Numerical experiments on reaction front propagation in n-heptane/air mixture with temperature gradient
Numerical experiments on reaction front propagation in n-heptane/air mixture with temperature gradient
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DOI：
10.1016/j.proci.2014.06.102
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
P. Dai;Zheng Chen;Shiyi Chen;Y. Ju
中科院分区：
文献类型：
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作者：
P. Dai;Zheng Chen;Shiyi Chen;Y. Ju
通常，不同的自燃模式可以产生一个热点，其中点火发生早于周围的混合物。然而，对于具有负温度系数（NTC）行为的大碳氢燃料，当温度在NTC区域内时，在较低温度下比在较高温度下点火更早发生。因此，冷点也可能导致不同的自燃模式。在本研究中，数值研究了在NTC区域内和低于NTC区域的初始温度下，正庚烷/空气混合物在一维平面构型中由温度梯度引起的反应前沿传播模式。首次识别了由正温度梯度冷斑引起的不同超声速自燃模式。研究发现，初始温度梯度对自燃模式有很大的影响。随着冷斑正温度梯度的增大，依次观察到超声速自燃爆燃、爆轰、激波-爆轰、激波-爆燃。结果表明，在爆燃波和激波之间的混合气的冲击压缩产生了一个附加的点火核，它决定了自燃模式。此外，冷点与温度低于NTC制度的热点进行了比较。对于热点和冷点观察到类似的自燃模式。不同的自燃模式在考虑简化配置的归一化温度梯度和声激励时间尺度比方面进行了总结。结果表明，不同的自燃模式之间的过渡是没有很大的影响的NTC行为。因此，我们的1-D模拟表明，像热点，冷点也可能产生爆震在发动机时，使用的燃料与NTC行为和温度是在NTC制度。
Usually different autoignition modes can be generated by a hot spot in which ignition occurs earlier than that in the surrounding mixture. However, for large hydrocarbon fuels with negative temperature coefficient (NTC) behavior, ignition happens earlier at lower temperature than that at higher temperature when the temperature is within the NTC regime. Consequently, a cool spot may also result in different autoignition modes. In this study, the modes of reaction front propagation caused by temperature gradient in a one dimensional planar configuration are investigated numerically forn-heptane/air mixture at initial temperature within and below the NTC regime. For the first time, different supersonic autoignition modes caused by a cool spot with positive temperature gradient are identified. It is found that the initial temperature gradient has strong impact on autoignition modes. With the increase of the positive temperature gradient of the cool spot, supersonic autoignitive deflagration, detonation, shock-detonation, and shock-deflagration are sequentially observed. It is found that shock compression of the mixture between the deflagration wave and leading shock wave produces an additional ignition kernel, which determines the autoignition modes. Furthermore, the cool spot is compared with the hot spot with temperature below the NTC regime. Similar autoignition modes are observed for the hot and cool spots. Different autoignition modes in the considered simplified configuration are summarized in terms of the normalized temperature gradient and acoustic-to-excitation time scale ratio. It is shown that the transition between different autoignition modes is not greatly affected by the NTC behavior. Therefore, our 1-D simulation indicates that like hot spot, the cool spot may also generate knock in engines when fuels with NTC behavior is used and the temperature is within the NTC regime.