Concentration measurements of selected hydrocarbons in methane/air partially premixed flames using gas chromatography

Concentrations of selected hydrocarbons (viz. CH4, C2H6, C2H4 and C2H2) have been measured in CH4/air partially premixed flames for different primary mixture equivalence ratio (ϕ) and primary jet velocity using gas chromatography. Visual observations of the flames are also made using digital photography. An axi-symmetric, co-flowing burner is placed on a traversing stage and a quartz probe is used for the collection of the gas sample by placing it at appropriate locations with respect to the burner. The double flame structure is observed with the increase in the premixing air with the fuel. At a high premixing air, the inner flame turns from blue to a greenish one. Hydrocarbons are detected only inside the inner flame structure of the partially premixed flames at all equivalence ratios studied and the concentrations of the non-fuel hydrocarbons are much less than in the non-premixed flames at most of the locations. The peak C2H6 and C2H4 concentrations are found to be the maximum in a partially premixed flame with an intermediate ϕ, while peak C2H2 concentration continually decreases with the decrease in ϕ. The partial premixing decreases the radial transport of species at lower elevations mainly because of the high axial velocity of the primary jet. At higher elevations within the inner flame the radial distribution of C2H4 and C2H2 concentrations show the peak value to exist at the centerline.