Abstract
Abstract: The acoustic excitation effect on flame characteristics of a diffusion flame jet inside a cylindrical tube has been presented and discussed. The flame under acoustic excitation has complex geometrical patterns, colours and dynamics. Three acoustic zones have been examined in detail. In the rarefaction zone, it has been observed that the yellowish diffusion jet flames change colours to blue either partly or completely, which imply the significant change in chemical reaction and the importance of burner nozzle position relative to the combustion chamber. In the high velocity fluctuation zone, mushroom like flame shape and flame necking are present and it seems that the high velocity fluctuation only affect the bulk movement of the flame. In the compression zone, no obvious flame change could be observed directly. Multiple signal measurement and analysis of jet flame dynamics in a loudspeaker induced standing wave have been presented. The sound pressure, velocity and the simultaneous measurement of two chemical species are carried out. The acoustic and velocity signals were measured at cold conditions along the central axis of the cylindrical tube in which the standing wave was created. Without acoustic excitation, the CH* and OH* signals are slightly out of phase. The flame oscillates around 13 Hz and sub harmonics are clearly visible. With acoustic excitation, the spectra have more chaotic frequency peaks. The space phase diagrams are less in phase in comparison with those without acoustic excitation.