燃燒理論基礎(chǔ)第六章

1、燃燒理論基礎(chǔ)課件第六章 氣體燃料的噴射與燃燒（Jet and combustion of gaseous fuels）汽車與交通工程學(xué)院王維強(qiáng)主要內(nèi)容 6.1 概述 6.2 無燃燒的氣體平面射流 6.3 軸對稱氣體的自由射流 6.4 靜止空氣中軸對稱射流的燃燒 6.5 受限射流的擴(kuò)散火焰l多組分系統(tǒng)中某些組成物的濃度梯度(或密度梯度)會引起分子擴(kuò)散傳質(zhì)，同時流體的流動也會引起對流傳質(zhì)。l當(dāng)流體從噴管(或噴口)噴出時，它和環(huán)境流體相互作用而形成射流。l由于射流和環(huán)境介質(zhì)之間的摩擦而引起了動量交換，環(huán)境的介質(zhì)越過射流邊界而被引射出來。 l 有射流必有引射，引起了動量交換和能量交換。 l工程上廣泛應(yīng)

2、用的氣體和液體燃燒有預(yù)混合的，有擴(kuò)散燃燒。l當(dāng)燃燒揮發(fā)性高，噴射壓力高，在高溫高壓的環(huán)境中，可近似氣體射流。6.1 概說Jet Flames Simple Jet Flames 簡單射流火焰 Piloted Jet Flames 引導(dǎo)射流火焰 Bluff Body Flames 內(nèi)置鈍體火焰 Swirl Flames 旋流火焰Simple Jet FlamesCO/H2/N2 Jet FlamesSandia/ETH-ZurichFuel composition: 40% CO, 30% H2, 30% N2 Stoichiometric mixture fraction: Fstoic =

3、0.295Flame length: Lstoic 47dReynolds number: 16,700 (same for both flames)Flame chnA: Nozzle inner diameter, d = 4.58 mm; Outer diameter = 6.34 mm; Ujet=76 m/sFlame chnB: Nozzle inner diameter, d = 7.72 mm; Outer diameter = 9.46 mm; Ujet=45 m/sCoflow velocity: 0.75 m/s Simple Jet Flames (contd)CH4/

4、H2/N2 Jet Flames DLR-Stuttgart/TU-Darmstadt/SandiaNozzle: d=8.0 mm inner diameter, tapered to a sharp edge.Fuel composition: 22.1% CH4, 33.2% H2, 44.7% N2 Stoichiometric mixture fraction: Fstoic = 0.167Flame DLR_A: Ujet=42.2 m/s; Re=15200Flame DLR_B: Ujet=63.2 m/s; Re=22800Coflow: 0.3 m/s, 292K, 0.8

5、% mole fraction H2O Simple Jet Flames (contd) Rayleigh and PLIF images of CH4/H2/N2 Jet Flames DLR-Stuttgart/TU-Darmstadt/SandiaPiloted Jet Flames Piloted CH4/Air Jet Flames Sandia/TUDDimensions: Nozzle diameter = 7.2mm; Pilot diameter = 18.2mmMain jet: 25% CH4, 75% air; Fstoic = 0.351, Lvis 67dReyn

6、olds numbers: C-13400, D-22400, E-33600, F-44800Pilot: The pilot flame burns a premixture of C2H2, H2, air, CO2, and N2 having nominally the same equilibrium composition and enthalpy as CH4/air. The pilot is operated lean, phi = 0.77, and the flow rate is scaled in the four turbulent flames to maint

7、ain the pilot at 6% of the power of the main flame. Sydney Burner Geometry Sydney Burner GeometryPiloted Jet Flames (contd)Delft III Piloted Natural Gas FlameDelft Technical University/SandiaDimensions: Nozzle diameter = 6 mm; Primary air annulus diameter = 45 mmMain jet: Natural gas (approx. 81% CH

8、4, 14% N2)Pilot: The pilot burns a premixture of C2H2/H2/air. View pilot image.Flow Conditions: Ujet=21.9 m/s, Uann=4.4 m/s, Ucoflow=0.3 m/sPilot imageJet flame imageBluff Body Flames CH4/H2 Jet FlamesU Sydney/SandiaSwirl FlamesTECFLAM Swirl FlamesSandia/ETH-ZurichBurner and chamber geometry: Fuel a

9、nnulus: di = 20 mm, do = 26 mm Air annulus: Di = 30 mm, Do = 60 mm Chamber size: Lc = 1200 mm, Dc = 500 mm Outflow annulus: Diout = 470 mm, Doout = 500 mm Fuel jet: Natural Gas (no swirl) Air jet: Coflow (swirl) TECFLAM Burner GeometryS09f animation 圓形射流：以圓截面噴口流出，對稱于射流軸向，二維。 環(huán)形射流：在一次射流周圍引入二次空氣。 平面射流

10、：噴口為狹窄的縫隙。 交叉射流：以某一角度貫穿入主流的射流。射流形式射流形式(由噴口幾何結(jié)構(gòu)) 自由射流：無窮大均勻空間，射流不受周圍邊界的約束干擾。 受限射流：受介質(zhì)邊界尺寸和邊界摩擦約束，會影響到射流狀態(tài)（運(yùn)動、混合）。射流形式射流形式(由周圍介質(zhì)的運(yùn)動狀態(tài))Free JetsTurbulent Free JetsMomentum Jets Buoyant JetsSchlieren Photograph of the Jet Flow射流的紋影照片 射流場的描述方法u/um,um為最大軸線速度u/ui,ui為出口速度等6.2 無燃燒的氣體平面射流1假定：假定：（1）為穩(wěn)態(tài)的自由射流； （圖66）（2）取無限長狹縫，寬度為狹縫中的一個單位長度；（3）視絕熱無損失（摩擦、滲漏）；（4）高溫高壓的噴射氣體與靜止環(huán)境介質(zhì)特性相同。噴口狀態(tài)為 、 和 。軸線上（ 0 x 0.5時，便出現(xiàn)供氧過?；鹧?。 BurkSchumann用理論解求得的層流火焰形狀與實(shí)際火焰的形態(tài)相當(dāng)接近。 貝克-舒曼火焰實(shí)驗(yàn) 射流擴(kuò)散火焰可以由本生燈試驗(yàn)系統(tǒng)關(guān)閉一次空氣而得