實驗研究密度比效應對紊流火焰速率之影響;Experimental Investigation of Effect of Density Ratio on Turbulent Flame Speed

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Title:	實驗研究密度比效應對紊流火焰速率之影響;Experimental Investigation of Effect of Density Ratio on Turbulent Flame Speed
Authors:	李文義;LI,WUN-YI
Contributors:	能源工程研究所
Keywords:	高溫預混燃燒;弱紊流預混燃燒;密度比效應;流力(Darries-Landau)不穩定性;指狀結構不穩定性
Date:	2015-11-11
Issue Date:	2016-01-05 17:57:46 (UTC+8)
Publisher:	國立中央大學
Abstract:	數十年來，紊流燃燒率w ̇_t，它可由火焰(位移)速率SF或燃燒(消耗)速度uc來代表，一直是實驗研究預混燃燒的重點。其中，有一重要的燃氣特性，即密度比= u/b(下標u和b分別代表未燃燃氣和已燃生成物)，當進行參數化SF或uc之實驗數據時，的效應在實驗上幾乎從未被研究過。由預混紊流火焰基本了解的觀點來看，密度比對燃燒率的影響是有其重要的價值，而目前僅有少數數值和理論研究有討論此一密度比效應，急需一目標特定的實驗來驗證。本論文的目標，即是實驗驗證密度比對燃燒率的影響。我們使用特別準備的燃氣(化學計量甲烷/空氣燃氣)，它結合了預熱和稀釋，使得在常溫條件下之燃氣與在高溫稀釋條件下之燃氣，兩者可維持相同的層流燃燒速率但彼此具有明顯不同的密度比，藉由量測其紊流火焰速率，來實驗研究對w ̇_t之影響效應。實驗於中央大學已建立之雙腔體十字型燃燒器並加上新設計之加熱器的設施中進行，它可產生近似等向性紊流和一具均勻高溫環境。從統計球狀擴張化學計量甲烷/空氣火焰，其在不同的方均根紊流擾動速度uʹ所獲得的實驗數據顯示，當在低u′⁄S_L <1條件下，火焰速率隨密度比增加而相當微弱地增加，而在適度u′⁄S_L >1條件下，火焰速率與密度比無關。最後，紊流火焰速率在u′⁄S_L =0.4時所量測到的數值，在所有不同條件下(預熱和稀釋)皆不大於層流燃燒速率。;Turbulent combustion rate w ̇_t characterized using either flame (displacement) speed SF or burning (consumption) velocity uc was in the focus of experimental research into premixed combustion for many decades. There is an important mixture characteristic, i.e. the density ratio σ=ρ_u⁄ρ_b , that has yet been rarely used when parameterizing experimental data on SF or uc. While the influence of the density ratio on the combustion rate is of great interest for basic understanding of premixed turbulent flames and was addressed in a couple of numerical and theoretical studies, this issue is still waiting for a target-directed experimental investigation. The goal of this thesis is to fill this gap by measuring turbulent flame speeds in mixtures that have been specially prepared by combining preheating and dilution of unburned reactants in order to retain the laminar flame speed unchanged, but substantially change the density ratio. The experiments are conducted in a dual-chamber explosion facility that has been extensively used to measure propagation speeds of expanding turbulent flames at National Central University. The facility with new modifications for heating consisted of a large inner 3D cruciform burner situated within a huge outer chamber, capable of generating near-isotropic turbulence and producing a uniform high-temperature environment. Experimental data obtained from statistically spherical expanding stoichiometric methane-air flames at various r.m.s. turbulent velocities u′ show that the flame speed is very weakly increased by the density ratio at low u′⁄S_L <1 and is independent of the density ratio at moderate u′⁄S_L >1. Moreover, turbulent flame speeds measured at u′⁄S_L = 0.4 are not larger than the laminar flame speeds in all cases investigated.
Appears in Collections:	[Energy of Mechatronics] Electronic Thesis & Dissertation

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