Abstract
This paper presents the results of experimental studies that have been performed on the confinement air jet flow at the exit of the burner, and further upstream inside the Rijke tube with and without excitation were quantified by CTA Anemometer. To understand more about three regimes (compression, high velocity fluctuating, and rarefaction (Farhat et al., 2005)) a full mapping of the velocity field has been obtained for all non-reacting flow. The third mode of the Rijke tube has been selected for detail investigations, since this is the lowest mode which has three regimes. A very important observation of the velocity close to the fuel nozzle is much higher than expected when under acoustic excitation. Comparisons and investigations of the velocity characteristics with and without excitation at different positions above the nozzle exit have been carried out. The results show that the axial local velocity was observed to increase by three times at the rarefaction regime, compared with the other regimes the local mean velocity is approximately remain the same as for flow without excitation. It seems to be that the surrounding air is mixed with the air jet exiting from the nozzle resulting in an accelerated jet of air. At similar condition of excitation, and with the air jet replaced by a propane fuel flame, the laminar propane diffusion flame becomes completely blue in colour, shorter in height, and also lifts off in the rarefaction regime, and a mushroom like flames and flame necking are observed in the high velocity fluctuating regime (Farhat et al., 2005). This indicates that the acoustic excitation may have enhanced the mixing of the air and fuel in a rarefaction regime.