Acoustic enhancement of combustion in lifted nonpremixed jet flames

作者：Demare D; Baillot F^*

来源：Combustion and Flame, 2004, 139(4): 312-328.

DOI：10.1016/j.combustflame.2004.09.004

• lifted nonpremixed jet flame
• turbulent combustion
• acoustics
• pulsed combustion
• hydrodynamic instabilities

Lifted nonpremixed jet flames are often used in industrial processes and present inherent difficulties such as their reattachment to the burner, blowout, and poor combustion. One solution is to control the jet by acoustic forcing. For flames lifted in the hysteresis zone where anchoring may occur, forcing at high amplitudes and middle frequencies (around 200 Hz) changes the combustion regime and prevents reattachement. The common long yellow plume, due to soot radiation, vanishes. The flame becomes shorter, totally blue and stabilizes at a higher position above the burner. The phenomenon is explained using the results obtained by analyzing the flow dynamics with highspeed laser tomography, laser Doppler anemometry, particle image velocimetry, and Mie scattering techniques. Measurements show that the excitation periodically generates axial velocities higher than the maximum velocity of the hysteresis zone, leading to flame liftoff. Some primary and streamwise eddy vortices similar to natural instabilities develop during the jet deceleration. Contrary to the unexcited case, these structures, disorganized by the superimposition of the forcing wave, lead to quasi-homogeneous turbulence which provides efficient mixing and improves the combustion regime. Finally, the frequency is sufficiently high to avoid excessive fluctuations of the lift-off height and the reattachment to the burner.

• 出版日期2004-12