Abstract:The structure of stationary adiabatic premixed flames within porous inert media under intense interphase heat transfer is investigated using the asymptotic expansion method. For the pore sizes of interest for combustion in porous inert media, this condition is reached for extremely lean mixtures where lower flame velocities are found. The flame structure is analysed in three distinct regions. In the outer region (the solid-phase diffusion length scale), both phases are in local thermal equilibrium and the prob… Show more
“…Efficiency in foam with higher porosity is more than the lower one because a more complete combustion occurred in higher porosity foam. 21,40 Figure 12.Effect of porosity on efficiency.…”
An experimental setup was developed to investigate the physical characteristics of ceramic foam, used in reaction layer, on the performance of a porous burner. This premixed burner included mainly four sections: premixed, preheating, combustion zone and an integrated heat exchanger. The objective of this work was to investigate effects of different kinds of ceramic foams with various porosity, pore density and materials on the burner performance. The combustor was operated with natural gas and diverse structures of alumina and silicon carbide foam utilized in the reaction layer. Temperature distribution along the centerline, thermal efficiency, emission concentration and pressure drop were thoroughly investigated. Results showed a decrease in the porosity of ceramic foams, causing emission and pressure drop to increase while efficiency declined. More stable combustion was achieved by using finer foams with higher pore density. These foams indicated lower pollution and higher efficiency in low excess air, while coarser foams—ceramic foams with low pore density—resulted in lower pollution and higher efficiency in high excess air. Investigation effect of material exhibited silicon carbide foams causing higher temperature of the combustion and more temperature variation through the burner. Generally, material effect was negligible in terms of efficiency. But role of material highlighted in pollution where silicon carbide resulted in higher amount of NO.
“…Efficiency in foam with higher porosity is more than the lower one because a more complete combustion occurred in higher porosity foam. 21,40 Figure 12.Effect of porosity on efficiency.…”
An experimental setup was developed to investigate the physical characteristics of ceramic foam, used in reaction layer, on the performance of a porous burner. This premixed burner included mainly four sections: premixed, preheating, combustion zone and an integrated heat exchanger. The objective of this work was to investigate effects of different kinds of ceramic foams with various porosity, pore density and materials on the burner performance. The combustor was operated with natural gas and diverse structures of alumina and silicon carbide foam utilized in the reaction layer. Temperature distribution along the centerline, thermal efficiency, emission concentration and pressure drop were thoroughly investigated. Results showed a decrease in the porosity of ceramic foams, causing emission and pressure drop to increase while efficiency declined. More stable combustion was achieved by using finer foams with higher pore density. These foams indicated lower pollution and higher efficiency in low excess air, while coarser foams—ceramic foams with low pore density—resulted in lower pollution and higher efficiency in high excess air. Investigation effect of material exhibited silicon carbide foams causing higher temperature of the combustion and more temperature variation through the burner. Generally, material effect was negligible in terms of efficiency. But role of material highlighted in pollution where silicon carbide resulted in higher amount of NO.
“…There has been an extensive body of theoretical and experimental research on combustion using porous burners including the usage of catalysts, e.g. [28][29][30][31][32]. However, the controlling mechanisms still need to be better understood and the development of reliable models specifically for ultra-lean combustion in practical burners remains challenging.…”
Section: Overview Of Ultra-lean Methane Combustionmentioning
confidence: 99%
“…Heat is recovered via the thermal energy of the exhaust gases or radiant heating from the porous solid [27][28][29][30][31][32] The stability of the oxidation/combustion process to fluctuations in fuel concentration and flow rate, the development of reliable models for ultra-lean combustion, as well as optimising burner performance for lean-burn applications TFRR Recuperative combustion using flow reversal to transfer the heat of combustion to the incoming air via a solid heat storage medium [15] Similar to those for porous burners, with design optimisation of the regenerative beds for heat recuperation CFRR In the context of low concentration CH 4 oxidation/combustion, the concept of moderate or intense low-oxygen dilution (MILD) combustion [37] is relevant. The interest in MILD combustion has been mainly driven by the needs for low emission and high efficiency combustion.…”
ABSTRACT:Anthropogenic emissions of non-CO 2 greenhouse gases such as fugitive methane contribute significantly to global warming. A review of fugitive methane combustion mitigation and utilisation technologies, which are primarily aimed at methane emissions from coal mining activities, with a focus on modelling and simulation of ultra-lean methane oxidation/combustion is presented. The challenges associated with ultra-lean methane oxidation are on the ignition of the ultra-lean mixture and sustainability of the combustion process. There is a lack of fundamental studies on chemical kinetics of ultra-lean methane combustion and reliable kinetic schemes that can be used together with computational fluid dynamics studies to design and develop advanced mitigation systems. Mitigation of methane as a greenhouse gas calls for more efforts on understanding ultra-lean combustion. Recuperative combustion provides a promising means for mitigating ultra-lean methane emissions. Progress is needed on effective methods to ignite and to recuperate and retain heat for oxidation/combustion of the ultra-lean mixtures. Catalysts can be very effective in reducing the temperatures required for oxidation while plasmas may be utilised to assist the ignition, but thermodynamic/aerodynamic limits of burning ultra-lean methane remain unexplored. Further technological developments may be focussed on developing innovative capturing technology as well as technological innovations to achieve effective ignition and sustainable oxidation/combustion.
“…Excess enthalpy combustion in porous media [1,2], also known as energy concentration, draws constant interest from researchers due to its wide range of applications and outstanding features of heat recovery and pollutant control. The energy concentration phenomenon and combustion characteristics in porous burners have been investigated extensively in the literature including experimental [3][4][5][6][7][8], numerical [9][10][11][12][13][14][15][16] and analytical studies [16][17][18][19][20][21][22][23][24][25][26][27]. Babkin et al [21] presented a detailed review of this issue and stated that the phenomenon of energy concentration is more widespread in nature than was assumed previously.…”
Section: Introductionmentioning
confidence: 99%
“…Pereira's research group [22][23][24][25] carried out a series of studies on laminar stationary premixed flames within porous inert media. Their analysis was based on the excess enthalpy function applied to a set of one-dimensional volume-averaged equations.…”
The superadiabatic combustion for non-stationary filtration combustion is analytically studied. The non-dimensional excess enthalpy function (
H
) equation is theoretically derived based on a one-dimensional, two-temperature model. In contrast to the
H
equation for the stationary filtration combustion, a new term, which takes into account the effect of non-dimensional combustion wave speed, is included in the
H
equation for transient filtration combustion. The governing equations with boundary conditions are solved by commercial software Fluent. The predictions show that the maximum non-dimensional gas and solid temperatures in the flame zone are greater than 3 for equivalence ratio of 0.15. An examination of the four source terms in the
H
equation indicates that the thermal conductivity ratio
(
Γ
s
)
between the solid and gas phases is the dominant one among the four terms and basically determines
H
distribution. For lean premixed combustion in porous media, the superadiabatic combustion effect is more pronounced for the lower
Γ
s
.
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