燃烧在多孔介质中的研究

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"Combustion in Porous Media" 是一篇由 M.M. Kamal 和 A.A. Mohamad 合著的论文，发表在《机械工程师学会会刊：动力与能源部分》(Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy) 2006 年第 220 卷第 5 期，文章编号为 JPE169。在线版本可以在 DOI: 10.1243/09576509JPE169 查找到。这篇文章深入探讨了多孔介质中的燃烧（Combustion in Porous Media）这一主题，这是能源工程领域的一个重要话题。多孔介质通常指的是具有大量孔隙和微小通道的材料，如陶瓷、泡沫金属或某些类型的岩石。在这些介质中发生的燃烧过程涉及到复杂的热传递、化学反应和流体动力学相互作用。燃烧在多孔介质中的研究具有广泛的应用背景，包括燃料电池、热电转换、能源储存和环境工程。例如，多孔介质燃烧可以用于提高燃料效率，减少污染物排放，以及在热管理和能源转换系统中的应用。作者可能讨论了以下关键知识点： 1. **多孔介质的特性**：多孔材料的孔隙结构对燃烧过程有着显著影响，包括孔隙大小、形状、连通性和热容等。 2. **燃烧模型**：文章可能涉及了描述多孔介质内燃烧的数学模型，这些模型可能基于连续介质假设或离散网络模型，并考虑了化学反应动力学、扩散和对流效应。 3. **传热和传质**：燃烧过程中，热量和燃料分子在多孔介质内的传输是关键。作者可能讨论了固-气、固-液界面的传热以及气体在孔隙中的扩散现象。 4. **稳定性分析**：燃烧前沿的稳定性是多孔介质燃烧研究的重要方面，可能涉及到稳态燃烧、自燃和熄火条件的探讨。 5. **实验方法与设备**：为了验证理论模型，作者可能会介绍一些实验技术，如光学成像、热释电传感器和激光诊断等。 6. **应用实例**：论文可能会展示一些实际应用案例，如多孔介质燃烧在固体氧化物燃料电池（SOFC）中的应用，以及在新型燃烧器设计中的创新。 7. **环境与经济影响**：燃烧效率的提高和污染物排放的减少对于环境保护和经济效益有显著影响，可能也会在文中提及。 "Combustion in Porous Media" 这篇论文对多孔介质燃烧的理论和实践进行了详尽的研究，对理解这一复杂过程及其潜在应用具有重要价值。

proﬁles exhibit a maximum at the exit side of the

ﬂow. Thereafter, the ﬂow direction is altered to the

opposite side by the aid of four valves (Fig. 3). On

the reverse ﬂow half-cycle, the fresh combustibles

are encountering much higher solid temperatures

at the entering side (which was highly heated by

the combustion products on the previous half-

cycle). Consequently, the amount of heat recycled

becomes larger than that with the single ﬂow direc-

tion and hence the degree of excess enthalpy is

higher. In such a case, after combustion releases

the energy, the gas temperatures on the reverse

half-cycle will continue to rise towards the exit side

(which was the entrance side in the previous half-

cycle) and the temperature maximum region will

be shifted towards that exit side with a subsequent

broadening in the solid heated length. When the per-

iodic time for the ﬂow switch is properly adjusted

and a steady-state condition is reached, the tempera-

ture proﬁles will exhibit a trapezoidal shape (Fig. 4).

This mechanism cannot be produced by single ﬂow

direction, as the direction of solid heat transfer is

from higher to lower solid temperatures, which

then settles a single gradient for both sol id and gas

temperature proﬁles. Conversely, in the reciprocat-

ing ﬂow system, the heat transfer from the combus-

tion gases raises the solid temperatures from both

directions. This consequently leads to the trapezoi-

dal shape and the higher temperature rise from

both sides with a net gas temperature increase at

the exit (Fig. 4). At the optimum ﬂow reversal peri-

odic time, the maximum temperature rise in the

porous medium excee ded the theoretical one by a

factor of about 2.2. Extinction occurred by lowering

the heat transfer coefﬁcient, the thermal conduc-

tivity, or the heat capacity of the solid relative to

the gas. Hoffmann et al. [38] analysed the develop-

ment of temperature proﬁles in the porous solid

during a half-cycle. By increasing the half-cycle

time, the temperature proﬁle turned to a triangular

shape and a further increase led to ﬂame extinction.

3.3 Utilization of porous burners for synthetic gas

production

Similar to the extension in the lean operation equiv-

alence ratio for combustion in porous media by the

preheating effect, there is also an extension in the

upper ﬂammability limit for rich gaseous mixtures.

This feature is utilized for production of syngas

(CO þ H

) by burning hydrocarbon fuels in a

deﬁcient supply of air, so that the following partial

oxidation may take place

þ mO

! 2mCO þ nH

(1)

Because the rates of elementary reactions leading

to the above overall reaction are low at the adiabatic

ﬂame temperatures of rich mixtures (below 1000 8C),

the insertion of porous media provides the internal

heat recirculation necessary to sustain the partial

oxidation. Therefore, super-adiabatic temperatures

are obtained and reactions are drive n to produce

and CO. The necessity in compact and efﬁcient

hydrogen source for fuel-cell-powered vehicles

stimulates studies to develop technologies for

reforming hydrocarbon fuels. For such development,

numerous works have been performed to investigate

the rich gas mixture combustion in porous burners.

The major parameters that affect reaction rates in

these burners were found to be the maximum tempe-

rature and residence time, as reported by Bingue

et al. [39], Drayton et al. [40], and Kennedy et al.

[41]. In the work of Pedersen-Mjaanes et al. [42], a

stationary ﬂame could be stabilized in an insulated

porous burner. The hydrogen production was

Fig. 4 Steady-state gas temperature proﬁle for a half-

cycle inside reciprocating ﬂow porous

medium burner [35]

Fig. 3 Reciprocating ﬂow in a porous medium burner

490 M M Kamal and A A Mohamad

Proc. IMechE Vol. 220 Part A: J. Power and Energy JPE169

IMechE 2006

at University of Victoria on August 30, 2012pia.sagepub.comDownloaded from

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