Research On The Coupling Mechanism Of Thermal Radiation And Reaction During Flame Propagation

Combustion is the driving force of social development and scientific and technology.The in-depth understanding of combustion process and characteristics is the theoretical basis of clean and efficient utilization of energy.In high temperature combustion system,thermal radiation has significant influence on the energy transfer and temperature distribution during flame propagation.In order to accurately simulate combustion characteristics,the radiative heat loss of downstream combustion products and the radiation reabsorption effect of upstream fuel gases should be considered sufficiently.In this study,the PREMIX code was used to numerically simulate the one-dimensional steady-state laminar premixed flame,and the thermal radiation during flame propagation was calculated in combination with different radiation models.The influence of thermal radiation on combustion characteristics in a variety of fuel systems and combustion conditions was quantified.Through rate-of-production analysis and sensitivity analysis,the coupling mechanism of thermal radiation and reaction was revealed.Firstly,the combustion process of two hydrocarbon fuels(methane and aviation kerosene)under different pressure and equivalence ratios was simulated by using different radiation models.The effects of thermal radiation on flame speed and NO emission were quantified by the relative differences in combustion characteristics between the radiation model and adiabatic model.The calculation results showed that,due to the energy loss outside,radiative heat loss led to a slight decrease in the laminar flame speed of hydrocarbon fuels.However,considering the radiation reabsorption,due to the redistribution of radiative heat inside the flame,the radiative heat loss in the high temperature zone downstream was no longer overestimated,and the unburned fuels in the low temperature zone upstream were preheated,so the flame temperature in the reaction zone was higher than that in the adiabatic condition,and the flame speed increased significantly.Under different equivalence ratios,the flame speeds of methane and aviation kerosene increased by 7.45%and 12.16%,respectively.Further study showed that in addition to the direct radiation effect,the chemical effect induced by radiation preheating was the key factor affecting the combustion characteristics.The results of rate-of-production analysis and sensitivity analysis showed that the key elementary reactions closely related to the flame speed were affected by radiation preheating,and the change degree of reaction rate under different working conditions was the main reason for the different performances of thermal radiation.Subsequently,the above analysis system was further verified and expanded in two different types of zero-carbon fuels,biomass pyrolysis gas and ammonia-hydrogen fuel.The results showed that radiation reabsorption had similar effects on the flame speed and active radical concentrations of ammonia-hydrogen flame and biomass pyrolysis gas as hydrocarbon fuels.In the biomass pyrolysis gas flame,which considered the fuel-NO,NO emission was also controlled by radiation thermal effect and preheat-induced chemical effect.While due to the stronger radiation characteristics of ammonia,the radiation reabsorption effect had a more obvious influence on its flame speed,which can be up to 15.17%in the fuel-rich condition,higher than hydrocarbon fuels.This study showed that radiation reabsorption significantly improved the prediction accuracy of flame combustion characteristics,which should be included in the quantitative calculation of combustion characteristics in the future.Further research on the coupling mechanism of thermal radiation and reaction during flame propagation is expected to play an important role in improving the previous chemical kinetics model,guiding the improvement of combustion characteristics and regulating pollutant emission.