Experimental and Numerical Investigation of Flow Field and Soot Particle Size Distribution of Methane-Containing Gas Mixtures in a Swirling Burner

The formation of
soot in a swirling flow is investigated experimentally
and numerically in the context of biogas combustion using a CO2-diluted methane/oxygen flame. Visualization of the swirling
flow field and characterization of the burner geometry is obtained
through PIV measurements. The soot particle size distributions under
different fuel concentrations and swirling conditions are measured,
revealing an overall reduction of soot concentration and smaller particle
sizes with increasing swirling intensities and leaner flames. An axisymmetric
two-dimensional CFD model, including a detailed combustion reaction
mechanism and soot formation submodel, was implemented using a commercial
computational fluid dynamics (CFD) code (Ansys Fluent). The results
are compared with the experiments, with similar trends observed for
the soot size distribution under fuel-lean conditions. However, the
model is not accurate enough to capture soot formation in fuel-rich
combustion cases. In general, soot particle sizes from the model are
much smaller than those observed in the experiments, with possible
reasons being the inappropriate modeling in Fluent of governing mechanisms
for soot agglomeration, growth, and oxidation for CH4-CO2 mixtures.

本研究针对掺二氧化碳稀释的甲烷-氧气火焰开展沼气燃烧场景下旋流流场中炭黑（soot）生成过程的实验与数值模拟研究。通过粒子图像测速法（Particle Image Velocimetry，PIV）获取旋流流场可视化结果与燃烧器几何特性表征数据。测试不同燃料浓度与旋流工况下的炭黑粒径分布，结果表明：随着旋流强度提升与火焰贫燃化程度加深，炭黑总体浓度呈下降趋势，且粒径更小。本研究借助商用计算流体动力学（Computational Fluid Dynamics，CFD）软件（Ansys Fluent），搭建了包含详细燃烧反应机理与炭黑生成子模型的轴对称二维CFD模型。将数值模拟结果与实验数据对比后发现，贫燃工况下的炭黑粒径分布变化趋势与实验结果一致。但该模型无法准确复现富燃燃烧工况下的炭黑生成过程。总体而言，数值模拟得到的炭黑粒径远小于实验观测值，其潜在原因为：Ansys Fluent中针对CH4-CO2混合燃料的炭黑团聚、生长与氧化主控机制的建模方式存在不当之处。