复习：层流火焰速度的测量方法 ■稳态火焰法 口平面火焰√ 口本森灯火焰√ 口对型流火焰√/ ■非稳态火焰法 口管内传播火焰X 口球形传播火焰（定容）VW 口球形传播火焰（定压）√√ 口肥皂泡法X ) 《燃烧学基础》6，层流预混火焰 陈正(z@pku.edu.cn)13 点火与火焰传播 Effect of Timing on Engine Torque R Ignition time(~10ms) Da-Flow residence tim (m Challenges: Ignition time,Ignition energy ■Flame stabilization Scramjet engine with hydrocarbon fuels ■Complete combustion 《燃烧学基础》6，层流预混火焰 陈证(cz@pku.edu.cn)14
澦䏝ׁक澧 ͧࡗقஓ䍡 ୟࠔ I`&VQ[KJ[IT ࡄݱଞ࡚ࣩڅૻ䍡ࡗق͵Эו ࡄ㓆䍡 ऻ 䍡ٴ 䍥䍡ߺޯ 䍡ࡗֹت ࡄ㓆䍡 ஂऻ 䍡ݏॡӃѭ ؟ؓ䍡ݏѭڤࣁ Ըؓ䍡ݏѭڤࣁ ࡄࡆ剘䤝 Figures from Egolfopoulos et al., Prog. Energy Comb. Sci. 43 (2014). ; ; Qin and Ju (2005) Equivalence ratio, Laminar flame speed, SL (cm/s) 0.6 0.8 1 1.2 1.4 0 10 20 30 40 A-SURF (2009) Taylor (1991) Gu et al. (2000) Rozenchan et al. (2002) " CH4/air 䍥䍡ߺޯ 䍡ࡗֹت ࡄ㓆䍡 䍡ݏॡӃѭ ; 澦䏝ׁक澧 ͧࡗقஓ䍡 ୟࠔ I`&VQ[KJ[IT ݏѭ䎯䍡Љ䍡 NissanCVT Scramjet engine with hydrocarbon fuels Ignitiontime(~10ms) Flowresidencetime(~1ms) Da= >>1 Challenges: Ignition time, Ignition energy Flame stabilization Complete combustion Mach38 Da= ch 38
点火 What happens during spark ignition? 3.5μs 1004S 2004s 3004s (b)H2 (50%)-air.E=3.0Emin 3.5μs 504s 100μs 150μs (c)H2 (30%)-air.E =1.5Emin R.Ono,T.Oda Combustion and Flame 152(2008)69-79 《燃烧学基础》6，层流预混火焰 陈正(a@pku.edu.cn15 点火 Schematics of the flame formation process T-10.000K S.Bane,2010 《燃烧学基础》6，层流预混火焰 陈证(z@pku.edu.cn)16
澦䏝ׁक澧 ͧࡗقஓ䍡 ୟࠔ I`&VQ[KJ[IT 䎯䍡 What happens during spark ignition? R. Ono, T. Oda / Combustion and Flame 152 (2008) 69–79 澦䏝ׁक澧 ͧࡗقஓ䍡 ୟࠔ I`&VQ[KJ[IT 䎯䍡 S. Bane, 2010 Schematics of the flame formation process
点火 TIME IGNITION EXTINCTION 点火 1.Breakdown phase plasma electrical temp 5k -60000K 102 101 2.Arc phase(spark 100 10 10 10 channel) 103 Plasma temp.~6000 K 3.Initial flame kernel Adiabatic flame temp. 102 ho 103 -2300K R.Maly,M.Vogel /Proc.Combust.Inst.(1976) 《燃烧学基础》6，层流预混火焰 陈正(a@pku.edu.cm)18
澦䏝ׁक澧 ͧࡗقஓ䍡 ୟࠔ I`&VQ[KJ[IT 䎯䍡 Knon et al., Combust. Flame 27 (1976) 85-98 澦䏝ׁक澧 ͧࡗقஓ䍡 ୟࠔ I`&VQ[KJ[IT 䎯䍡 R. Maly, M. Vogel / Proc. Combust. Inst. (1976) 1. Breakdown phase plasma electrical temp. ~60000 K 2. Arc phase (spark channel) Plasma temp. ~ 6000 K 3. Initial flame kernel Adiabatic flame temp. ~ 2300 K
点火 What is flame initiation CH./ain uccessful ignition Time Why flame initiation Flame initiation is important to 89 .The control of fire safety and explosior .The ignition control in internal combustion engines The understanding of flame extinction and of tu rbulent combustio (Figs from internet) 《燃烧学基础》6，层流预混火焰 陈证(cz@pku.edu.cn)19 最小点火能 ■最小点火能(Minimum Ignition Energy,MIE)的估计 ■最小可持续向外传播的火焰核(flame kernel))半径近似为火焰厚度6 ■火焰厚度取决于化学反应放热与向预热区热传导间的平衡： c,云盟→Ac,- →6=ps ■点火能近似为将火焰核的温度由上升到T所需要的热量： E-音ipc,亿-T) 4π(T-T) 3 (p.C)2S ■压力影响：S,~pw1p~P→E~p32 ■航空发动机高空二次点火难题 ■初始温度的影响：T。越高则S,越高，从而MIE越低 10 ■当量比的影响：当量比越接近于1.0则S,越高，从而MIE越低 R.Ono et al.(2007) 《燃烧学基础》6，层流预混火焰 陈正(z@pku.edu.cn)20
澦䏝ׁक澧 ͧࡗقஓ䍡 ୟࠔ I`&VQ[KJ[IT 䎯䍡 Flame initiation is important to The control of fire safety and explosion Why flame initiation ? The ignition control in internal combustion engines The understanding of flame extinction and re-ignition of turbulent combustion Successful Ignition Unsuccessful ignition Flame radius Time What is flame initiation ? Q ? CH4/air (Figs from internet) ant to Fl a 澦䏝ׁक澧 ͧࡗقஓ䍡 ୟࠔ I`&VQ[KJ[IT 䎯䍡ৗسޣ سޣ䎯䍡ৗ3OTOS[S /MTOZOUT +TKXM_ 3/+ࣩѲਗ਼ سޣՔܕডզטѭࣩݏ䍡ߟLRGSK QKXTKRԠګѶН䍡Իڅ Ś ͵ٴࣩج䏣Љզஓ䏣ԙ䏣ѭݚڀՅՇӏиԖڅԻ䍡 䎯䍡ৗѶНذ䍡࣒څࡴࣩߟ ]:ІԞӰ:H ےੌࣩ䏣ଞ͵ ԸԂڦտ͵ ৰीՆԇளीзࠊ䎯䍡୰ங ӫڦࣩڅࡴտ͵:ભளӨ92 ભளͧёু3/+ભѹ ڡଞࠢڦࣩտ͵ڡଞࠢભܯиӨ92 ભளͧёু3/+ભѹ b u u L P b u T T S C T T ( ) u SLCP u P L b u u P b u C S T T E C T T ( ) ( ) ( ) min # # $ / ~ n SL P ~ P / min ~ n E P R. Ono et al. (2007) ( ) dx dT dx d dx dT mCP ے H:ІԞӰ:[ ࣒څ b u L P b u Tb Tu LCP Tb Tu ) u P b u ( uCP (Tb ) Tu #
最小点火能 ■理论推导：最小/临界火焰核半径R近似为火焰厚度6 ■临界着火条件：化学反应释放热量的速率等于热传导出去热量的速度，即： “火始核外为纯热传号过程及边界条件为：子公心：)-0 T(r=R)=T Tr→o)=T ■因此温度分布为：T)=T+R(亿，一刀)， 4 ■代入临界着火条件得： g,@P写成=4R,(亿-T) 4,0,p-pC(T,-T.)S2la a=Al(pC) Re~6=alS E-成.c-)n.c,-) 《燃烧学基础》6，层流预混火焰 陈正(z@pku.edu.cn)2i 预燃室点火 Time=0.00003 Combustion of Premixed Iso octane-Air Mixtures in a Pre- chamber-Main-chamber system. From internet Mastorakos et al.,2017SAE 《燃烧学基础》6，层流预混火焰 陈正(a@pku.edu.cm)2
澦䏝ׁक澧 ͧࡗقஓ䍡 ୟࠔ I`&VQ[KJ[IT 䎯䍡ৗسޣ Ś څԻ䍡 ѶН) 8 ګԠߟ䍡ࣙКسޣ͵جܱࣂ ͵ԮuڅૻࣩӞԽ䏣ଞجи䏣ѭॗࢴૻࣩ䏣ଞݚଚڀՅԖ͵ѝअ䍡ࣙК 䍡טߟНআ䏣ѭجसՂࣙѝН͵ ͵Ӣ١Нڅࡴࠕ֛ ͵ڰѝअ䍡ࣙіҴК C F F r R C C dr dT q R R # # ( ) dr dT r dr d r RC Tb T(r ) Tu T(r !) T r T R T T r u C b u ( ) ( )/ ( ) q F F #RC #RC Tb Tu ~ ( ) / q F F CP Tb Tu SL /( ) CP RC SL ~ / ( ) ( ) Emin #RC uCP Tb Tu $ # uCP Tb Tu RC ࣙѝН͵ dr d r r u C b u R (T T )/ u RC Tb Tu q F F #RC 澦䏝ׁक澧 ͧࡗقஓ䍡 ୟࠔ I`&VQ[KJ[IT ஓ؛䎯䍡 Combustion of Premixed Iso octane-Air Mixtures in a Prechamber-Main-chamber system. From internet Mastorakos et al., 2017SAE