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首页> 外文期刊>Combustion and Flame >Direct numerical simulations of ignition of a lean n-heptane/air mixture with temperature inhomogeneities at constant volume: Parametric study
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Direct numerical simulations of ignition of a lean n-heptane/air mixture with temperature inhomogeneities at constant volume: Parametric study

机译：恒定体积下温度不均匀的稀正庚烷/空气混合物着火的直接数值模拟：参数研究

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摘要

The effect of thermal stratification on the ignition of a lean homogeneous n-heptane/air mixture at con stant volume and high pressure is investigated by direct numerical simulations (DNS) with a new 58 species reduced kinetic mechanism developed for very lean mixtures from the detailed LLNL mechanism (HJ. Curran et al.. Combust. Flame 129 (2002) 253-280). Two-dimensional DNS are performed in a fixed volume with a two-dimensional isotropic velocity spectrum and temperature fluctuations superimposed on the initial scalar fields. The influence of variations in the initial temperature field, imposed by chang ing the mean and variance of temperature, and the ratio of turbulence to ignition delay timescale on multi-stage ignition of a lean n-heptane/air mixture is studied. In general, the mean heat release rate increases more slowly with increasing thermal stratification regardless of the mean initial temperature. Ignition delay decreases with increasing thermal stratification for high mean initial temperature relative to the negative temperature coefficient (NTC) regime. It is, however, increased with increasing thermal fluctuations for relatively low mean initial temperature resulting from a longer overall ignition delay of the mixture. Displacement speed and Damkohler number analyses reveal that the high degree of ther mal stratification induces deflagration rather than spontaneous ignition at the reaction fronts, and hence, the mean heat release rate is smoother subsequent to thermal runaway occurring at the highest temper ature regions in the domain. Chemical explosive mode analysis (CEMA) also verifies that mixing counter balances chemical explosion at the reaction fronts for cases with large temperature fluctuation. It is also found that if the ratio of turbulence to ignition delay timescale is short, resultant diminished scalar fluc tuations cause the overall ignition to occur by spontaneous ignition. However, the overall effect of turbu lence is small compared to the effect of thermal stratification. These results suggest that the critical degree of thermal stratification for smooth operation of homogeneous charge compression-ignition (HCCI) engines depends on both the mean and fluctuations in initial temperature which should be con sidered in controlling ignition timing and preventing an overly rapid increase in pressure in HCCI combustion.
机译：通过直接数值模拟（DNS），研究了热分层对恒定体积和高压下稀薄均相正庚烷/空气混合物着火的影响，其中采用了新的58种降低极稀薄混合物的动力学机理。 LLNL机制（HJ.Curran等人，Combust.Flame 129（2002）253-280）。在固定体积中执行二维DNS，并具有二维各向同性的速度谱和叠加在初始标量场上的温度波动。研究了改变温度的均值和方差以及湍流与点火延迟时间比例之比对初始温度场变化的影响对稀正庚烷/空气混合物的多级点火的影响。通常，不管平均初始温度如何，随着热量分层的增加，平均放热速率的增加会更缓慢。相对于负温度系数（NTC）方案，高平均初始温度下点火延迟随着热分层的增加而降低。但是，由于相对较长的混合物总着火延迟，相对较低的平均初始温度，其随着热波动的增加而增加。位移速度和Damkohler数分析表明，高度的热分层会引起爆燃，而不是在反应前沿自燃，因此，在该区域的最高温度区域发生热失控后，平均放热率更加平滑。化学爆炸模式分析（CEMA）还可以验证，对于温度波动较大的情况，混合计数器可以平衡反应前沿的化学爆炸。还发现，如果湍流与点火延迟时间标度之比较短，则标量波动减小会导致整体点火通过自燃发生。但是，与热分层效应相比，湍流的总体效应很小。这些结果表明，均匀充气压燃式（HCCI）发动机平稳运行的热分层临界程度取决于初始温度的平均值和波动，这在控制点火正时和防止压力过快升高时应予以考虑。在HCCI燃烧中。

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  • 来源
    《Combustion and Flame》 |2011年第9期|p.1727-1741|共15页
  • 作者

    Chun Sang Yoo; Tianfeng Lu; Jacqueline H. Chen; Chung K. Law;

  • 作者单位

    School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798. Republic of Korea;

    Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269, USA;

    Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551-0969, USA;

    Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, Nf 08544, USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    hcci; dns; n-heptane reduced mechanism; thermal stratification; auto-ignition; chemical explosive mode analysis;

    机译：hcci;dns;正庚烷还原机理;热分层自燃化学爆炸模式分析;

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