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首页> 外文期刊>Combustion and Flame >The role of differential diffusion during early flame kernel development under engine conditions - part Ⅱ: Effect of flame structure and geometry
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The role of differential diffusion during early flame kernel development under engine conditions - part Ⅱ: Effect of flame structure and geometry

机译：发动机条件下早期火焰内核开发期间差分扩散的作用 - 第Ⅱ部分：火焰结构与几何的影响

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From experimental spark ignition (SI) engine studies, it is known that the slow-down of early flame kernel development caused by the (Le 1)-property of common transportation-fuel/air mixtures tends to increase cycle-to-cycle variations (CCV). To improve the fundamental understanding of the complex phenomena inside the flame structure of developing flame kernels, an engine-relevant DNS database is investigated in this work. Conclusive analyses are enabled by considering equivalent flame kernels and turbulent planar flames computed with Le 1 and Le = 1. In Part I of the present study (Falkenstein et al., Combust. Flame, 2020), a reduced representation of the local mixture state was proposed for the purpose of this analysis. Fluctuations in heat release rate attributed to differential diffusion were found to be governed by the parameters local enthalpy, local equivalence ratio, and H-radical mass fraction. Here, a coupling relation for the diffusion-controlled mixture parameter local enthalpy with local flame geometry and structure is derived, characterized by the key parameters k and vertical bar del c vertical bar/vertical bar del c vertical bar(lam). The analysis shows that the large positive global mean curvature intrinsic to the flame kernel configuration may detrimentally affect the local mixture state inside the reaction zone, particularly during the initial flame kernel development phase. External energy supply by spark ignition may effectively bridge over this critical stage, which causes the impact of global mean flame kernel curvature to be small under the present conditions compared to the overall effect of Le not equal 1 observed in a statistically planar flame. Once ignition effects have decayed, the mixture state inside the reaction zone locally exhibits an identical dependence on vertical bar del c vertical bar as in a strained laminar flame. This implies that differential diffusion effects at Karlovitz numbers representative for part-load conditions are not weakened by small-scale turbulent mixing, which is undesirable for the engine application, but can be favorable in terms of modeling. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：从实验火花点火（SI）发动机研究中，众所周知，由（LE> 1）引起的普通运输 - 燃料/空气混合物引起的早期火焰核开发的缓慢趋于增加循环到循环变化（CCV）。为了改善对发育火焰核的火焰结构内复杂现象的基本理解，在这项工作中调查了发动机相关的DNS数据库。通过考虑用Le> 1和Le = 1计算的等效火焰核和湍流平面火焰来实现结论性分析。在本研究的第I部分（Falkenstein等，燃烧。火焰，2020），局部混合物的减少表示出于该分析的目的提出了国家。发现归因于差分扩散的热释放率的波动被参数局部焓，局部等效比和H自由基质量分数。这里，推导出与局部火焰几何和结构的扩散控制混合参数局部焓的耦合关系，其特征在于键参数k和垂直条德尔C垂直条/垂直条德尔C垂直条（LAM）。分析表明，火焰核构型的大阳性全局平均曲率固有可能不利地影响反应区内的局部混合物状态，特别是在初始火焰核开发阶段。通过火花点火的外部能量供应可以有效地桥接在这种关键阶段上，这导致全局平均火焰核曲率在当前条件下较小，而在统计平面火焰中观察到的LE不等于1的整体效果相比。一旦点火效果腐烂，反应区内的混合物状态就会在紧张的层状火焰中显示出对垂直条德尔C垂直杆的相同依赖性。这意味着通过小规模湍流混合的小规模湍流混合，KARLOVITZ数量代表的差分扩散效应不会削弱，这对于发动机应用是不希望的，但在建模方面可能是有利的。 （c）2020燃烧研究所。由elsevier Inc.出版的所有权利保留。

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