Experimental Study On Rapid Phase Transition Induced By Methane Combustion Under Oxygen-rich Conditions

As the main energy source in China at present,coal resources are supporting the development of the country and society,while its reserves are decreasing,and coal burning has caused problems such as global warming and environmental degradation.Therefore,the search for clean energy and efficient combustion technology has become an important issue for human beings,and natural gas and oxyfuel combustion technologies have attracted attention.However,the combustion of natural gas under oxygen-rich conditions is highly prone to combustion-induced rapid phase transition and cause explosion accidents,causing huge losses to the country and the people.Based on this,the effects of oxygen enrichment coefficient and venting area ratio on explosion characteristics are analyzed by constructing a closed vessel combustion-induced rapid phase transition experimental bench,a long pipeline combustion-induced rapid phase transition experimental bench and a transparent pipeline combustion-induced rapid phase transition experimental bench,and the pressure oscillation characteristics and flame oscillation characteristics were analyzed comprehensively.The formation conditions and essential characteristics of methane combustion induced rapid phase transition under oxygen-rich conditions are clarified.The research results provide theoretical basis and technical reserve for the design and safe operation of oxy-combustion equipment.The main research contents and conclusions are as follows:(1)The experimental bench of combustion-induced rapid phase transition of a closed vessel was designed and constructed.The oxygen air enrichment factor E was changed to 0.21(air),0.4,0.6 and 0.8,respectively.Combined with the adiabatic pressure and temperature calculated by Gaseq program,the effect of oxygen enrichment coefficient on combustion-induced rapid phase transition was investigated.The results show that the peak value of explosion pressure increases with the increase of oxygen enrichment coefficient.This is because as the oxygen-rich coefficient increases,the nitrogen content in the premixed gas gradually decreases,the flame temperature and blackness gradually increase,and the flame radiation intensity and radiation heat transfer gradually increase,eventually causing the peak value of the explosion pressure to continuously increase.When E=0.21,the explosion pressure has no oscillation phenomenon;when E=0.4,0.6 and 0.8,the pressure peak is higher than the corresponding adiabatic pressure,and the explosion pressure causes an oscillation phenomenon.(2)The long pipeline combustion-induced rapid phase transition experimental bench was used to study the pressure characteristics of the combustion-induced rapid phase transition phenomenon in the closed and blasting conditions.The effects of oxygen enrichment factor E and venting area ratio S on explosion pressure and peak time of explosion pressure were analyzed.The results show that when E=0.3,there is a pressure oscillation phenomenon that does not reach the peak of superadiabatic pressure.This is because the adiabatic temperature at this time is higher than 2600 K,but it is much lower than 3100 K,although the liquid film undergoes a phase change,but there is no explosive evaporation boiling,so although the explosion pressure oscillates,there is no peak of the super adiabatic pressure.Under the deflation condition,the pressure peak gradually decreases with the increase of the venting area.This is because as the ratio of the venting area increases,the area of the end wall surface gradually decreases,the degree of gas turbulence caused by the reflection is weakened,and the explosion pressure gradually decreases.It was also found that the pressure peak at S = 0.25,0.5,0.75 and 1 was much lower than the pressure peak at S = 0.(3)The self-designed transparent pipeline combustion induced rapid phase transition test bench was used to study the flame oscillation characteristics and pressure oscillation characteristics by changing the oxygen enrichment coefficient E and the venting area ratio S,and carried out a comprehensive analysis.The results show that when E=0.21,the flame of the tulip appears,and the flame has no oscillation.When E=0.3,0.4,there is no tulip flame,the flame appears to oscillate,and the oscillation phenomenon in the late stage of the flame becomes more and more obvious with the increase of the oxygen-rich coefficient.It was also found that when E=0.21,the explosion pressure had no oscillation and gradually decreased with the increase of the venting area ratio;when E=0.3,0.4,the pressure oscillation period was within the same order of magnitude,and with the venting area ratio S increased,the amplitude of the pressure oscillation gradually increased.