The acoustic response of burner-stabilized premixed flat flames

The behavior of acoustically driven flat flames has been analyzedexperimentally. In this study pressure transducers and Laser DopplerVelocimetry are used to characterize the acoustical waves upstream anddownstream of a flat flame stabilized on a flame holder. Two different flameholders have been used, i.e. a perforated brass plate and a ceramic foam,exhibiting very different surface temperatures. From these experiments theacoustical transfer function can be derived. This transfer function shows aresonance-like behavior, of which the shape and peak frequency is governedmainly by the surface temperature of the burner and the velocity of the unburntmixture. The brass burner exhibits a resonance frequency around 140~Hz, wherethe resonance of the ceramic burner seems to have moved to much higherfrequencies and is much more damped. All results can be understood very wellwith an analytical model in terms of Zeldovich number, stand-off distance andheat conductivity. Apart from the analytical model, for the brass flame holderalso numerical simulations with detailed chemistry have been performed. Again,the correspondence is good. The most interesting application is the acousticbehavior of central heating systems, in which these burners are frequentlyused. For the purpose of modeling the acoustical behavior of complete boilersystems, the analytical model can be used with minor adjustments to theZeldovich number and heat conductivity, yielding a fairly accuratesemi-empirical model describing the transfer function.