Effect of acoustic excitation on flames of swirling dual-disk double-concentric jets

The flame behavior of acoustically excited combusting swirling double-concentric jets with a dual-disk flow controller at the jet exit was experimentally studied. The fluids for the central and swirling jets were propane and air, respectively. The central jet was acoustically excited using a loudspeaker. The central jet velocities were measured with a one-component hot-wire anemometer to estimate the acoustic excitation behavior. Close-up and full-length short-exposure and time-averaged flame images were captured using traditional photography techniques. The flame temperatures were measured using a homemade L-shaped fine-wire thermocouple. The combustion product concentrations were measured using a gas analyzer. Three characteristic flame modes-yellow-base anchored flame, blue-base anchored flame, and lifted flame-were observed in the domain of the excitation Strouhal numbers and jet pulsation intensities. The lifted flame was blue, very short, highly turbulent, even at low Reynolds numbers, and difficult to blow out. The flame length was significantly reduced, and the flame temperatures were drastically increased when the combusting jets were forced into the characteristic modes of blue-base-anchored and lifted flames. The concentrations of unburned hydrocarbon, carbon monoxide, and nitric oxide fell to negligibly small values. The acoustic excitation was effective in promoting the combustion performance of the swirling double-concentric jet flames.