Experimental Investigation of Some Flame Behaviors Exhibited in Afterburners

Date of Completion

January 2011


Engineering, Aerospace|Engineering, Mechanical




This study concentrates on indentifying, quantitatively tracking, and understanding the dynamics of bluff body stabilized flames as they encounter natural thermoacoustic interactions and as they are no longer able to be stabilized by the bluff body (blowoff). Two combustors are used to study flames held by bluff bodies, a Rijke tube and a large scale combustion rig (the rig). A Rijke tube is used to self excite thermoacoustic interactions in a bluff body stabilized flame. OH-PLIF (planar laser induced fluorescence) and CH* Chemiluminescence measurements are taken with pressure measurements to obtain relations that compare the flame's behavior to pressure (a reasonable variable to measure in afterburners). It is shown that pressure is a good metric of thermoacoustic coupling and that the area perturbation, over several equivalence ratio conditions and bulk flow velocities, all plateaus in a logarithmic fashion as the natural pressure within the combustor rises. POD (proper orthogonal decomposition) was proven to be useful in reducing the line of sight integration errors from chemiluminescence and a spatial Rayleigh criterion is presented. ^ The rig is a large scale combustor that was used to study the blowoff dynamics of flames that had fuel stratification and natural thermoacoustic coupling. For both cases POD was shown to be useful in quantitatively identifying and tracking blowoff dynamics (including vortex shedding and the burning of products in the recirculation zone). This is a novel use of the time constants associated with POD and a more useful way of analyzing image data than qualitatively observing various phenomena or only concentrating on specific areas of an image for quantitative analysis. ^ PIV was used to estimate an average recirculation zone length and this length, along with the higher harmonics from the pressure trace, was shown to help determine whether or not a flame would encounter blowoff prematurely when the flame was naturally thermoacoustically coupled. POD was shown to be effective in observing the higher harmonic acoustic behavior that may be seen from chemiluminescence without POD. ^