| Mixing a certain proportion of hydrogen into the natural gas pipeline network is an effective way to solve the problem of hydrogen economic transportation.However,affected by the physical and chemical properties of hydrogen,this transportation method will have a great impact on the safety of the pipeline network.In addition,the special geometrical structure in the gas pipeline,such as obstacles,elbows and bifurcations,will also affect the explosion characteristics of the mixed gas.Therefore,based on the self-built experimental platform and combined with RANS simulation,this paper explores the effects of hydrogen addition and the obstacle position on the combustion and explosion characteristics of methane-hydrogen-air premixed gas in the straight pipe,90 °bend and T-shaped bifurcation pipe.The research results are of great significance for formulating corresponding measures for fire prevention or disaster reduction and the safety development of mixed hydrogen and hydrocarbon gas.(1)Influence of hydrogen addition on combustion and explosion characteristics of methane-hydrogen-air mixture in three types of pipes:The volume fraction of hydrogen in the methane/hydrogen mixture with a small amount of hydrogen has a significant effect on the combustion and explosion characteristics of the mixture The flame propagation velocity,the maximum explosion overpressure and the strain of the pipe wall increased with the increase of the hydrogen concentration,and when the hydrogen concentration was greater than 10%,the enhancement effect of hydrogen addition on the combustion and explosion reaction was more significant.The T-shaped bifurcation structure and 90 °elbow have little influence on the explosion characteristics in the upstream pipe of the bifurcation and elbow,but have a great influence on the downstream pipe.When the flame entered the bifurcation and elbow,the flame propagation velocity and maximum explosion overpressure decreased rapidly.After the flame passed through the bifurcation and elbow,due to the disturbance of the pipe structure and the coupling of multi-wave system,the turbulence intensity in the pipe increased rapidly,and the flame propagation velocity and explosion overpressure rebounded rapidly.The 90 °elbow and T-shaped bifurcation structure can enhance the combustion and explosion reaction,in which the strengthening effect of 90 °elbow is the most significant,followed by T-shaped bifurcated pipe.When the hydrogen concentration is 20%,the maximum flame propagation velocity in the unobstructed 90 °bend is 179.31m/s,which is 46.23% higher than that of the straight pipe and 8.52% higher than that of the T-shaped bifurcated pipe,and the maximum explosion pressure is 0.555 MPa,which was 31.83%higher than that of the straight pipe and 3.16% higher than that of the Tshaped bifurcation pipe.(2)Influence of obstacle position on combustion and explosion characteristics of methane-hydrogen-air mixture in three types of pipes:Obstacles have a significant influence on the combustion and explosion characteristics of the mixed gas.Compared with the pipeline without obstacles,the maximum flame propagation velocity in the barrier pipe increases nearly three times and The maximum explosion pressure increases nearly two times.Moreover,the synergistic effect of obstacles and the addition of hydrogen can significantly enhance the explosion intensity of the mixed gas,in which the strengthening effect in the 90 °bend is the most significant,followed by the T-shaped bifurcated pipe.In addition,under the influence of the turbulent vortex near the obstacle,the flame in the pipe was obviously distorted when it approached the obstacle,which enhanced the flame instability and accelerated the transition of the flame from laminar to turbulence.The explosion intensity of methane-hydrogen-air mixture in the curved pipe can be divided into two parts according to the obstacle position.When the distance between the obstacle and the elbow was more than 6 times the pipe diameter,the maximum explosion pressure was mainly affected by the position of the obstacle,and when the distance between the obstacle and the elbow was less than 6 times the pipe diameter,the maximum explosion pressure is affected by the combustion characteristics of the mixed gas and the obstacle position.The relative position of the obstacle and the bifurcation in the T-shaped bifurcation tube has an obvious influence on the ignition and explosion characteristics of the mixed gas.when the obstacle was located before the bifurcation,the explosion intensity was more sensitive to the hydrogen concentration,and the synergistic effect of the obstacle position and the hydrogen addition was beneficial to increase the explosion intensity in the two pipes.When the obstacle was located behind the bifurcation,the explosion characteristic of the mixed gas was less sensitive to the hydrogen concentration,and the position effect of the obstacle had little effect on the explosion intensity in the T2 branch pipe.At this time,the hydrogen concentration play a leading role in the explosion intensity in the branch T2. |
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