Improving combustion performance of swirling double-concentric jets flames with rich equivalence ratios

Abstract

The acoustic excitation method was used to improve the combustion performance of rich-combustion flames of swirling dual-disk double-concentric jets. The unexcited and excited conditions were compared. The central jet was propane gas and the swirling annular jet was air. The central fuel jet was acoustically excited by a loudspeaker that was installed by the “downstream longitudinal irradiation” method. A home-made, one-component hot-wire anemometer was used to measure the central jet velocities to reveal the jet pulsation behavior. Long and short exposure flame images were captured for identification of flame behavior. A home-made L-shaped fine-wire thermocouple was used to measure the flame temperatures. A gas analyzer was used to measure the concentrations of main combustion products, including carbon dioxide (CO2), unburned hydrocarbons (UHCs), carbon monoxide (CO) and nitric oxide (NO). The process parameters (Rec, Rea, Stexc, and Ip, identified in the nomenclature) able to provide higher combustion efficiency were introduced. The best operating zones of the unexcited and excited flames were observed. At large central fuel jet Reynolds numbers, the unexcited rich-combustion flames exhibited a long and soot-radiating yellow flame that had low combustion performance. By applying appropriate acoustic excitation, the rich-combustion flames presenting a soot-radiating yellow appearance could be changed to short, blue, high-turbulence, high-stability lifted flames and the combustion performance was improved. The acoustically excited lifted flame had a higher temperature and lower toxic emissions when compared with the unexcited flame. According to the presented results, two strategies of operating the burners of swirling dual-disk double-concentric jets at low and high central fuel jet Reynolds numbers were suggested.