On the Role of Large and Small-Scale Structures in Combustion Control

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Abstract
Experiments were performed to actively control combustion between coaxial air and fuel jets. The objective was to initiate the combustion as close as possible to the flameholder surface and to maintain uniform combustion in the entire mixing region. Forcing was applied to both the air and fuel streams. at different frequencies and amplitudes. The air jet was excited at its preferred mode frequency while the fuel was forced at higher harmonics in order to trigger and amplify the initial instabilities of the coaxial jet. Nonreacting tests showed that the combined forcing was promoting an earlier transition to small-scale turbulence at the nozzle's exit. Consequently. the combustion was enhanced and became uniformly distributed along the flame. contrary to the reference unforced flame where intense combustion started only at a distance from the flameholder and was limited to the region where vortical structures developed. The optimal combination of forcing parameters are presented and discussed.

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