| The utilization of gas and natural gas constitutes the framework of China’s energy structure.Due to its large scale,it has important research value in energy efficient utilization,energy conservation and emission reduction,and safety.Among them,oxygen-rich combustion,as one of the feasible technologies that can improve the utilization efficiency and achieve zero emissions,has attracted extensive attention.Gas contains a certain concentration of methane,while the main component of natural gas is methane,so it is of great significance to study the combustion characteristics of methane under different oxygen conditions.Under oxygen-rich conditions,the methane combustion explosion will produce a combustion induced rapid phase transition,which is a phenomenon accompanied by a sudden rise in the maximum pressure,up to nearly 4×10~4 k Pa.In the industrial process has a great harm,not only because it can produce very high overpressure,and very fast pressure rise rate,may make the equipment of the explosion device failure,and then cause a great harm of the accident.At the same time,the oscillation of pressure and flame will also occur,which will cause greater harm under the synergistic action of pressure and flame oscillation.In this paper,the flame-pressure coupled oscillation law and mechanism of methane/oxygen/nitrogen premixed gas explosion are deeply explored through experiments and numerical simulation,which will also play a positive role in enriching and improving the theory of combustible gas explosion.In this paper,methane/oxygen/nitrogen mixture premixed gas was used to carry out experiments under the conditions of 0,250,500,750 mm IP at different ignition positions and0,0.25,0.50 and 0.75 S at different open area ratios,respectively.The difference of flame structure is mainly reflected in the shape of the flame front.When IP=0,the flame front is"finger-like";when the oxygen enrichment coefficient E increases,the flame speed is significantly accelerated,and the"tulip"flame appears on the flame front.When the ignition position IP=250,500 and 750 mm,it was found that the flame structure had similar structure before the flame front came out of the open end,and after the flame front came out of the open end,the flame and pressure oscillated more obviously with the increase of the ignition position.When the area ratio of different openings increases,the pressure and flame oscillation are significantly enhanced,which indicates that the synergism of pressure and flame coupled oscillation is enhanced when the ignition location IP and the area ratio of openings S are increased.The coupling oscillation of pressure and flame is theoretically analyzed.Under different reaction conditions(different ignition positions and different open area ratios),the unburned gas will transmit the pressure fluctuation generated by the reaction to the burned gas through the flame surface,so that the flame length will change.The water in the product may be partially cooled into liquid water,and the pressure at the pipe wall decreases.Under the action of high temperature flame radiation,some liquid water is converted into water vapor.The pressure at the pipe wall increases,and the pressure difference affects the flow field.In order to analyze the coupling oscillation pressure and fire law,by increasing laminar flame model and surface model,under different conditions,the methane/oxygen/nitrogen mixture premixed gases are simulated,and through the experimental results of the flame structure and pressure change trend has carried on the contrast,prove that the model experiments can be better.By changing the ignition position,the oxygen enrichment coefficient E=0.21 was numerically simulated,and the simulation results showed that the flame structure was similar in different conditions before the flame surface efflux pipe,and the flame structure changed in different conditions after the flame surface efflux pipe.The velocity vector diagram and reaction rate diagram of different working conditions were observed,and the changes of flow field were analyzed. |
