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首页> 外文期刊>Combustion Science and Technology >Prediction of Flame Liftoff Height of Diffusion/Partially Premixed Jet Flames and Modeling of Mild Combustion Burners
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Prediction of Flame Liftoff Height of Diffusion/Partially Premixed Jet Flames and Modeling of Mild Combustion Burners

机译：扩散/部分预混射流火焰升空高度的预测和轻度燃烧器的建模

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In this article, a new flame extinction model based on the k/ε turbulence time scale concept is proposed to predict the flame liftoff heights over a wide range of coflow temperature and O_2 mass fraction of the coflow. The flame is assumed to be quenched, when the fluid time scale is less than the chemical time scale (Da < 1). The chemical time scale is derived as a function of temperature, oxidizer mass fraction, fuel dilution, velocity of the jet and fuel type. The present extinction model has been tested for a variety of conditions: (a) ambient coflow conditions (1 atm and 300 K) for propane, methane and hydrogen jet flames, (b) highly preheated coflow, and (c) high temperature and low oxidizer concentration coflow. Predicted flame liftoff heights of jet diffusion and partially premixed flames are in excellent agreement with the experimental data for all the simulated conditions and fuels. It is observed that flame stabilization occurs at a point near the stoichiometric mixture fraction surface, where the local flow velocity is equal to the local flame propagation speed. The present method is used to determine the chemical time scale for the conditions existing in the mild/ flameless combustion burners investigated by the authors earlier. This model has successfully predicted the initial premixing of the fuel with combustion products before the combustion reaction initiates. It has been inferred from these numerical simulations that fuel injection is followed by intense premixing with hot combustion products in the primary zone and combustion reaction follows
机译：本文提出了一种基于k /ε湍流时间尺度概念的新的熄火模型，以预测在宽的同流温度和同流的O_2质量分数范围内的火焰上升高度。当流体时间标度小于化学时间标度（Da <1）时，假定火焰已熄灭。化学时间标度是温度，氧化剂质量分数，燃料稀释度，喷射速度和燃料类型的函数。本消光模型已经在多种条件下进行了测试：（a）丙烷，甲烷和氢气喷射火焰的环境同流条件（1 atm和300 K），（b）高度预热的同流，以及（c）高温和低温氧化剂浓度同流。射流扩散和部分预混火焰的预测火焰起升高度与所有模拟条件和燃料的实验数据高度吻合。可以观察到，火焰稳定发生在化学计量混合物分数表面附近，该处的局部流速等于局部火焰的传播速度。本方法用于确定作者较早研究的温和/无焰燃烧器中存在的条件的化学时间标度。该模型已经成功地预测了在燃烧反应开始之前燃料与燃烧产物的初始预混合。从这些数值模拟可以推断出，在燃料喷射之后，在主要区域中与热燃烧产物进行强烈的预混合，然后发生燃烧反应。

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