小尺度燃烧器壁面热性能对火焰稳定性的影响
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摘要
从调整小型燃烧器壁面热性能的角度出发,对改善其稳燃性能进行了研究,共进行了两个实验.第1个实验采用多孔介质燃烧技术,比较研究了不同导热率的壁面材料(硅与石英)对燃烧器稳燃性的影响.结果发现,尽管两种材料燃烧器有着相同的低速极限,但是高导热率的硅燃烧器比石英燃烧器有着更大的高速极限,使火焰能够稳定在多孔介质材料上而不被吹出.第2个实验探索了各向异性材料热解石墨燃烧器的性能,作为对比,对各向同性的不锈钢316常规材料燃烧器也进行了研究.由于壁面被增强的流向导热及被减弱的法向热损失,热解石墨与各向同性的不锈钢相比,稳燃极限扩大,有着更大的稳燃区间.
In this study, we performed two sets of experiment to investigate conditions that would improve the flame stability of small-scale combustors by adjusting the thermal properties of walls. In the first experiment, we used porous media combustion technology to study the effects of the thermal conductivities of different wall materials(silicon and quartz) on the flame stability. We found that although two types of wall materials had the same low-velocity limit, the silicon combustor with higher thermal conductivity had a higher high-velocity limit than the quartz combustor, which stabilized the flame on porous media to prevent blow-off extinction. In the second experiment, we investigated the performance of a pyrolytic graphite combustor with respect to its thermally orthotropic properties. For comparison, we also studied the performance of the conventional isotropic material stainless steel 316. The results showed that the pyrolytic graphite combustor exhibited wider flame-stability limits than the stainless steel combustor, due to its enhanced stream-wise heat conduction and reduced span-wise heat loss.
In this study, we performed two sets of experiment to investigate conditions that would improve the flame stability of small-scale combustors by adjusting the thermal properties of walls. In the first experiment, we used porous media combustion technology to study the effects of the thermal conductivities of different wall materials(silicon and quartz) on the flame stability. We found that although two types of wall materials had the same low-velocity limit, the silicon combustor with higher thermal conductivity had a higher high-velocity limit than the quartz combustor, which stabilized the flame on porous media to prevent blow-off extinction. In the second experiment, we investigated the performance of a pyrolytic graphite combustor with respect to its thermally orthotropic properties. For comparison, we also studied the performance of the conventional isotropic material stainless steel 316. The results showed that the pyrolytic graphite combustor exhibited wider flame-stability limits than the stainless steel combustor, due to its enhanced stream-wise heat conduction and reduced span-wise heat loss.
引文
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[2]Kaisare N S,Vlachos D G.A review on microcombustion:Fundamentals,devices and applications[J].Progress in Energy and Combustion Science,2012,38(3):321-359.
[3]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.
[4]Wan J,Fan A,Maruta K,et al.Experimental and numerical investigation on combustion characteristics of premixed hydrogen/air flame in a micro-combustor with a bluff body[J].International Journal of Hydrogen Energy,2012,37(24):19190-19197.
[5]Wan J,Fan A,Liu Y,et al.Experimental investigation and numerical analysis on flame stabilization of CH4/air mixture in a mesoscale channel with wall cavities[J].Combustion and Flame,2015,162(4):1035-1045.
[6]Li J,Chou S K,Li Z W,et al.Experimental investigation of porous media combustion in a planar microcombustor[J].Fuel,2010,89(3):708-715.
[7]Ning D,Liu Y,Xiang Y,et al.Experimental investigation on non-premixed methane/air combustion in Y-shaped meso-scale combustors with/without fibrous porous media[J].Energy Conversion and Management,2017,138:22-29.
[8]Kang X,Gollan R J,Jacobs P A,et al.Suppression of instabilities in a premixed methane-air flame in a narrow channel via hydrogen/carbon monoxide addition[J].Combustion and Flame,2016,173:266-275.
[9]Veeraragavan A,Cadou C P.Flame speed predictions in planar micro/mesoscale combustors with conjugate heat transfer[J].Combustion and Flame,2011,158(11):2178-2187.
[10]Federici J A,Vlachos D G.A computational fluid dynamics study of propane/air microflame stability in a heat recirculation reactor[J].Combustion and Flame,2008,153(1):258-269.
[11]Kang X,Veeraragavan A.Experimental demonstration of a novel approach to increase power conversion potential of a hydrocarbon fuelled,portable,thermophotovoltaic system[J].Energy Conversion and Management,2017,133:127-137.
[12]Norton D G,Vlachos D G.Combustion characteristics and flame stability at the microscale:a CFD study of premixed methane/air mixtures[J].Chemical Engineering Science,2003,58(21):4871-4882.
[13]Kang X,Veeraragavan A.Experimental investigation of flame stability limits of a mesoscale combustor with thermally orthotropic walls[J].Applied Thermal Engineering,2015,85:234-242.
[14]Singh A P,Kishore V R,Yoon Y,et al.Effect of wall thermal boundary conditions on flame dynamics of CH4-air and H2-air mixtures in straight microtubes[J].Combustion Science and Technology,2017,189(1):150-168.
[15]Jiang L Q,Zhao D Q,Guo C M,et al.Experimental study of a plat-flame micro combustor burning DME for thermoelectric power generation[J].Energy Conversion and Management,2011,52(1):596-602.
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