Study On Characteristics And Dynamics Of Hydrogen Enriched Fuel/Air Premixed Flame Propagation In Closed Duct

Nowadays,the traditional fossil fuel has been complained for causing some environmental problems.People initiated to find some kinds of clean and efficient fuel to replace it.Hydrogen is one kind of potential energy,but it has not been popularized for its high manufacturing cost.Then the hydrogen enriched fuel came into view.However,as a kind of flammable gas,it can be ignited easily by accident and cause serious fire disasters.Thus,the safe utilization of hydrogen enriched fuel should be seriously concerned.In some narrow confined space,such as ducts,underground corridors,municipal pipe networks and corridors,once the flammable gas was mixed with air,forming the flammable premixed gas,it can be ignited easily by some ignition sources such as fire,electric spark and hot surface,which would cause serious casualties and property damage.However,few relative researches on the hydrogen enriched fuel have been done,which was unfavorable for the safe utilization of the hydrogen enriched fuel.Thus,in this paper,the experiments were conducted in the closed rectangle duct which was regarded as the narrow confined space to discuss the flame propagation of hydrogen enriched fuel-air premixed flame with different hydrogen content,inhibitor content and equivalent ratio.During the experiments,two visual windows were set on the sidewall of the duct so that the flame shapes could be recorded by the Schlieren system and high-speed camera.A pressure sensor was placed near the right end of the duct for collecting overpressure data.By combining the data acquired in various experimental conditions,the flame propagation process and its dynamics were discussed.The results showed that with the equivalent ratio of syngas approaching 1.0 and the hydrogen content increasing,the flame shape presented more drastic changes and the flame propagation speed and overpressure increased.Moreover,the influence of equivalent ratio on the flame propagation speed was more obvious than that on overpressure.With the inhibition of N2 or CO2,the flame shape changed more stably and the flame propagation speed and overpressure decreased.Moreover,CO2 presented more outstanding inhibiting effect.The reduced flame tip position was calculated by Bychkov’s model.The calculated data was compared with the experimental data,pointing out that the change of equivalent ratio,inhibitor content,kind of fuel or kind of inhibitor would influence the accuracy of Bychkov’s model and the influence of hydrogen content was much slighter.The meeting moments and positions of pressure wave and flame front were calculated,which proved that the pressure wave can affect the flame shape changes but it is not the key factor for tulip flame formation.The Froude number was listed to quantize the influence of buoyancy effect.By analyzing the Lewis number and flame thickness calculated,the flame instability was proved to be influenced by the changing of equivalent ratio,inhibitor content and hydrogen content.The inhibiting mechanism of N2 or CO2 was discussed on both thermal and kinetics aspects,which also explained the more outstanding inhibiting effect of CO2.