Electric Field Damping of Rijke Tube Combustion Instabilities

摘要

A direct-current electric field was investigated as a damping method for thermoacoustic instabilities generated in a horizontal Rijke tube driven by a premixed propane torch. Electrode lengths of 2.54, 5.08, and 15.24 cm were used with electrode locations relative to the burner tip of -4.60, -2.06, and 0.458 cm and voltages up to 4.68 kV being tested. Electrodes downstream of the burner tip, rather than surrounding the burner, and longer electrodes were most effective at damping instabilities. Damping also increased with applied voltage. These findings held true for both laminar and turbulent flames and were in agreement with theoretical predictions made based on two-dimensional static electric field models. Sound pressure level reductions up to 21 dB for the laminar flame, which completely damped the instability, and 4.4 dB for the turbulent flame were seen using the 15.24 cm electrode at 4.68 kV. When the entire Rijke tube acted as the electrode, a reduction of 19 dB was seen for the turbulent flame at 9 kV, which suppressed the instability. The damping effect was attributed to stabilization of the oscillating flame and its unsteady heat release, driven by the combustion instability pressure fluctuations, via the ionic wind.