| 摘要: | 本論文使用奈秒重覆脈衝放電(Nanosecond Repetitively Pulsed Discharges, NRPD)，針對氨氣/空氣混合燃氣在當量比 = 1、固定電極間距dgap = 2 mm及重覆脈衝頻率PRF = 40 kHz之條件下，量測最小引燃能量(Minimum Ignition Energy, MIE)隨均方根擾動速度(u′)之變化關係，MIE為具50%引燃機率的能量。引燃實驗在一大型高壓雙腔體之十字型預混紊流燃燒器中進行，其腔體正中心處設有一對不銹鋼之尖端電極以進行放電，且在大水平圓管腔體兩側各裝有一風扇，可透過反向旋轉特製扇葉在中心處產生一近似等向性紊流場。首先，在層流條件下，使用不同當量比( = 0.9、1.0和1.1)來進行層流MIE (MIEL)之量測，結果顯示，MIEL = 80.4, 72.6 和71.8 mJ 在 = 0.9, 1.0和1.1，即MIEL值會隨著值的增加而下降。再者，我們選擇 = 1.0的條件，進行紊流MIE (MIET)之量測，我們找到一MIE轉變，即在u′小於一臨界u′c ≈ 1 m/s時，MIET值會隨著u′的增加而緩慢上升，但當u′ > u′c時，MIET值則會隨u′值增加而急遽攀升。同樣地，本研究也有找出氨氣之正規化MIET/MIEL與火核反應區Péclet數(Pe = u′k/RZ)之關係，其中k為Kolmogorov長度尺度，RZ (≈ SLδRZ)為反應區熱擴散係數，SL為層流火焰速度，δRZ為層流火焰厚度，並發現其臨界Pec ≈ 4.4，與本實驗室之前量測到的甲烷/空氣(Pec ≈ 4.5)及汽油替代燃料(Pec ≈ 4.2)之結果接近。最後，在電極間距dgap = 1 mm時，即使使用數千個NRPD脈衝（總能量約為2 J），也無法成功引燃在化學計量之氨氣/空氣混合燃氣。前述結果，對以氨為燃料正發展中發電用之燃氣輪機的引燃，應有所助益。;This thesis measures the minimum ignition energy (MIE) of the stoichiometric ammonia/air mixture as a function of root-mean-square (r.m.s) turbulent fluctuation velocities (u′). Using nanosecond repetitively pulsed discharges (NRPD) via a pair of stainless-steel electrodes with sharp ends at a fixed inter-electrode gap (dgap = 2 mm) and at a fixed pulsed repetitive frequency (PRF = 40 kHz). Ignition experiments are conducted in a dual-chamber, fan-stirred cruciform burner capable of generating near-isotropic turbulence. First, values of laminar MIE (MIEL) are measured at three different equivalence ratios ( = 0.9, 1.0 and 1.1 );MIEL decreases with increasing , MIEL = 80.4, 72.6 and 71.8 mJ at = 0.9, 1.0 and 1.1, respectively。Second, at the selected = 1.0, a MIE transition is found. When u′ is less than a critical value of u′c ≈ 1 m/s, turbulent MIE (MIET) only increases gradually with increasing u′. But when u′ > u′c, a drastic increase of MIET is observed. We also find a function of normalized MIET/MIEL and Péclet number (Pe = u′k/RZ) for ammonia/air mixture, where k is the Kolmogorov length scale and the reaction zone thermal diffusivity RZ (≈ SLδRZ);SL is the laminar burning velocity and δRZ is the laminar flame thickness. It is found the critical Pec occurs at a value of about 4.4 which is very close to the methane/air mixture (Pec ≈ 4.5) and the primary reference automobile fuel/air mixture (Pec ≈ 4.2) our laboratory done before. Finally, when dgap = 1 mm, even using several thousands of NRPD pulses (total energy ~ 2J) cannot ignite the ammonia/air mixture at = 1.0 and at PRF = 40 kHz. These results may be useful to our understanding of ignition for the developing ammonia gas turbines for electricity generation. |
