回流与火焰拉伸对氢气微尺度燃烧的影响

Impact of backward flow and reaction stretch on combustion stability of hydrogen/air mixture in a micro-combustor

对火道内置有钝体的微型燃烧器开展了数值模拟研究,以探讨阻塞比(0.3~0.8)对微型钝体燃烧器中氢气/空气混合物燃烧稳定性的影响.采用文献中实验数据验证了所采用的数值模型的准确性,模拟结果表明:氢气/空气混合物的熄火极限随着阻塞比增大而呈先增后减的非单调变化趋势.当阻塞比为0.5时,熄火极限可达最高值,即38m/s.主要原因是增大的阻塞比虽能产生更大的回流区,有利于稳焰,但同时也使钝体附近的速度梯度增大,引起了更强的流体剪切力和反应区拉伸,不利于稳定燃烧.

The numerical simulations of a micro-combustor with a bluff body were carried out.The objective is to investigate the impact of blockage ratio(0.3~0.8)on the combustion stability of hydrogen/air mixture in this combustor.Experimental data in the literature were used to validate the models.The results show that the extinction limit of hydrogen/air mixture increases first and then decreases nonmonotonically with the increase of blockage ratio.When the blockage ratio is 0.5,the maximum extinguishing limit is 38 m/s.The main reason behind is then discussed.The increase of blocking ratio can produce larger reflux zone,which is beneficial to flame stabilization.However,the increase of blocking ratio also increases the velocity gradient near the bluff body,resulting in a stronger fluid shear force and stretch of reaction zone,which is not negative to combustion stabilization.