Study On Premixed Flame Dynamics Of CH₄/O₂/CO₂ Mixtures

With the rapid development of the world economy,the total demand for fossil energy such as coal and natural gas is increasing.However,accidents still occur during coal mining and natural gas use,it is particularly important to ensure life safety during energy production and use.Therefore,it is necessary to analyze the flame propagation dynamics,which will help find safety problems in the process of energy production and use,it also indirectly provide a scientific basis for accident prevention.This paper takes the CH4/O2/CO2 premixed system as the research object.The explosion experiment is performed in an elongated duct.The purpose of the experiment was to study the propagation dynamics of premixed flame.The experiment designed five equivalence ratios,i.e,?=0.6,0.8,1.0,1.2,and 1.4,the oxygen fraction γ in oxidant increased from 0.20 to 0.60 with the increment Δγ of0.05.The flame pattern and structure,flame front dynamics and explosion overpressure dynamics were analyzed under the different constrained conditions in the experimental duct.The study found that the buoyancy flame,tulip flame and finger flame dominate flame types under all equivalence ratios ?.Increasing the duct length-diameter ratio is beneficial to the development of the whole tulip flame process,and the range of γ of tulip flame will also be widened.The difference of the length-diameter ratio has little effect on the variation trend of flame front propagation velocity V and the evolution trend of explosion overpressure P.However,under a larger length-diameter ratio,the γ for generating the pressure curve with a single peak overpressure is smaller.Compared with the half-open,the flame assumed the buoyancy flame,tulip flame and the distored tulip in the closed duct.In the closed duct,the tulip flame dominated the flame pattern.The stronger compression may be the reason of tulip-typed flame in the closed.In addition,the difference between flame propagation dynamics and explosion overpressure dynamics under different ducts is mainly reflected by the non-standard oscillation phenomenon of flame front propagation velocity V curve and the fluctuation phenomenon of explosion overpressure P curve.Changing the duct configuration(the open/closed duct),the flame structure was still dominated jointly by the combination of ? and γ dominant.The coupling analysis on the flame structure,the flame velocity V and the pressure P shows that flame structure dominates the flame velocity,and the duct configuration have little influence.There is a good linear relationship between the laminar burning velocity(LBV)and the oxygen fraction γ.There is a similar linear relationship between the LBV and Vmax and Pmax,respectively.The linear relationship will not be affected by the duct configuration.Therefore,as a single index,LBV showed the superior potential in predicting the explosion pressure.The stronger compression would be the primary factor affecting the prediction of Pmax by using LBV for the closed duct.