Experimental Study Of Low Concentration Methane In An Airtight Pipeline Ignition And Flame Propagation Characteristics

Low concentration methane is widely present in coal bed methane, coal mineventilation air and industrial emission, it is a research hotspot to utilize lowconcentration methane safely and efficiently. Meanwhile, there are many safety issuesin the process of mining, and hazards also exist in gas pipeline. The researching of lowconcentration methane ignition and flame propagation characteristics is helpful tocontrol the degree of damage, there are highly academic significance and industrialapplications to do this research.In this research, an experiment system with micro-thermocouples, ion currentprobes and high-frequency pressure sensors is designed to study combustible gascombustion. In this paper, the experiment system is utilized to study the properties oflow concentration methane combustion, experiment results reveal the effects of flamepropagation properties which affected by gas initial parameters and tube physicalconditions.The experiment system is utilized to study the properties of methane flamepropagation which affected by gas initial parameters, flame temperature, ion current,flame propagation velocity, flame thickness and pressure are analyzed to reveal theflame propagation. The results show that: the pressure wave velocity is higher than theflame propagation velocity in a closed tube combustion; Due to the disturbance ofpressure waves, flame propagation has an acceleration process, along the flamepropagation, flame propagation velocity, flame thickness and flame peak temperaturehave a certain degree rise; The combustion process is highly affected by initial methaneconcentration, as the increasing of methane concentration, flame propagation velocity,flame thickness, flame peak temperature and peak pressure drop after the first rising,there are maximum values above methane concentration near9.5vol.%. Moreover, asthe increasing of initial pressure, average flame velocity, flame thickness, flame peaktemperature and peak pressure is increased.The experiments under two ignition position show that: the acceleration of theflame propagation is present in the front tube; in the end of tube, due to the impact ofpressure wave reflected by wall, flame propagation have a deceleration process,however, flame peak temperature and flame thickness have a certain increasing; Due tothe effect of pressure relief hole cylindrical space, pressure wave have a deceleration process, but a rising of peak pressure have been detected in experiment.The effects of flame propagation and pressure which affected by three types ofpressure relief hole sealing material are studied, the experiment results show: monolayerfilm could be ruptured by pressure; when the film thickness increased to four, the filmruptured reason is the burning of flame; After replace paper as sealing material, it can’tbeen ruptured during the combustion process. Combustion is obviously impacted bysealing material strength, there is a better flame propagation acceleration effect whenuse higher strength sealing material, it is not conducive to flame propagationacceleration process when sealing material is ruptured, so that the flame propagationvelocity is low in the rear pipe; The peak pressure is obviously affected by sealingmaterial strength, it is not conducive to the pressure gathering when the sealing materialis ruptured, comparing the paper closed style, the n peak pressure which closed by filmis much lower than it.