填充多孔纤维的微细通道内CH_4/空气火焰的稳燃机理
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摘要
在微细通道内填充高孔隙率(0.94)、低导热系数(0.3,W/(m·K))的陶瓷纤维能够有效拓宽驻定火焰波发生的速度范围.为了揭示其稳燃机理,本文进行了数值模拟,结果表明:增大纤维导热系数或者减小孔隙率时,驻定火焰出现的速度范围缩小,而且火焰对上游未燃气体的预热量和向下游的散热量都将增大,但是后者明显高于前者.因此,微细通道内填充纤维型多孔介质后驻定火焰范围变宽的根本原因在于其具有很低的导热系数和很高的孔隙率,有效地减少了火焰向下游传递的热量,提高了火焰稳定性.
The velocity limits of stationary flame can be effectively expanded by filling ceramic fibers with high porosity(0.94)and low thermal conductivity(0.3,W/(m·K))in mesoscale channels.To reveal the underlying mechanisms,numerical simulation was conducted.The results show that,by increasing the thermal conductivity or decreasing the porosity of ceramic fibers,the velocity range of stationary flames shrinks noticeably. Quantitative analysis demonstrates that the heat recirculation to upstream mixture and the heat transfer downstream are both enhanced,but the latter is more pronounced than the former.In conclusion,the reasons for the stronger flame stability of the mesoscale channel filled with fibrous porous media are the high porosity and low thermal conductivity of ceramic fibers,which can significantly reduce the heat dissipation from the flame to downstream gases.
The velocity limits of stationary flame can be effectively expanded by filling ceramic fibers with high porosity(0.94)and low thermal conductivity(0.3,W/(m·K))in mesoscale channels.To reveal the underlying mechanisms,numerical simulation was conducted.The results show that,by increasing the thermal conductivity or decreasing the porosity of ceramic fibers,the velocity range of stationary flames shrinks noticeably. Quantitative analysis demonstrates that the heat recirculation to upstream mixture and the heat transfer downstream are both enhanced,but the latter is more pronounced than the former.In conclusion,the reasons for the stronger flame stability of the mesoscale channel filled with fibrous porous media are the high porosity and low thermal conductivity of ceramic fibers,which can significantly reduce the heat dissipation from the flame to downstream gases.
引文
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[2]Waitz I A,Gauba G,Tzeng Y S.Combustion for micro gas turbine engines[J].ASMS Journal of Fluids Engineering,1998,20(1):109-117.
[3]Spadaccini C M,Peck J,Waitz I A.Catalytic combustion systems for microscale gas turbine engines[J].Journal of Engineering for Gas Turbines and Power,2007,129(1):49-60.
[4]Miesse C M,Masel R I,Jensen C D,et al.Submillimeter-scale combustion[J].AICh E Journal,2004,50(12):3206-3214.
[5]Daou J,Matalon M.Flame propagation in Poiseuille flow under adiabatic conditions[J].Combustion and Flame,2001,124(3):337-349.
[6]Daou J,Matalon M.Influence of conductive heat-losses on the propagation of premixed flames in channels[J].Combustion and Flame,2002,128(4):321-339.
[7]Daou J,Dold J,Matalon M.The thick flame asymptotic limit and Damk?hler's hypothesis[J].Combustion Theory and Modelling,2002,6(1):141-153.
[8]Ju Y,Xu B.Effects of channel width and Lewis number on the multiple flame regimes and propagation limits in mesoscale[J].Combustion Science and Technology,2006,178(10/11):1723-1753.
[9]Maruta K,Takeda K,Ahn J,et al.Deutschmann,extinction limits of catalytic combustion in microchannels[J].Proceedings of the Combustion Institute,2002,29(1):957-963.
[10]Kim N I,Kato S,Kataoka T,et al.Flame stabilization and emission of small Swiss-roll combustors as heaters[J].Combustion and Flame,2005,141(3):229-240.
[11]Kim N I,Aizumi S,Yokomori T,et al.Development and scale effects of small Swiss-roll combustors[J].Proceedings of the Combustion Institute,2007,31(2):3243-3250.
[12]Yang W,Chou S,Shu C,et al.Combustion in microcylindrical combustors with and without a backward facing step[J].Applied Thermal Engineering,2002,22(16):1777-1787.
[13]万建龙,范爱武,刘毅,等.固体材料对微型钝体燃烧器吹熄极限的影响[J].化工学报,2014,65(3):1012-1017.Wan Jianlong,Fan Aiwu,Liu Yi,et al.Effects of solid material on blow-off limit in micro bluff body combustor[J].CIESC Journal,2014,65(3):1012-1017(in Chinese).
[14]卫尧,匡龙,薛宏,等.微型热光电系统多孔介质燃烧器的数学模拟[J].河南科技大学学报:自然科学版,2005,26(4):30-32.Wei Yao,Kuang Long,Xue Hong,et al.Simulation of porous medium burner in micro-thermal photoelectric system[J].Journal of Henan University of Science and Technology:Natural Science,2005,26(4):30-32(in Chinese).
[15]张会峰,潘剑锋,唐爱坤,等.材料和喷口直径对多孔介质微燃烧的影响[J].小型内燃机与摩托车,2009,38(6):26-30.Zhang Huifeng,Pan Jianfeng,Tang Aikun,el at.The effects of material and nozzle diameter on porous media micro-combustor[J].Small Internal Combustion Engine and Motorcycle,2009,38(6):26-30(in Chinese).
[16]陈金星,李君,李擎擎.多孔介质微燃烧器的稳燃范围的数值研究[J].燃烧科学与技术,2017,23(3):231-235.Chen Jinxing,Li Jun,Li Qingqing.Numerical study on stability limits of combustion in micro-combustors with porous medium[J].Journal of Combustion Science and Technology,2017,23(3):231-235(in Chinese).
[17]Yang H,Minaev S,Geynce E,et al.Filtration combustion of methane in high-porosity micro-fibrous media[J].Combustion Science and Technology,2009,181(4):654-669.
[18]Pedras M H J,de Lemos M J S.Macroscopic turbulence modeling for incompressible flow through undeformable porous media[J].International Journal of Heat and Mass Transfer,2001,44(6):1081-1093.
[19]Westbrook C K,Dryer F L.Simplified reaction mechanisms for the oxidation of hydrocarbon fuel in flames[J].Combustion Science&Technology,1981,27(1/2):31-43.
[20]Holman J P.Heat Transfer[M].New York:Mc GrawHill,2002.
[21]Fluent Incorporated.Fluent User’s Guide[M].Lebanon NH:Fluent Incorporated,2010.