Numerical And Experimental Study Of The Heat Release Rate Quantitative Measurement Using Chemiluminescence In Premixed Methane-air Flames

Because of the very complicated combustion flow in the scramjet,it is very necessary to use advanced combustion diagnostic technology investigate it.The combustion diagnostic based on the chemiluminescence can obtain effective combustion information,and the signal collection of chemiluminescence is very convenient.On this basis,the computed tomography of chemiluminescence technique is especially suitable for the study of 3D unsteady combustion flow fields and flame structure which has great value for research.Numerical and experimental studies on laminar methane-air premixed flames were performed to investigate the characteristic of combustion and chemiluminescence,also analyzed the flame structure.At the same time,the quantitative correlation between the combustion information especially the heat release rate(HRR)and chemiluminescence was determined in this paper.The CHEMKIN-pro package and a detailed reaction mechanism,namely,GRI-Mech3.0,incorporating sub-reaction models for excited state radicals(OH~*and CH~*)over a flat flame were employed in this study.The present work investigated heat release of elementary reactions and the reaction path of excited state radicals,given the reason of chemiluminescence marks heat release rate.Through contrasting the distribution of excited state radical concentration and heat release rate,this paper came up with an evaluation index for determining the best heat release rate marker.Based on the result of numerical simulation,experimental study on flat flame was carried out.The present work measured the distribution of temperature and heat release rate using a coated Pt/13%-Rh-Pt thermocouple,and the distribution of chemiluminescence was measured by ICCD camera.The effect of equivalence ratio and flow velocity on the flame structure and characteristic of chemiluminescence were analyzed.It was shown that with the increase of flow velocity the peak value of heat release rate and chemiluminescent intensity shown increases but the location of peak value remain relatively unchanged;With an increase of equivalence ratio,the peak value and gradient of temperature are increasing,the peak value against the flame height above the burner is decreasing,the velocity of reach peak temperature is increasing as well.Both of the OH~*and CH~*chemiluminescence can determine the location of heat release and the OH~*is more effective.The experimental observation shown that chemiluminescent intensity ratio is a monotonic function of equivalence ratio,with the increase of equivalence ratio the intensity ratio shows decrease.The peak of heat release rate as a linear function of the peak chemiluminescent intensity,and with the increase of equivalence ratio,coefficient of proportionality is decreasing.Furthermore,this paper investigated the 2D premixed flame.A reduced reaction mechanism which contain 19 species and 39 reactions was employed to simulate the distribution of temperature and heat release rate,the effect of equivalence ratio and flow velocity on burning velocity was analyzed as well,which in agreement with theory.The comparison of heat release rate and chemiluminescent intensity shown that both of OH~*and CH~*chemiluminescence also can determine the location of heat release,and peak OH~*chemiluminescent intensity as a strong linear correlation of the peak of heat release rate,which has no connection with equivalence ratio.In contrast,the relation of CH~*chemiluminescent intensity and heat release rate is undefined.On the other hand,the correlation between chemiluminescent intensity ratio and equivalence ratio acquired in flat flame also apply to 2D flame.It is acceptable that we can measure heat release rate and equivalence ratio quantitatively using the chemiluminescence.