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Rate-ratio asymptotic analysis of the influence of addition of carbon monoxide on the structure and mechanisms of extinction of nonpremixed methane flames with comparison to experiments

机译：一氧化碳的添加对非预混甲烷火焰结构和熄灭机理影响的速率比渐近分析

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摘要

Rate -ratio asymptotic (RRA) analysis is carried out to elucidate the influence of carbon monoxide on the structure and critical conditions of extinction of nonpremixed methane flames. Steady, axisymmetric, laminar flow of two counterflowing streams toward a stagnation plane is considered. One stream, called the fuel stream is made up of a mixture of methane (CH4) and nitrogen (N-2). The other stream, called the oxidizer stream, is a mixture of oxygen (O-2), and N-2. Carbon monoxide (CO) is added either to the oxidizer stream or to the fuel stream. Chemical reactions, represented by four global steps, are presumed to take place in a thin reaction zone. To the leading order the reactants, CH4, O-2, and CO are completely consumed in the reaction zone. On either side of this thin reaction zone, the flow field is inert These inert regions represent the outer structure of the flame. The outer structures provide matching conditions required for predicting the structure of the reaction zone. In the reaction zone, chemical reactions are presumed to take place in two layers the inner layer and the oxidation layer. The scalar dissipation rate at extinction is predicted from results of the asymptotic analysis and compared with previous measurements and computational predictions using detailed chemistry. The predictions of the asymptotic analysis are found to agree well with the experimental data for CO addition to the fuel stream, and for small amounts of CO addition to the oxidizer stream. For large amounts of CO addition to the oxidizer stream, the approximations introduced in the asymptotic analysis become inaccurate. A key finding is that with increasing amounts of CO added to the oxidizer stream the scalar dissipation rate at extinction first increases and then decreases. It is attributed to changes in location of the inner layer within the reaction zone. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：进行了速率比渐近分析（RRA），以阐明一氧化碳对未预混甲烷火焰熄灭的结构和临界条件的影响。考虑到两个滞流向停滞平面的稳定，轴对称，层流。一种称为燃料流的流由甲烷（CH4）和氮（N-2）的混合物组成。另一流称为氧化剂流，是氧气（O-2）和N-2的混合物。一氧化碳（CO）添加到氧化剂流或燃料流中。假定以四个全局步骤表示的化学反应发生在稀薄的反应区中。首先，反应物CH4，O-2和CO在反应区中被完全消耗掉。在稀薄反应区的两侧，流场是惰性的。这些惰性区域代表火焰的外部结构。外部结构提供了预测反应区结构所需的匹配条件。在反应区中，假定化学反应在两层内层和氧化层中发生。根据渐近分析的结果预测熄灭时的标量耗散率，并与先前的测量结果和使用详细化学方法的计算预测进行比较。发现渐近分析的预测与将CO添加到燃料流中以及少量CO添加到氧化剂流中的实验数据非常吻合。对于将大量的CO添加到氧化剂物流中，渐进分析中引入的近似值变得不准确。一个关键发现是，随着添加到氧化剂流中的CO数量的增加，熄灭时的标量耗散率首先增加，然后降低。这归因于内层在反应区内的位置变化。 （C）2016年燃烧研究所。由Elsevier Inc.出版。保留所有权利。

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