Acoustic Instability
Background & Objective
In the various industrial combustion system, the combustion instability is of significant importance. Particularly, the interactions between combustion and acoustic instability are more significant issue since it could lead to serious damage or shortened lifetime on combustor. A phenomenon of interactions between combustion and acoustic instability play a role in industrial applications such as gas turbines, rocket engines, etc., Research on such thermo-acoustic instability has been conducted for a long time in various ways; experiments of a flame propagating in a tube have been most frequently adopted among other manner. Therefore, we have been conducting research of a flame propagating in a tube. One of the purposes is to study about mechanism of interaction between flame and pressure fluctuation. And also, investigation about effect of dominant parameters for acoustic instability.
Fig. 1 Schematic drawing of experimental apparatus
Research
We utilize a novel method, the CO2 laser irradiation method, to control the shape of freely propagating flames. The external laser irradiation preheats an unburned mixture locally in front of a reaction zone, and the flame propagation velocity increases locally, and here the flame front acquires a strongly curved shape. With this, we have conducted experiments on downward propagating flat flames (Fig.2) with CO2 laser light and have observed unique deformation of the flame surface (Fig.3, called as ice-cream flame) from a flat flame surface caused by primary acoustic instability when flame front is exposed to CO2 laser light. Since then, we have examined the extent of a transition from the primary to the secondary acoustic instability (Fig.4) using a short-term CO2 laser irradiation method. At now, we also have been conducting upward propagating flame.
Fig. 2 Sequential images for propagating flame
Fig. 3 distinctive flame behaviors of transition with laser irradiation
Fig. 4 The feature of behavior on upward propagating flames