| With the rapid development of world industrial economy,environmental ecology and industrial safety are becoming more and more important.For the production,transportation and utilization of methane and other combustible gas industries,combustible gas explosion is a serious threat to human safety and causes huge equipment and property losses every year.At present,the research on combustible gas explosion mainly focuses on deflagration and detonation.Deflagration is the main mode of methane in industrial production,but the evolution and intensity of methane deflagration are affected by a variety of factors,such as gas component concentration,confined space size,detonation discharge conditions,obstacles,ambient temperature and humidity.Therefore,it is of great theoretical value and engineering significance to study the characteristics of methane deflagration flame and overpressure under complex conditions.In this paper,through the research method combining experiment and numerical simulation,the propagation characteristics of CH4/O2/N2 premix deflagration under complex conditions are explored from the perspectives of deflagration space,oxygen enrichment coefficient,ignition location,wall temperature,water vapor concentration,etc.,which will further enrich and improve the relevant theory,knowledge system and relevant application results of combustible gas deflagration.Firstly,the dynamic propagation characteristics of flame structure,flame front position and flame overpressure in CH4/O2/N2 premix deflagration process were experimentally studied by setting up an experimental platform in the slit space for combustible gas deflagration.It was confirmed that the slit space had a great promotion effect on flame oscillation;The deflagration characteristics of CH4/O2/N2 premix gas at different oxygen enrichment coefficients（E=0.21,E=0.3 and E=0.4）and ignition positions(IP0,IP475 and IP900)were further investigated.The experimental results show that in the slit space,when the ignition position is 475mm(IP475),the flame spreads from the middle of the pipe to both sides,and the flame front and overpressure oscillate most violently.When the ignition position is on the end face（IP0）,the formation time of reflected wave is longer and the peak value of deflagrate overpressure increases.When the oxygen enrichment coefficient increases,the content of oxygen atoms in the premixed gas increases,which further promotes the devolution combustion reaction process,resulting in higher flame propagation speed and devolution overpressure.Secondly,by building a closed experimental platform in a humid and hot environment,CH4/O2/N2 premixed gas at different vapor concentrations of 0 mg/m3,6 x105mg/m3,1.8 x106 mg/m3,3.6 x106 mg/m3,1.08 x107 mg/m3 and different wall temperatures of300 K,323 K,373 K and 423 K conditions about deflagration characteristics of premixed gas.The experimental results show that the peak value of deflagrate overpressure increases first and then decreases with the increase of water vapor concentration.Therefore,it can be seen that low concentration of water vapor can promote the deflagration of premixed gas,while high concentration of water vapor can inhibit the deflagration of premixed gas.When the wall temperature increases from 300 K,323 K,373 K and 423 K,the evaporation and condensation process of water on the pipe wall is inhibited,and the peak value of deflagration pressure decreases.When the wall temperature is less than or equal to the boiling point temperature of water,the evaporation and condensation process of water on the pipe wall is inhibited,and the pressure peak decreases slowly with the increase of the wall temperature.When the wall temperature is higher than the boiling point temperature of water,the deflagration overpressure decreases greatly.Finally,in order to reveal the coupling oscillation law of deflagration pressure and flame,the large eddy model was used to conduct numerical simulation for 9.5%CH4 premixed gas at different wall temperatures（300 K,373 K and 423 K）in hot and humid pipeline.Model built using the same physical model test pipe size,under different mesh size through the analysis of the deflagration flame front position grid independence verification,and under the condition of the optimal grid size,the comparison of pressure change trend of the experimental and simulation results,proved that the model has good inosculation of experimental data.The simulation results further show that the dynamic evolution processes of spherical or semi-spherical flame,finger flame,flame contact wall and tulip flame all occur at different wall temperatures.By observing the pressure change,velocity vector diagram,flame position and flame structure change diagram under different wall temperature,the movement law of deflagration flow field is analyzed,and the direct coupling oscillation mechanism between velocity,pressure and flame is revealed.The conclusion of this study can provide theoretical reference and technical support for enriching and improving the theoretical knowledge of methane deflagration. |
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