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A Numerical Investigation of Flame Lift-Off in Diesel Jets

机译：柴油机火焰升空的数值研究

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Flame lift-off heights are modeled in diesel jets by using diffusion fla-melet extinction as a criterion for identifying the lift-off. It is shown that the axial distance in the jet where the stoichiometric scalar dissipation rate matches computed extinction scalar dissipation rate correlates with the lift-off height. The influence of injection pressures (40-138 MPa), chamber densities (14.8-58.5 kg/m~3), chamber temperatures (1000-1300 K) and O_2 molar concentrations (10-21%) are studied. N-heptane is chosen as a surrogate for diesel fuel. Two chemical kinetic mechanisms, a 37-species, 56-step mechanism and a 159-species, 1540-step mechanism, are employed. Consistent with experimental findings, the computed results indicate that the flame lift-off height decreases with increase in chamber temperature, chamber density and oxygen concentration and increases when the injection velocity is increased. It is observed that across the range of chamber conditions considered, the computed extinction scalar dissipation rates correlate well with the measured lift-off heights. When chamber temperatures and O_2 concentrations are varied, the results are found to be sensitive to the choice of the chemical kinetic mechanism.
机译：通过使用扩散火焰消光作为识别升空的标准，在柴油机中对火焰升空高度进行建模。结果表明，射流中化学计量的标量耗散率与计算的消光标量耗散率匹配的轴向距离与升空高度相关。研究了注入压力（40-138 MPa），腔室密度（14.8-58.5 kg / m〜3），腔室温度（1000-1300 K）和O_2摩尔浓度（10-21％）的影响。选择正庚烷作为柴油的替代物。采用两种化学动力学机理，一种37种，56步的机理和一种159种，1540步的机理。与实验结果一致，计算结果表明火焰剥离高度随腔室温度，腔室密度和氧气浓度的增加而降低，并随着注入速度的增加而增加。可以看出，在所考虑的腔室条件范围内，计算出的消光标量耗散率与测得的提离高度高度相关。当腔室温度和O_2浓度变化时，发现结果对化学动力学机制的选择很敏感。

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