(An) experimental study on the combustion characteristics in a helmholtz type pulsating combustor

Abstract

In spite of the merits of high transfer, low pollutant emission and compact combustion, direct and/or indirect application of pulsating combustion system is at a low ebb due to the strong noise and the lack of physical understanding. Knowledge on the physical natures of the heat addition process coupled with the acoustic wave, unsteady flame structure and the effect of heat input or bumer geometry on the change in the operating characteristics would be a key factor in determining a way for the effective control of the pulsating combustor. The purpose of this study is physical understanding of the periodic combustion processes in the Helmholtz-type pulsating combustor. To realize it, pulsating combustion processes were observed form the following three standpoints: (1) operating mechanism, (2) mixing conditions for the achievement of stable pulsation and indirect control of the burner and (3) spatially distributed heat release rate for the explanation of stability. Through the image processing of the direct visualization and the relationships between the fuel consumption rate and operating frequency or the moving velocity of the periodic flame, pulsating flame``s behavior and the operating response will be explained. Four tried nozzles and the effects of the stabilizer on the frequency and pollutant emission are investigated for the mixing rate and the stabilization of the flame front and to suggest the way of the pulsating combustor control. Finally, the space and heat release rate suggested from the results of ion current measurements is introduced for the local stability test represented as a Rayleigh criterion. The following conclusions can be made from this experimental study. Volumetric expansion of the flame attached at the edge of the stabilizer occurs in the main reaction period which corresponds to the pressure increasing. Ignition occurs by mixing fresh reactants with a hot residual flame which has a shape of a sooty luminous flame. This continuous re...