CFD modelling of cyclohexane auto-ignition in an RCM
CFD modelling of cyclohexane auto-ignition in an RCM
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DOI：
10.1016/j.fuel.2011.12.059
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发表时间：
2012-06
期刊：
影响因子：
7.4
通讯作者：
J. Griffiths;R. Piazzesi;E. Sazhina;S. Sazhin;P. Glaude;M. Heikal
中科院分区：
文献类型：
--
作者：
J. Griffiths;R. Piazzesi;E. Sazhina;S. Sazhin;P. Glaude;M. Heikal
基于综合动力学机理，对快速压缩机中环己烷自燃的动力学模型进行了研究，包括499种物质和2323个反应，然后减少到56种物质涉及196个反应和50种物质涉及143个反应。目的是探索简化动力学模型的优点，这些模型可以合并到计算流体动力学代码中，以对发动机中的燃料性能进行数值研究，特别是均质充气压缩点火（HCCI）或受控自动点火（CAI）。使用假设绝热反应的 SPRINT 零维代码，对空气中环己烷的化学计量混合物（包括 C6H12+9O2+33.86N2）进行点火延迟计算，初始压力为 0.48bar，在压缩气体温度范围 650–925K 下产生 7.2–9.7bar 的压缩气体压力。在整个压缩气体温度范围内，每个方案的预测延迟之间存在合理的一致性。预测了烷烃燃料的共同特征，即在中间范围内依赖于负温度的点火延迟。然而，与实验测量的一致性，特别是在负温度相关区域，并不十分令人满意。最初通过使用 SPRINT 的简单测试解决了导致差异的非绝热反应问题。然后，由 50 个物种组成的简化机制已被实施到多维 CFD 代码 FLUENT 中，这是该代码中可以合并的最大物种数。在封闭、恒体积绝热条件下，FLUENT 的预测与 SPRINT 的预测非常一致。当假设壁面非绝热时，FLUENT 计算显示温度梯度如何演变，从而导致反应发展速率的空间差异。特别地，在对应于点火延迟的负温度依赖性区域的压缩气体温度下，反应能够在边界层区域中更快速地发展，因此导致总体点火延迟相对于绝热条件下预测的减少。在这些情况下，点火本身是在边界层中引发的。
The kinetic modelling of cyclohexane auto-ignition in a rapid compression machine is addressed, based on the comprehensive kinetic mechanism, comprising 499 species and 2323 reactions, then reduced to 56 species involved in 196 reactions and 50 species involved in 143 reactions. The purpose is to explore the merits of reduced kinetic models that can be incorporated into Computational Fluid Dynamic codes for the numerical investigation of the performance of fuels in engines, with specific reference to Homogeneous Charge Compression Ignition (HCCI) or Controlled Auto-Ignition (CAI). Calculations of ignition delay, using the SPRINT zero-dimensional code assuming adiabatic reaction, have been performed for the stoichiometric mixture of cyclohexane in air, comprising C6H12+9O2+33.86N2, at an initial pressure of 0.48bar, yielding compressed gas pressures of 7.2–9.7bar over the compressed gas temperature range 650–925K. There is reasonable agreement between the predicted delays of each scheme over the whole range of compressed gas temperatures. The common feature for alkane fuels, of negative temperature dependent ignition delays in an intermediate range, is predicted. However, the agreement with experimental measurements, especially in the negative temperature dependent region, is not very satisfactory. Non-adiabatic reaction as a cause of the discrepancy is addressed, initially via simple tests using SPRINT. The reduced mechanism comprising 50 species has then been implemented into the multidimensional CFD code FLUENT, which is the maximum number of species that can be incorporated in this code. The predictions of FLUENT are in excellent agreement with those from SPRINT under closed, constant volume adiabatic conditions. When non-adiabaticity at the wall is assumed, the FLUENT calculations show how temperature gradients evolve, leading to spatial differences in the rates of development of reaction. In particular, reaction is able to evolve more rapidly in the boundary layer region at compressed gas temperatures that correspond to the region of negative temperature dependence of ignition delay, so causing a reduction in the overall ignition delay relative to that predicted under adiabatic conditions. Ignition itself is initiated in the boundary layer under these circumstances.