Superadiabatic combustion in a porous medium

Hanamura, Katsunori; Echigo, Ryozo; Жданок, С. А.

doi:10.1016/0017-9310(93)90004-p

Cited by 144 publications

(46 citation statements)

References 6 publications

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“…(11)- (14) On the other hand, the mass recirculation, together with the heat recirculation, is used in the high-temperature air combustion. It was reported that unique combustion phenomena are observed under the conditions that the temperature of mixtures is sufficiently high and the oxygen concentration in mixtures is considerably low.…”

Section: Introductionmentioning

confidence: 99%

Asymptotic Analysis on High-temperature Premixed Flames: Instability of Flame Fronts under the Constant-enthalpy Conditions

Kadowaki

2010

JTST

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Asymptotic analysis on premixed flames with high-temperature combustible mixtures was performed to elucidate the instability of flame fronts. Planar premixed flames with sufficiently low Mach numbers were treated, and a one-step irreversible chemical reaction with sufficiently high activation energy was assumed. Through the asymptotic analysis, we obtained the formula for the burning velocity, depending on the temperature of burned and unburned gases and on the mass fraction of fuel. To investigate the instability of high-temperature premixed flames under the constant-enthalpy conditions, we obtained the instability intensity which depended on the burning velocity and on the temperature ratio of burned and unburned gases, where the burned-gas temperature was constant. As the unburned-gas temperature became higher, the instability intensity became higher, except for premixed flames with low reaction exponents under the conditions of constant-density unburned gases. This was because that the instability intensity was determined by the competition between the increase of the burning velocity and the decrease of the temperature ratio.

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Section: Introductionmentioning

confidence: 99%

Asymptotic Analysis on High-temperature Premixed Flames: Instability of Flame Fronts under the Constant-enthalpy Conditions

Kadowaki

2010

JTST

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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: 87%

“…This stabilization mechanism should exist when the strong thermal interaction between the flame and the burner by the militarization is introduced. After all, we can conclude that such heat recirculation through the burner is one of unique feature of flame stabilization for miniaturizing jet diffusion flames, based on something similar concept of excess enthalpy combustion (normally using premixed flame, not reported ever diffusion flame) [3][4]8]. > 820 K) …”

Section: Role Of Burner As Heat Recirculation Mediummentioning

confidence: 94%

“…One example is a Swiss-roll combustor that consists of two spiral channels with combustion space at the center [3][4][5]. Its fundamental concept is based on excess enthalpy combustion proposed by Weinberg [6] which also have been applied to the porous burner to attain the low-load combustion [7,8]; namely, recirculate the combustion-generated heat toward the unburned premixed gas in pre-burning process. The channel wall plays a role of heat transfer medium for the heat recirculation in the case of the Swiss roll combustor.…”

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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“…2,3) In the proposed system, a dilute fuel gas is introduced alternately from both sides of the porous element, and trapezoidal temperature profiles with maximum temperatures high enough to sustain combustion are kept inside the element. 4,5) The trapezoidal temperature distribution is particularly favorable for thermoelectric power generation, thus the porous element could effectively produce electricity under such a large temperature gradient. Cho and co-workers developed a porous chromel and almel sintered elements having the porosity ratio of about 30%.…”

Section: Introductionmentioning

confidence: 99%

Temperature Distributions and Thermoelectrical Performance of a Porous FeSi<SUB>2</SUB> Element in a Steady State of Reciprocatory Flow Combustion

Katsuki¹,

Tomida²,

Nakatani³

et al. 2002

Mater. Trans.

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Temperature distributions and thermoelectrical performance of a porous FeSi 2 in a steady state of reciprocatory flow combustion have been examined. The temperature gradient between the hot and the cold side of the elements reached about 200 K/cm, resulting in high output power per density of 226 Wh/m 2 . It has been also found that the incoming gases were preheated by the porous element to a temperature where combustion occurs and exhaust gases transferred the thermal energy to the element before leaving the element. This energy recirculation leads to an extension of the flammable limit for dilute fuel gases, equivalence ratio; φ = 0.27. The low conversion efficiency of 0.033% would be attributed to the convective heat loss by the exhaust gases due to the small volumetric surface area inside the porous element.

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Superadiabatic combustion in a porous medium

Cited by 144 publications

References 6 publications

Asymptotic Analysis on High-temperature Premixed Flames: Instability of Flame Fronts under the Constant-enthalpy Conditions

Asymptotic Analysis on High-temperature Premixed Flames: Instability of Flame Fronts under the Constant-enthalpy Conditions

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

Temperature Distributions and Thermoelectrical Performance of a Porous FeSi<SUB>2</SUB> Element in a Steady State of Reciprocatory Flow Combustion

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