針對受聲波激擾之雙圓盤同心旋轉噴流火焰，使用實驗方法研究噴流火焰出口的火焰特性。中心噴流與旋轉環噴流的流體分別為丙烷與空氣，利用揚聲器產生聲波中心噴流的波擾。利用一維熱線風速儀量測中心噴流的出口速度訊號;籍由擷取瞬時火焰照片辨識督焰特徵模態，擷取長時間曝光的火焰照片，量測火焰的特徵 長度;使用自製的L型細線熱電偶量測火焰溫度;空用氣體分析儀偵測火焰燃燒生成物的濃度。在激擾史卓數、噴流振盪強度及旋轉噴流流雷諾數的域面上，可畫分出四個火焰特徵模態: 藍色根部皺紋火焰、黃色根錨狀火焰、藍色根部錨狀火焰及跳離火焰模態。跳離火焰的火焰顏色是藍色，火焰高度短，具有高紊流，不易熄滅。當燃燒火焰被激擾在藍色根部錨狀火焰及跳離火焰模態時，火焰長度明顯的縮短，火焰溫度激烈地增加，未燃碳氫化合物、一氧化碳、氧化氮的偵測含量極少。跳離火焰在大振盪強度時形成，由於激烈的紊流混合效應，呈現預混火焰的特性，相較於其他火焰模態，藍色火焰長度短且穩定，燃燒效率佳，產生較少有害的燃燒生成物。聲波激擾有效地提升雙圓盤同心旋轉噴流火焰的燒燒性能。

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 “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). At large central fuel jet Reynolds numbers, the unexcited rich-combustion flames exhibited a long and soot-radiating yellow flame which had low combustion performance. By applying appropriate acoustic excitation, the rich-combustion flames presenting 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 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. On the other hand the acoustic excitation can significantly improve combustion performance of dual-disk double-concentric jet flames at medium swirling strengths (275 < Rea < 1300). Four characteristic flame modes, blue-base wrinkled flame, yellow-base anchored flame, blue-base anchored flame, and lifted flame, were observed in the domain of excitation Strouhal number, central jet pulsation intensity and annular swirling jet Reynolds number. 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 lifted flame, which was formed at large central jet pulsation intensities, presented characteristics of a premixed flame due to significant mixing induced by violent, turbulent flow motions. It was short and stable, with high combustion efficiency and low toxic emissions, when compared with the unexcited flame and other excited characteristic flame modes, which presented characteristics of diffusion flame. The acoustic excitation should not be applied to swirling dual-disk double-concentric jet flames at Rea < 275 and Rea > 1300 because the excitation, even at very low pulsation intensities, could easily cause the flame to blow out.

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