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