Large eddy simulation of spray and combustion characteristics with realistic chemistry and high-order numerical scheme under diesel engine-like conditions
Large eddy simulation of spray and combustion characteristics with realistic chemistry and high-order numerical scheme under diesel engine-like conditions
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DOI：
10.1016/j.enconman.2015.01.033
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发表时间：
2015-03
影响因子：
10.4
通讯作者：
Lei Zhou;K. Luo;Wenjin Qin;M. Jia;Shi-jin Shuai
中科院分区：
文献类型：
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作者：
Lei Zhou;K. Luo;Wenjin Qin;M. Jia;Shi-jin Shuai
湍流燃烧大涡模拟的准确性取决于合适的数值格式和化学机理。在原有的KIVA 3V程序中，采用准二阶迎风格式（QSOU）和部分施主单元差分格式（PDC）等有限差分格式，由于数值扩散大，在使用粗网格时不能取得很好的结果，甚至不能保证计算稳定性。本文将MUSCL（Monotone Upstream-centered Schemes for Conservation Laws）差分格式应用到KIVA 3V-LES程序中计算对流项。与此同时，Lu的正庚烷还原58种机制（Lu，2011）用于通过并行算法计算化学。最后，还采用了改进的喷雾喷射模型。通过这些改进，KIVA 3V-LES代码在本研究中被重命名为KIVALES-CP（化学与并行算法）。在定容容器内模拟了柴油机工况下的气液两相射流和燃烧过程。结果表明，使用MUSCL格式可以准确地捕捉喷雾形状和燃料蒸汽渗透，即使在一个粗糙的网格，与桑迪亚实验数据进行比较。对于具有非常不同的物理性质的三种单组分燃料，异辛烷（C8 H18）、正十二烷（C12 H26）和正十六烷（C16 H34），也获得了类似的良好结果。同时，在定容燃烧室中，当环境温度从850 K增加到1300 K，环境密度从14.8 kg/m3增加到30.0 kg/m3，氧浓度从10%增加到21%时，改进的方法能够准确预测着火延迟期和火焰升离长度。随着氧气浓度的增加，点火延迟时间和因此火焰LOL减小，因为火焰如预期地向上游移动。另一方面，降低环境温度从1000 K到900 K延迟自燃时间和移动燃烧位置下游下不同的氧气浓度。
The accuracy of large eddy simulation (LES) for turbulent combustion depends on suitably implemented numerical schemes and chemical mechanisms. In the original KIVA3V code, finite difference schemes such as QSOU (Quasi-second-order upwind) and PDC (Partial Donor Cell Differencing) cannot achieve good results or even computational stability when using coarse grids due to large numerical diffusion. In this paper, the MUSCL (Monotone Upstream-centered Schemes for Conservation Laws) differencing scheme is implemented into KIVA3V-LES code to calculate the convective term. In the meantime, Lu’s n-heptane reduced 58-species mechanisms (Lu, 2011) is used to calculate chemistry with a parallel algorithm. Finally, improved models for spray injection are also employed. With these improvements, the KIVA3V-LES code is renamed as KIVALES-CP (Chemistry with Parallel algorithm) in this study. The resulting code was used to study the gas–liquid two phase jet and combustion under various diesel engine-like conditions in a constant volume vessel. The results show that using the MUSCL scheme can accurately capture the spray shape and fuel vapor penetration using even a coarse grid, in comparison with the Sandia experimental data. Similarly good results are obtained for three single-component fuels, i-Octane (C8H18), n-Dodecanese (C12H26), and n-Hexadecane (C16H34) with very different physical properties. Meanwhile the improved methodology is able to accurately predict ignition delay and flame lift-off length (LOL) under different oxygen concentrations from 10% to 21% with ambient density increasing from 14.8 kg/m3to 30.0 kg/m3and ambient temperatures from 850 K to 1300 K in a constant volume combustion chamber. With increasing oxygen concentration, the ignition delay time and consequently the flame LOL decrease, as the flame moves upstream as expected. On the other hand, reduction in the ambient temperature from 1000 K to 900 K retards the auto-ignition time and moves the burning location downstream under different oxygen concentrations.