Hydrogen, Methane, Ethylene and Propylene Blending on the Ignition Delay Time of n-Heptane/Toluene Mixtures under Homogeneous and Nonpremixed Counterflowing Conditions
Hydrogen, Methane, Ethylene and Propylene Blending on the Ignition Delay Time of n-Heptane/Toluene Mixtures under Homogeneous and Nonpremixed Counterflowing Conditions
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均相非预混逆流条件下氢气、甲烷、乙烯和丙烯共混对正庚烷/甲苯混合物点火延迟时间的影响
DOI：
10.1080/00102202.2019.1675050
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发表时间：
2019
影响因子：
1.9
通讯作者：
Zhang Hai
中科院分区：
文献类型：
--
作者：
Shen Wenfeng;Zhang Yang;Yang Xiehe;Zhang Hai
在均相和非预混逆流条件下，数值研究了氢气（H2）、甲烷（CH4）、乙烯（C2H4）和丙烯（C3H6）共混对正庚烷/甲苯混合物着火延迟时间的影响。在这两种配置中，结果表明，H2和C2H4的添加有利于促进点火，而CH4和C3H6的添加则抑制大气压下的点火。 H2、CH4和C2H4在高压下的混合效果与大气压下相似。然而，C3H6的抑制作用在较高压力下变弱。相同摩尔共混比下，在均相体系中，C2H4共混比H2共混具有更强的促进作用，但在非预混逆流构型中，结果相反。轻质气体混合的效果几乎不是由热物理性质的变化引起的；相反，它以化学动力学的变化为主，包括主要吸热支化反应、主要产热反应和自由基形成反应速率的变化。此外，对于均相混合物，H2加成直接增强主要支化反应H + O2<=> O + OH，而C2H4加成直接增强主要放热反应C2H4+ OH <=> C2H3+ H2O。 CH4加成消耗OH并产生CH3以抑制点火。 C3H6加成会消耗H和OH来抑制点火。拉伸非预混火焰的点火从高温氧化剂侧开始。由于H2的质量扩散性较强，混合H2比混合C2H4以更高的温度渗透到氧化剂侧。少量的 H2 混合会产生更高的 H、OH、CH3 自由基，更高的热产物速率，从而比 C2H4 混合更短的点火延迟时间。该效应随着应变率的增加而增强。此外，结果表明，点火延迟时间仅对外部添加的轻质气体组分的分子输运敏感，而不对燃料分解产生的气体分子的分子输运敏感。
Effects of hydrogen (H2), methane (CH4), ethylene (C2H4) and propylene (C3H6) blending on the ignition delay time ofn-heptane/toluene mixtures were numerically studied under both homogeneous and nonpremixed counterflowing conditions. In both configurations, results reveal that the addition of H2and C2H4is beneficial to promote ignition, while the addition of CH4and C3H6inhibits ignition at atmospheric pressure. The blending effects of H2, CH4and C2H4at elevated pressures are similar to that at atmospheric pressure. However, the inhibiting effect of C3H6becomes weaker under higher pressures. At the same mole blending ratio, in a homogeneous system, C2H4blending has stronger promotion effect than H2blending, but in the nonpremixed counterflowing configuration, the results are opposite. The effect of light gas blending is barely caused by the changes of the thermophysical properties; instead, it is dominated by the changes of chemical kinetics, including the changes of the rates of the main endothermal branching reactions, main heat production reactions, and the radical formation reactions. Furthermore, for the homogeneous mixtures, H2addition directly enhances the main branching reaction H + O2<=> O + OH, while C2H4addition directly enhances the main exothermic reactions C2H4+ OH <=> C2H3+ H2O. CH4addition consumes OH and produces CH3to inhibit ignition. C3H6addition consumes H and OH to inhibit ignition. The ignition of a stretched nonpremixed flame begins on the high-temperature oxidizer side. Due to the stronger mass diffusivity of H2, the blended H2permeates to the oxidizer side with a higher temperature than the blended C2H4does. A small amount of H2blending results in much higher H, OH, CH3radicals, higher heat product rate, and thereby shorter ignition delay time than the C2H4blending. The effect is enhanced with increasing strain rate. In addition, the results reveal that the ignition delay time is only sensitive to the molecular transport of the externally-added light gas components, rather than that of the gas molecules generated by the fuel decomposition.