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PDF-based simulations of in-cylinder combustion in a compression-ignition engine

机译:压缩点火发动机中基于PDF的缸内燃烧模拟

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A transported probability density function (PDF) model is used to simulate the in-cylinder combustion processes in a compression-ignition heavy-duty engine. Heavy-duty vehicles are substantial users of petroleum-based fuels and significant contributors to greenhouse-gas emissions. For these reasons, it is essential to improve the efficiency and reduce the emissions in compression-ignition engines. Several advanced combustion strategies have been explored recently with the goal of decreasing the fuel consumption in compression-ignition engines for heavy-duty vehicles. These strategies include higher pressures, lower temperatures, varying degrees of fuel/air premixing and/or multiple fuels. Therefore, the combustion model should be able to deal with mixed-mode turbulent combustion under widely varying thermochemical conditions and should also be able to accommodate the use of multiple fuels and arbitrary numbers of liquid fuel injection events per engine cycle. The transported PDF model has the distinct advantage of handling all these conditions in a direct manner with minimal approximations. In this paper, recent results from in-cylinder combustion simulations using the transported PDF model for several operating conditions for a heavy-duty engine are presented. The computed pressure traces agree reasonably well with experimental data and respond correctly to variations in engine operating conditions. More importantly, significant differences are found between the results obtained using the transported PDF model that explicitly accounts for the turbulence/chemistry interactions (TCI) and those obtained using a model that do not account for TCI. Marked differences are observed in the computed flame structure and the global quantities between the two models. These differences indicate the extent to which unresolved turbulent fluctuations in composition and temperature influence the mean chemical reaction rates in a compression-ignition heavy-duty engine.
机译:传输的概率密度函数(PDF)模型用于模拟压缩点火重型发动机中的缸内燃烧过程。重型车辆是石油基燃料的大量用户和温室气体排放的重要贡献者。由于这些原因,必须提高效率并减少压缩点火发动机的排放。最近已经探讨了几种先进的燃烧策略,其目的是降低重型车辆压缩点火发动机的燃料消耗。这些策略包括较高的压力,较低的温度,不同程度的燃料/空气预混合和/或多个燃料。因此,燃烧模型应该能够在广泛改变的热化学条件下处理混合模式湍流燃烧,并且还应能够适应每个发动机循环的多个燃料和任意数量的液体燃料喷射事件。传输的PDF模型具有以最小近似的直接方式处理所有这些条件的明显优点。在本文中,介绍了使用输送的PDF模型的汽缸燃烧模拟的最近结果,用于几种用于重型发动机的若干操作条件。计算的压力迹线与实验数据相当良好地同意,并正确地响应发动机操作条件的变化。更重要的是,在使用传输的PDF模型获得的结果之间发现了显着估计湍流/化学相互作用(TCI)的结果,并且使用不考虑TCI的模型获得的结果。在计算的火焰结构中观察到显着的差异以及两种模型之间的全局量。这些差异表明了组合物和温度中未解决的湍流波动的程度影响压缩点火重型发动机中的平均化学反应速率。

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