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Propagation and extinction of subatmospheric counterflow methane flames

机译：低于大气的逆流甲烷火焰的传播和消灭

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摘要

Measurements of flame propagation velocities and extinction states in counterflow provide a valuable source of flame data that contain information about fundamental combustion physics. The approach to properly account for stretch effects in counterflow flame measurements through non-intrusive laser-based local velocity characterization was advanced in the mid-80s by Law and coworkers at atmospheric conditions with simple fuels. Subsequently, several research groups have extended the measurements to elevated pressures and complex fuels. However, counterflow flame data at subatmospheric pressures are limited. In the present study, a method is introduced for measuring laminar flame speeds and extinction strain rates in subatmospheric counterflow flames. A numerical study was performed to assess the dynamics of tracer particles used to facilitate measurements. It was found that the particle phase dynamics used in particle velocimetry measurements are not always representative of the underlying gas phase motion due to thermophoresis and insufficient drag, especially at low pressures. A numerical scheme was implemented whereby the computed particle phases were used for proper comparison with measurements and, based on the computed results, to infer the corresponding values of the gas phase. The method was applied to premixed methane/air and non-premixed methane–nitrogen/oxygen flames at pressures as low as 0.1 atm. Complimentary flame structure simulations were carried out which show that the kinetics of formyl radical prompt dissociation strongly impact the computed subatmospheric flames and may influence the validation of unimolecular and bimolecular reactions rate constants when tested against laminar flame data.
机译：逆流中火焰传播速度和熄灭状态的测量提供了有价值的火焰数据源，其中包含有关基本燃烧物理学的信息。 Law和同事在80年代中期提出了在大气条件下使用简单燃料通过非侵入性基于激光的局部速度表征来适当解决逆流火焰测量中拉伸效应的方法。随后，几个研究小组将测量范围扩大到高压和复杂燃料。但是，低于大气压的逆流火焰数据是有限的。在本研究中，介绍了一种用于测量低于大气逆流火焰的层流火焰速度和消光应变率的方法。进行了数值研究，以评估用于促进测量的示踪剂颗粒的动力学。已经发现，由于热泳和阻力不足，尤其是在低压下，在颗粒测速测量中使用的颗粒相动力学并不总是代表潜在的气相运动。实施了一种数值方案，其中将计算出的颗粒相用于与测量值进行适当比较，并基于计算出的结果推断出气相的相应值。该方法适用于压力低至0.1atm的预混合甲烷/空气和非预混合甲烷-氮气/氧气火焰。进行了免费的火焰结构模拟，结果表明，对层流火焰数据进行测试时，甲酰基自由基迅速解离的动力学强烈影响所计算的低于大气压的火焰，并且可能会影响单分子和双分子反应速率常数的验证。

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