[[alternative]]Investigations of flame induced pressure oscillation in a combustor

[[abstract]]本研究實驗與理論探討一長方管中，管壁側向預混火燄燃燒所產生聲波振盪之研究。實驗乃以麥克風及光電管，分別作壓力振盪及火燄輻射振盪之量測。實驗結果顯示，於液態瓦斯﹣空氣混合氣流速約在 8 cm/sec，且當量比值介於 0.64 與 0.81 之間， 預混火燄產生自發性的振盪並誘導出聲波振盪。火燄振盪的主頻率隨著當量比值的減少而降低，而且一般都有多頻率的振盪產生。而火燄週期性不穩定的熱釋放率，誘導出相同頻率的壓力振盪。理論之分析是由數學模式推導出含有源項之波動方程式，配合格林函數之方法求解，來預測壓力振盪之現象。由理論分析與實驗研究皆可發現，火燄激發之壓力振盪的頻率雖然接近實驗管的自然頻率，但會因火燄在管中駐波場位置的不同，其壓力振盪的強度將不同。當火燄位於駐波場最大壓力（反節點）附近時，週期性的火燄振盪將與壓力振盪同相，而壓力振盪將加強。反之，當火燄位於駐波場壓力最小（節點）附近，或壓力振盪頻率遠離實驗管之自然頻率時，火燄振盪將不易激起壓力振盪，造成壓力振盪有被相對減弱的現象。本研究中由理論預測與實驗所得之壓力頻譜相近。[[abstract]]This research is concerned with the experimental and theoretical studies of premixed flame induced pressure oscillatioins in a rectangular combustor. The experimental studies were conducted by using microphone and photomultiplier tube for pressure and flame radiation oscillations measurements, respectively. The results of these studies indicate that the flame exhibits self-excited oscillation and induces pressure oscillations with the air-LPG mixture equivalence ratio ranging between 0.64 and 0.81 in the vincinity of mixture velocity 8 cm/sec. In general, the flame oscillates with multiple frequencies and induces same frequencies of pressure oscillations. In addition, the main frequency of flame oscillation decreases as the equivalence ratio decreases. The theoretical studies were analyzed based on the wave equation with source terms and solved by Green's function to predict the characteristics of the pressure oscillation. From both experimental and theoretical studies, it was found that the presure oscillation can be enhanced or damped by the flame oscillation depending on the frequency of oscillation and the flame location relative to the acoustic field. When the flame is located at the pressure antinode of acoustic field and the oscillating frequencies are close to the natural frequencies of the experimental duct, the pressure oscillatioins are enhanced. On the countrary, when the flame is located at pressure node or the oscillating frequencies are away from the natural frequencies of the duct, the pressure oscillations are damped. The experimental obtained pressure oscillation spectra are in good agreement with the theoretical predictions.[[booktype]]紙