貧油丙烷於層流和紊流條件下之最小引燃能量量測; measures of lean propane-air on laminar and turbulent minimum ignition energies

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Title:	貧油丙烷於層流和紊流條件下之最小引燃能量量測;measures of lean propane-air on laminar and turbulent minimum ignition energies
Authors:	鍾華榮;Hua-jung Chung
Contributors:	機械工程研究所
Keywords:	輻射熱損失效應;最小引燃能量;預混紊流燃燒;minimum ignition energy;radiation heat losses;premix turbulent combustion
Date:	2011-08-27
Issue Date:	2012-01-05 12:34:17 (UTC+8)
Abstract:	本研究針對貧油丙烷空氣預混燃氣，定量量測其最小引燃能量(minimum ignition energy, MIE)，研究目標在於測試貧油丙烷預混燃氣是否會如本實驗室先前使用甲烷燃氣時也存在一火花引燃轉折(ignition transition)現象。實驗於一大十字型預混紊流燃燒器(Shy et al. 2010)執行，在水平圓管兩端各配置一組三相十匹馬力馬達和特製風扇，由此一對反向旋轉風扇所產生之氣流並各經特製之空孔板，可在十字型燃燒器中央區域產生一150 × 150 × 150 mm3之近似等向性紊流場，其均方根紊流擾動速度u?值可高達8 m/s。我們使用高電壓脈衝引燃系統和Phantom v310高速攝影機，來量測MIE值和火核發展影像。結果顯示MIE值會隨紊流強度(u'/SL)之增加而逐漸增加，但當u?/SL值大於某臨界值時，MIE值會劇烈地增加，SL為層流燃燒速度。是故，使用丙烷燃氣同樣出現引燃轉折現象，轉折現象是與紊流強度有密切關係，此結果也顯示預混紊流燃燒確實存在不同燃燒型態。本研究另一目標為探討輻射熱損失效應對MIE值之影響，我們個別地添加輻射熱損失效應很強之二氧化碳和很弱之氮氣至貧油甲烷空氣預混燃氣(當量比phi = 0.7)，以稀釋燃氣配比為59%CH4/41%CO2和44%CH4/56%N2，來使兩者具有同樣之SL = 0.1 m/s及絕熱火焰溫度約為1750 K，來進行實驗量測並作比對。結果顯示輻射熱損失效應對MIE值有一定程度的影響，在固定u'/SL ≈ 28時，比較具高輻射熱損失之CO2添加物案例和添加無輻射熱損失之N2案例，其MIE值差異約7%。本研究成果對火花點火引擎和燃氣渦輪機引燃系統之設計有重要之助益。 This thesis measures quantitatively the minimum ignition energy (MIE) of propane-air pre-mixtures at an equivalence ratio (phi) of 0.7, in order to examine the existence of ignition transition that has been found in methane-air pre-mixtures. The experiments are carried out in a stainless-steel cruciform turbulent premixed combustion facility (Shy et al. 2010), including a pair of the same 10-HP motors with the fans and perforated plates at the end of the horizontal vessel. A region of near-isotropic turbulence, roughly 150 × 150 × 150 mm3, can be created in the central area between two perforated plates, where the rms turbulent fluctuation velocity u' ≈ 8 m/s. In order to acquire MIE and flame kernel images by using the high-voltage pulse discharge system and the high-speed CMOS camera (phantom v310) respectively. Before the critical value of turbulent intensity (u'/SL), MIE only increases gradually with u'/SL, but when u'/SL is greater than some critical value, the increases of MIE suddenly becomes drastic. Here SL is laminar flame speed. The phenomena also exist by using the propane-air mixture. It has proved that the ignition transition is related to the turbulent intensity, demonstrating the existence of different flame types in turbulence. On the other hand, another central idea of this thesis is that MIE are characterized by radiation heat losses (RHL), using the carbon dioxide with strong RHL (59%CH441%CO2) and the nitrogen with weak RHL (44%CH456%N2) are added individually to methane-air pre-mixtures (phi = 0.7), where the diluted mixture have similar SL = 0.1 m/s and adiabatic flame temperature (Tad ≈ 1750 K). Due to the effect of RHL, the difference value of MIE between the strong RHL CO2 case and the weak RHL N2 case is about 7 % at u'/SL ≈ 28. These findings can be applied to the ignition system design of engines and gas turbines.
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