Experimental study on unsteady dynamic propagation characteristics of biomass pyrolysis gas/air premixed explosion
In this paper,a vertically placed transparent round tube test platform was built.By changing the equivalent ratio and CH4 volume fraction,flame images and overpressure curves collected by high-speed cameras and overpressure sensors were collected,and factors such as flame structure,flame propagation process,overpressure curve,and overpressure oscillation were compared and explored.In this paper,the unsteady dynamic propagation characteristics of biomass pyrolysis gas exploded in a transparent tube were studied.The equivalent ratio ranges from 0.6 to 1.2,and the volume fraction of CH4 ranges from 30％to 70％.The results show that with the change in working conditions,the flame presents different propagation states,and the corresponding overpressure curves of the flame are also different.In this paper,three different flame propagation states are found,namely,the flame propagation state with only primary instability,the flame propagation state with both primary and secondary instability,and the flame propagation state with only secondary instability.Besides,it is found that the critical SL of biomass pyrolysis gas is around 40.30 cm/s.In addition,with the increase of equivalent ratio,the time required for the flame to pass from the open end to the closed end becomes shorter,the time of the peak flame front velocity and overpressure peak appears earlier,and the maximum flame front velocity and overpressure also become larger.When the equivalent ratio is 1.2,the maximum flame front velocity and maximum overpressure appear,which are 50.82 m/s and 34.97 kPa,respectively.With the increase of the CH4 volume fraction,the time required for the flame to pass from the open end to the closed end becomes longer,and the longest flame propagation time(285 ms)occurs when the CH4 volume fraction is 70％.The peak of flame front velocity and overpressure appears later,and the maximum flame front velocity decreases.But the maximum overpressure shows a trend of increasing.When the CH4 volume fraction is 70％,the maximum overpressure peak value is 50.21 kPa.
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