定容燃烧弹内含煤尘甲烷爆燃火焰传播特性试验研究

Experimental study on propagation characteristics of the deflagration flame of coal dust/methane/air in constant volume chamber

为探究煤尘对甲烷爆燃火焰的直观影响,在定容燃烧弹(Constant Volume Chamber,CVC)内利用激光纹影技术获取了甲烷球形火焰纹影图像及含煤尘甲烷火焰纹影图像,分析了不同体积分数甲烷火焰(6.5%、8.0%、9.5%)的不稳定性,对比了不同质量浓度煤尘(5 g/m^(3)、10 g/m^(3)、15 g/m^(3)、20 g/m^(3)、25 g/m^(3))对甲烷火焰的影响,分析了含煤尘甲烷火焰传播机理。结果表明,定容燃烧弹内球形火焰发展经历了层流火焰、胞状不稳定火焰。煤尘对甲烷火焰的影响呈明显的阶段特性:在层流燃烧阶段,煤尘因吸热抑制火焰传播,且煤尘质量浓度越高,抑制作用越强;散布的煤尘可对火焰锋面产生扰动,使火焰加快发展为胞状不稳定火焰,且甲烷体积分数越接近化学当量比,煤尘质量浓度越高,火焰可更快发展为胞状不稳定火焰;随着化学反应速率提高,火焰温度上升,煤焦开始参与反应并增强流场自发光及反应持续时间。

To study the visual impact of coal dust on the methane deflagration flame, the spherical flame schlieren photographs of methane and methane-coal dust flame schlieren photographs were obtained by laser schlieren technology in a Constant Volume Chamber(CVC). The instability of methane flame with different volume fractions(6.5%, 8.0%, 9.5%) was analyzed, the effects of coal dust with different mass concentrations(5 g/m~3, 10 g/m~3, 15 g/m~3, 20 g/m~3, 25 g/m~3) on methane flame were compared, and the propagation mechanism of methane-coal dust flame was analyzed. The experimental results show that the spherical flame in the CVC develops through the laminar flame and cellular unstable flame. The lower the methane volume fraction and the higher the coal dust mass concentration, the flame is more likely to be floated by buoyancy instability. The influence of coal dust on methane flame has obvious stage characteristics: in the laminar combustion stage, coal dust inhibits flame propagation by reducing the rate of chemical reactions due to endothermic, and the higher the concentration of coal dust, the stronger the inhibition effect, which is reflected in the same moment of the schlieren photographs, the higher the mass concentration of coal dust, the smaller the radius of the spherical flame;The dispersed coal dust can disturb the flame front and accelerate the flame to develop into cellular unstable flame. The closer the methane volume fraction is to the stoichiometric ratio, and the higher the coal dust concentration, the faster the flame can develop into a cellular unstable flame, which is reflected in the same moment of the schlieren photographs. The higher the coal dust mass concentration is, the more dense the flame front cells are;As the cellular unstable flame is fully developed, the chemical reaction rate increases, the flame temperature increases, the coal coke starts to participate in the reaction, the self-illumination and reaction duration of the flow field is enhanced.