||本研究實驗探討燃燒室中控制火焰驅動/抑制燃燒不穩定之主要基構, 特別是探討預混火焰燃燒爐面冷流聲導納對燃燒不穩定之影響。研究中聲導納之獲得乃利用LDV及壓力轉換器直接量取速度及壓力震盪, 以及其震盪之相位關係。研究結果顯示, 火焰驅動/抑制燃燒不穩定之特性主要由冷流聲導納來主導; 不同當量比之火焰顯示相同趨勢, 但不同強度, 並與頻率有關之火焰驅動特性, 這些結果可由所量測之速度及壓力震盪比值以及相位關係來解釋。本研究結果同時顯示, 冷流聲導納之虛部可用來預測火焰驅動/抑制燃燒不穩定之特性。
This research experimentally investigated the mechanisms controlling the flame driving characteristics in combustors. Specifically, effects of the nonreactive acoustic admittance of a laminar premixed flame burner on thermo-acoustic instabilities in an acoustically excited duct were investigated by mainly using acoustic admittance measurements. These admittance data were obtained by directly measuring the amplitudes of pressure (|p'|) and velocity (|v'|) oscillations, and the phase relations between the pressure and velocity oscillations (.psi./sub p'v'/). Results of these studies reveal that the driving/damping characteristics of the investigated flames are mainly dominated by the nonreactive burner admittance. Flames with different equivalence ratios exhibit similar tendency, but different strength, of frequency dependent flame driving behavior. These results indicate that the acoustic property of the nonreactive burner system is the main mechanism responsible for the flame driving behavior. The flame character is important mainly in determining the strength of the flame driving/damping. These results could be elucidated by the fact that the distributions of|v'|/|p'| and .psi./sub p'v'/ for reactive burners are similar to those for the nonreactive burner, respectively. Also, the presence of flames modifies the values, but not the trend, of the frequency dependent |v' |/|p'| and.psi./sub p'v'/, where the modifications depend on the flame equivalence ratio. Results of this research also suggest that the imaginary parts of the nonreactive burner admittance could be used to qualitatively predict the flame driving behavior, which would much simplify the studies of thermo-acoustic instabilities.