的准确性。