Control of Flame Oscillations with Equivalence Ratio Modulation

Abstract

A novel technique for controlling oscillating combustion is proposed and demonstrated. For oscillations that exist over a limited range of equivalence ratios, we suggest that periodic modulation around the unstable condition can effectively avoid the oscillating condition, but otherwise produces the desired timeaverage equivalence ratio. Tests of this concept were carried out in an atmospheric-pressure, swirl-stabilized combustor with a nominal heat input of 30 kW. The fuel was natural gas. We show that it was possible to control a 300-Hz oscillation by modulating the fuel flow at frequencies less than 20 Hz, reducing the observed rms pressure from 2.7 to 0.8 kPa. Limitations on when this technique may produce successful control are also discussed.