Investigation Of Stability And Chemiluminescence Characteristics In Lifted Inverse Diffusion Flame

Gaseous hydrocarbons include natural gas,coke oven gas,shale gas,etc.At present,the preparation technology of syngas which uses gaseous hydrocarbons as a raw material has been developed maturely around the world.There are many kinds of products made from syngas with high economic benefits.At present,the industrialization of related products is quite mature.Inverse diffusion flame is an important form of jet diffusion flame,which is widely used in industrial fields such as non-catalytic partial oxidation of methane.Flame spectrum diagnosis can determine the flame position,equivalent ratio,etc.and can also explore the characteristics of the flame itself such as the flame stability.The method of spectral diagnosis can reflect the process of flame redox reaction more comprehensively,so as to better monitor the flame and provide a basis for the stable operation of industrial devices.In this study,the stability and chemiluminescence characteristics in CH4/O2 lift-off inverse diffusion flame were investigated.The OH*and CH*radiation characteristics,lift-off height,and transition(attachment,lift-off and blow-out)of flames under different conditions were discussed.A two-dimensional model was established to simulate the different conditions of inverse diffusion flame using ANSYS software,and the formation path and reaction mechanism of OH*radicals in different positions of the flame were analyzed in detail,which laied a theoretical foundation for flame diagnosis.The results indicated as follows:(1)In the methane/oxygen liftoff inverse diffusion flame,the reaction is the most intense at 3mm above the flame root.With the increase of oxygen velocity,the peak intensity of OH*radical radiation,the flame height and the radial size of OH*decrease,and the reaction zone of the flame moves down gradually,while the main reaction zone moves closer to the central axis.The trend of radial dimension in CH*is similar to the OH*.As the gas velocity increases,the radial dimension of CH*decreases.Compared to the OH*distribution,the CH*generation area is smaller and the radial dimension is less than that of OH*.With the methane velocity increasing,the oxygen velocity that forms the liftoff flame decreases,and the blowout limit increases.After the methane velocity reaches a critical value,increasing the oxygen can not form a liftoff flame,and the flame blows out directly.At the flame root and OH*peak position,the main generation path of OH*are H+O+M=OH*+M and CH+O2=OH*+CO,and the main quenching path of OH*is OH*=OH+M.Because lots of intermediate substances(CO,CH,etc.)are generated during the flame chemical reaction,OH collides with the intermediate substance ions to generate OH*.(2)The nozzle structure affects the stability of the inverse diffusion flame.When the thickness of the nozzle rim is less than 0.5mm,with the oxygen velocity increasing,the flame will change the state as attachment-liftoff-blowout When the thickness of the nozzle rim is more than 0.5mm,the flame will directly change from the attachment state to the blowout with the increase of oxygen velocity.Besides,the values of the blowout limit of the nozzle is inversely proportional to the rim thickness of the flame.The thicker the rim of the nozzle is,the smaller the air velocity of the blowout limit is,and the easier to blow out.The thickness of the nozzle rim will affect the size of the backflow area at the flame root and the shape of the flame.As a result,with the increase of the thickness of the nozzle rim,the radial size of the flame and liftoff height decreases.Different incident angles will result in various shear angles,which will affect the flame structure.The thrust gas velocities of nozzles with an incident angle of 75°,60° and 45°are close to that of nozzles with an incident angle of 90°.The nozzles with an incident angle of 45° generally have higher flame liftoff height than those of the 90°,75° and 60° nozzles,and the OH*radial dimension is generally larger than other nozzles.The peak of OH*radical radiation in flame with an incident angle of 75° is higher than other incident angles,and the peak of OH*radical radiation in flame with an incident angle of 45° is the lowest As the incidence angle decreases,the tangential velocity of flame increases and the flame tends to be more stable.