平行杆束对氢气/空气预混火焰的阻火特性研究

Study on the quenching characteristics of parallel rods on premixed hydrogen-air flame

研究了一种新型阻火元件--平行杆束对不同当量比的氢气/空气预混火焰的阻火特性。采用高速纹影系统来记录火焰演变过程,并根据拍摄的纹影图像计算出火焰前锋速度;在平行杆束前后安装了压力传感器来记录爆炸压力。结果表明,氢气/空气预混气体的当量比和初始压力会对火焰形态、火焰速度和爆炸压力产生影响,从而影响火焰的淬熄行为。试验观察到四种火焰发展模式:淬熄、临界淬熄、临界通过和通过。临界淬熄和临界通过模式在下游管道均观察到明显的气流,临界通过模式中气流重新燃烧发生爆炸导致阻火失败。当阻火成功时,平行杆束对火焰速度和爆炸压力具有明显的抑制效果并且可以有效衰减压力波;当阻火失败时,平行杆束增加火焰速度的倍数随着当量比的增加呈现“M”形变化趋势,速度比在当量比为1时为极小值。临界阻火速度在当量比为1时最大,临界最大爆炸压力在贫氢阶段保持不变,在富氢阶段随当量比增大而增大。临界初始压力在当量比为1时最小,此时阻火最困难。

An experimental study was carried out on the effect of different initial pressures and equivalent ratios on the quenching of hydrogen-air-premixed flames by parallel rods.High-speed schlieren photography was used to record the flame evolution.The flame tip speed was calculated according to the flame evolution images.Two pressure sensors were mounted upstream and downstream of the parallel rods to detect the explosion pressure.The results show that the flame propagation,explosion pressure,and flame quenching are affected by the hydrogen equivalent ratio and initial pressure.Four modes of flame propagation were observed,such as“quench”,“critical quench”,“critical pass”and“pass”.Significant gas flow was observed in the downstream pipe in both modes of“critical quench”and“critical pass”.The gas flow reignited and exploded in the mode of a“critical pass”.The“raised flame”appears at the wall of the upstream pipe and has a more significant speed than the central flame.The upper“raised flame”is more obvious than the lower“raised flame”.When the equivalent ratio is 1.25,the maximum flame tip speed and peak explosion pressure are found in the upstream pipe.Higher initial pressure increases the effect of the equivalent ratio on flame tip speed and explosion pressure.When the quenching is successful,the parallel rods have a significant suppression effect on the flame speed and explosion pressure,and can effectively absorb pressure waves.When the quenching is unsuccessful,the parallel rods have an accelerating effect on the flame in the downstream pipe and increase the explosion pressure.The multiples of flame speed accelerated by parallel rods show an“M”shape with the increase of the equivalent ratio.The speed ratio for flame acceleration is minimal for the equivalent ratio of 1.As the equivalent ratio increases,the critical quenching speed first increases and then decreases,reaching a maximum value for the equivalent ratio of 1.The maximum critical explosion pressure remains constant for various equivalence ratios at the lean hydrogen stage and increases with the increase of the equivalent ratio for the rich hydrogen.The critical initial pressure shows a“U”shape with an increasing equivalent ratio and is the lowest at the equivalent ratio of 1.The effect of the hydrogen equivalent ratio on flame quenching is more significant at the stage of lean hydrogen than at the stage of rich hydrogen.