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首页> 外文期刊>Combustion and Flame >Numerical and experimental study of soot formation in laminar diffusion flames burning simulated biogas fuels at elevated pressures
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Numerical and experimental study of soot formation in laminar diffusion flames burning simulated biogas fuels at elevated pressures

机译：在高压下燃烧模拟沼气燃料的层流扩散火焰中烟灰形成的数值和实验研究

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摘要

The effects of pressure and composition on the sooting characteristics and flame structure of laminar diffusion flames were investigated. Flames with pure methane and two different methane-based, bio-gas-like fuels were examined using both experimental and numerical techniques over pressures ranging from 1 to 20 atm. The two simulated biogases were mixtures of methane and carbon dioxide with either 20% or 40% carbon dioxide by volume. In all cases, the methane flow rate was held constant at 0.55 mg/s to enable a fair comparison of sooting characteristics. Measurements for the soot volume fraction and temperature within the flame envelope were obtained using the spectral soot emission technique. Computations were performed by solving the unmodified and fully-coupled equations governing reactive, compressible flows, which included complex chemistry, detailed radiation heat transfer and soot formation/oxidation. Overall, the numerical simulations correctly predicted many of the observed trends with pressure and fuel composition. For all of the fuels, increasing pressure caused the flames to narrow and soot concentrations to increase while flame height remained unaltered. All fuels exhibited a similar power-law dependence of the maximum carbon conversion on pressure that weakened as pressure was increased. Adding carbon dioxide to the methane fuel stream did not significantly effect the shape of the flame at any pressure; although, dilution decreased the diameter slightly at 1 atm. Dilution suppressed soot formation at all pressures considered, and this suppression effect varied linearly with CO_2 concentration. The suppression effect was also larger at lower pressures. This observed linear relationship between soot suppression and the amount of CO_2 dilution was largely attributed to the effects of dilution on chemical reaction rates, since the predicted maximum magnitudes of soot production and oxidation also varied linearly with dilution.
机译：研究了压力和组成对层流扩散火焰的烟ot特性和火焰结构的影响。在1至20 atm的压力范围内，使用实验和数值技术对纯甲烷和两种不同的甲烷类生物气燃料进行了火焰测试。两种模拟沼气是甲烷和二氧化碳与20％或40％体积二氧化碳的混合物。在所有情况下，甲烷流速均保持恒定在0.55 mg / s，以实现烟comparison特性的合理比较。使用光谱烟灰发射技术获得了火焰包络内烟灰体积分数和温度的测量值。通过求解控制反应性可压缩流的未修正且完全耦合的方程式进行计算，该方程式包括复杂的化学反应，详细的辐射热传递和烟灰形成/氧化。总体而言，数值模拟正确地预测了许多观察到的有关压力和燃料成分的趋势。对于所有燃料，压力的增加导致火焰变窄，烟尘浓度增加，而火焰高度保持不变。所有燃料均表现出最大碳转化率与压力的幂律相关性，随着压力的增加，碳的转化率逐渐减弱。在任何压力下，将二氧化碳添加到甲烷燃料流中均不会显着影响火焰的形状。尽管稀释在1 atm时使直径稍微减小。在所有考虑的压力下，稀释都会抑制烟灰的形成，并且这种抑制效果随CO_2浓度线性变化。在较低压力下抑制效果也更大。观察到的烟灰抑制与CO_2稀释量之间的线性关系很大程度上归因于稀释对化学反应速率的影响，因为预计的烟灰生成和氧化的最大幅度也随稀释而线性变化。

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