An analysis of sub-limit flame dynamics using opposite propagating flames in mesoscale channels

Ju, Yiguang; Choi, Chun W.

doi:10.1016/s0010-2180(03)00058-0

Cited by 123 publications

(48 citation statements)

References 9 publications

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“…One thing should be noticed that this observed trend with regard to the stability response against the thermal conductivity seems to contradict to the well-known excess enthalpy combustion concept [e.g. [3][4][5][6][7][8][9][10][11]. There must be at least three reasons to explain; the first is to accumulate heat at the burner tip to increase the temperature to reduce the heat loss from the flame toward the burner, the second is to accumulate heat at the burner tip to enhance the reaction kernel formed at flame leading edge, and the third is to accumulate heat at the burner tip to enhance the potential chemical reaction inside the burner tube (as discussed in Sec.…”

Section: Fundamental Characteristics Of Microflames In Preheated Airmentioning

confidence: 88%

“…The channel wall plays a role of heat transfer medium for the heat recirculation in the case of the Swiss roll combustor. Recently, the fundamental characteristics of the premixed flame in a heated micro channel were studied in the context of this combustor [9][10][11], revealing that utilizing such heat recirculation is one of promising way in miniaturizing combustion devices. Interestingly, all existing combustors/burners utilizing the heat recirculation for further stabilization have been only considered in the premixed flame, although the same strategy could also be applied to the diffusion (i.e., non-premixed) flame.…”

Section: Stabilizing Technique For Small-scale Flamesmentioning

confidence: 99%

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Experimental study on the unique stability mechanism via miniaturization of jet diffusion flames (microflame) by utilizing preheated air system

Fujiwara

Nakamura

2013

Combustion and Flame

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In this work, we study the near-extinction behavior of micro-jet diffusion (i.e. non-premixed) flame, so called microflame, formed in a preheated air (up to 1020 K) in order to elucidate the unique and promising stability mechanism due to miniaturization of the jet diffusion flame. Effects of fuel flow rate and preheated air temperature on overall flame shape, flame temperature and the burner tip temperature are examined experimentally. Furthermore, the slight premixing effect on the near-extinction character is also investigated in order to support the stability mechanism suggested by this study. Methane is used as fuel and the several kinds of burner material are employed in order to examine the role of the burner. It turns out that the increasing the preheated air temperature decreases the limiting minimum flow rate effectively to simulate well the ideal condition of miniaturization of jet flame. This allows the flame to stay close to the burner and suppress the heat loss to the ambient, accordingly, the burner tip is substantially heated up. Then, the fuel flowing through the burner "receives" the heat from the burner (heated by flame) effectively to enhance the reactivity, resulting in improving the stability. It is also suggested that the endothermic radical-chain reactions are promoted 2 near the exit of the burner when the burner temperature is substantially heated, at which the back-diffused oxygen is penetrated. Our experimental observations convince the existence of the unique and promising stability mechanism apparently found in the miniaturization of the jet diffusion flame, where the flame and burner scale are almost identical and their thermal interaction becomes prominent.

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Section: Fundamental Characteristics Of Microflames In Preheated Airmentioning

confidence: 88%

Section: Stabilizing Technique For Small-scale Flamesmentioning

confidence: 99%

Experimental study on the unique stability mechanism via miniaturization of jet diffusion flames (microflame) by utilizing preheated air system

Fujiwara

Nakamura

2013

Combustion and Flame

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“…Available at www.ThermalFluidsCentral.org 2 geometry such as wall thickness (Hua et al, 2005), combustor diameter (axisymmetric models) or distance between two planar plates (2D models), heat transfer surface and inserting backward facing-step (Ju and Choi, 2003) play crucial roles in establishing a stable and efficient combustion in a micro-tube/channel. This phenomena may occur due to several reasons such as heat loss variations, heat transfer from post-flame to pre-flame zone (Hua et al, 2005;Leach and Cadou, 2005), the increment of reactive mixture residence time (Norton and Vlachos, 2003) and enhancement of mixing process, respectively.…”

Section: Frontiers In Heat and Mass Transfermentioning

confidence: 99%

“…Many experimental and numerical investigations which have been conducted are concentrated on the effects of some crucial options such as micro-tube/channel geometry Kim and Maruta, 2006;, heat loss (Hua et al, 2005;, thermal and radical quenching , fluid flow characteristic and equivalence ratio (Hua et al, 2005;Zhang et al, 2007), and pre-heating of fresh entrance reactive mixture (Hua et al, 2005;Ju and Choi, 2003;Leach and Cadou, 2005;Norton and Vlachos, 2003;Raimondeau et al, 2002) on combustion phenomena in micro-combustors. As results of many investigations, it can be inferred that the micro-combustor…”

Section: Introductionmentioning

confidence: 99%

Effect of Wall Thermal Conductivity on Hydrogen-Assisted Catalytic Ignition Characteristics of Propane-Air at Micro-Scales in Different Feeding Modes

Chen¹,

Gao²,

Xu³

2015

Frontiers in Heat and Mass Transfer

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Effect of wall thermal conductivity on hydrogen self-ignition and hydrogen-assisted ignition of propane-air mixtures in different feeding modes from ambient cold-start conditions were investigated numerically with chemical kinetic model in Pt/γ-Al2O3 catalytic micro-combustors. For the steady and transient state, effect of wall thermal conductivity on self-ignition characteristics of lean hydrogen-air mixtures was presented, and hydrogenassisted combustion of propane-air mixtures was investigated numerically in the co-feed mode and the sequential feed mode. The computational results indicate the large thermal inertia of the micro-combustor solid structure leads to slow temperature dynamics, and transient response is dominated by the thermal inertia. The heat localization in poorly conducting walls leads to fast ignition and shorter steady state time. In general, the concentration of hydrogen required for propane ignition increased with increasing wall thermal conductivity, decreasing inlet velocity, and decreasing inlet equivalence ratio of propane-air mixtures. In the co-feed mode, the combustion characteristics of hydrogen-assisted propane qualitatively resemble the selectively preheating initial portion of the combustion chamber wall. In the sequential feed mode, the time taken to reach steady state, the hydrogen cut-off time, the propane ignition time and the cumulative propane emissions increased with increasing wall thermal conductivity; the ignition characteristics are similar to partially preheating the initial segment for low and moderate wall thermal conductivity values (0.5 and 20 W/m· K); however, the ignition characteristics are close to completely heating the micro-combustor wall for high wall thermal conductivity values (200 W/m· K).

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“…In this type of burners, the burned gas heat is recycled to preheat the unburned mixture, reducing the effect of the heat losses through the walls. In order to understand the dynamics of a flame with heat recirculation, Ronney [17], Ju and Choi [18] and Sánchez-Sanz [19] carried out theoretical studies in simplified geometries demonstrating, in particular, the extension of the flammability limits to leaner flames and the reduction of the minimum burner size that allows combustion as a function of the amount of heat recirculated.…”

Section: Introductionmentioning

confidence: 99%

Effect of the equivalence ratio, Damköhler number, Lewis number and heat release on the stability of laminar premixed flames in microchannels

Sánchez–Sanz

Fernández-Galisteo

Kurdyumov

2014

Combustion and Flame

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This is a postprint version of the following published document:Sánchez-Sanz, M. ; Fernández-Galisteo, D. ; Kurdyumov, V. N. Effect of the equivalence ratio, Damköhler number, Lewis number and heat release on the stability of laminar premixed flames in microchannels. Combustion and Flame, 2014, 161 (5) The effect of the equivalence ratio on the stability and dynamics of a premixed flame in a planar microchannel with a step-wise wall temperature profile is numerically investigated using the thermo-diffusive approximation. To characterize the stability behavior of the flame, we construct the stability maps delineating the regions with different flame dynamics in the inlet mass flow rate m vs. the equivalence ratio / parametric space. The flame stability is analyzed for fuels with different diffusivity by changing the Lewis numbers in the range 0:3 6 Le F 6 1:4. On the other hand, the Lewis number of the oxidizer is kept constant and equal to unity Le O ¼ 1. Our results show that, for very diffusive fuels, the stability of the flame varies significantly with the equivalence ratio, transitioning from stable flames for lean mixtures to highly unstable flames when / > 1. As the fuel Lewis number approaches unity, the stability behavior of the flame for lean and rich mixtures becomes more similar to give, in the equidiffusional case Le F ¼ 1, a symmetric stability map around the stoichiometric mixture / ¼ 1. In all cases considered, the most stable flames are always found around the stoichiometric mixtures / ¼ 1, when the flame instabilities are completely suppressed for very diffusive fuels Le F < 1, or are reduced to a narrow range of inflow velocities for fuel Lewis numbers equal or greater than unity.The ratio between the size of the channel and the flame thickness d turns out to be of great importance in the stability behavior of the flame. Keeping the rest of parameters constant, an increase in d for lean flames makes the flame considerably more unstable, confirming the findings of previous works. Nevertheless, as the stoichiometric ratio approaches / ¼ 1, that trend is reversed to give flames that become more stable as the size of the channel is increased.

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An analysis of sub-limit flame dynamics using opposite propagating flames in mesoscale channels

Cited by 123 publications

References 9 publications

Experimental study on the unique stability mechanism via miniaturization of jet diffusion flames (microflame) by utilizing preheated air system

Experimental study on the unique stability mechanism via miniaturization of jet diffusion flames (microflame) by utilizing preheated air system

Effect of Wall Thermal Conductivity on Hydrogen-Assisted Catalytic Ignition Characteristics of Propane-Air at Micro-Scales in Different Feeding Modes

Effect of the equivalence ratio, Damköhler number, Lewis number and heat release on the stability of laminar premixed flames in microchannels

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