甲烷/空气混合物在微小型钝体燃烧器中的燃烧特性

为了实现在淬熄距离以下的稳定燃烧,试验设计了两种带钝体的回热型燃烧器,研究预混甲烷在高度小于淬熄距离的燃烧室中的燃烧特性。燃烧器的燃烧室高度为2 mm,长度为20 mm,进口处安装了边长为1mm的等边三角形钝体或相同尺寸的"V"形钝体,并在上下两侧设置了预热通道。利用Fluent6.3软件对甲烷/空气在这两个燃烧器的预混燃烧做了数值模拟,确定了浓度极限和速度极限,并对稳燃机理进行了分析。与三角形钝体燃烧器相比较,"V"形钝体燃烧器的稳燃范围更大。在所给出的稳定燃烧工况下两者的燃烧效率均在99%以上,甲烷/空气的混合气体能够完全燃烧。但当进气速度较小同时当量比较大时会发生回火现象。     

Combustion of methane in catalytic honeycomb monolith burners

The heat transfer efficiency, stability, and pollutant emissions characteristics of ultra‐lean methane–air combustion in some precious metal‐based honeycomb monoliths were investigated. The interpretation of the experimental results was assisted using numerical modelling of the gas‐phase combustion process. The thermal radiation output of the monoliths varied between 27 and 30 per cent of the thermal input, and this compared favourably with equivalent porous inert media burners. The minimum fuel concentrations for very‐low emission stable combustion were found to be significantly lower than for conventional gas‐phase combustion and were shown to vary with the nature and loading of the catalyst, as well as with flow rates. The palladium catalyst was found to have a larger window of mixture strengths and flow rates for stable operation than the platinum one. During all the runs under stable combustion conditions, only extremely small amounts of CO, NO_x and unburnt hydrocarbons were detected. Thus, the operating conditions verified ‘near‐zero’ pollutant emissions that only a catalytic combustion process can achieve at present. Temperature profiles inside the monoliths channels proved that the catalyst's role was not only to enable the ignition of fuel mixtures below flammability limits, but also to ensure the complete oxidation of the fuel to CO₂ via surface reactions in the steady state. The reaction zone inside the catalysts was found to end at about 10 mm from the monolith's entrance. The effect of monolith length was investigated and a reduction of 70 per cent in the original length was found possible. Copyright © 2000 John Wiley & Sons, Ltd.     

Gas phase chemistry in catalytic combustion of methane/air mixtures over platinum at pressures of 1 to 16 bar

The gas-phase combustion of fuel-lean methane/air premixtures over platinum was investigated experimentally and numerically in a laminar channel-flow catalytic reactor at pressures 1 bar?p?16 bar. In situ, spatially resolved one-dimensional Raman and planar laser induced fluorescence (LIF) measurements over the catalyst boundary layer were used to assess the concentrations of major species and of the OH radical, respectively. Comparisons between measured and predicted homogeneous (gaseous) ignition distances have led to the assessment of the validity of various elementary gas-phase reaction mechanisms. At low temperatures (900 K?T?1400 K) and fuel-to-air equivalence ratios (0.05?φ?0.50) typical to catalytic combustion systems, there were substantial differences in the performance of the gaseous reaction mechanisms originating from the relative contribution of the low- and the high-temperature oxidation routes of methane. Sensitivity analysis has identified the significance of the chain-branching reaction CHO + M = CO + H + M on homogeneous ignition, particularly at lower pressures. It was additionally shown that C2 chemistry could not be neglected even at the very fuel-lean conditions pertinent to catalytic combustion systems. A gas-phase reaction mechanism validated at 6 bar?p?16 bar has been extended to 1 bar?p?16 bar, thus encompassing all catalytic combustion applications. A reduced gas-phase mechanism was further derived, which when used in conjunction with a reduced heterogeneous (catalytic) scheme reproduced the key catalytic and gaseous combustion characteristics of the full hetero/homogeneous reaction schemes.     

Numerical investigation of premixed hydrogen/air combustion at lean to ultra-lean conditions and catalytic approach to enhance stability

Premixed combustion of hydrogen/air over a platinum (Pt) catalyst is numerically investigated in a planar channel burner with the aim of stabilising the flame at lean to ultra-lean conditions. A steady laminar species transport model is examined in conjunction with elementary heterogeneous and homogeneous chemical reaction schemes and validated against experimental results. A stability map is obtained in a non-catalytic burner for the equivalence ratios (φ) of 0.15–0.20, which serves as the basis for the catalytic flame analysis. Over the Reynolds numbers (Re) investigated in the non-catalytic burner, no flame is observed for φ ≤ 0.16, and flame extinction occurs at Re < 571 and Re < 381 for φ = 0.18 and 0.20, respectively. Moreover, a significant amount of unburned H₂ exits the burner in all cases. With the Pt catalyst coated on the walls, complete H₂ combustion is attained for 0.10 ≤ φ ≤ 0.20 where the contribution of gas phase (homogeneous) reaction increases with Re. Furthermore, radiation on the wall and at the inlet affects the combustion kinetics and flame temperature. Finally, NO_x emission is investigated under the same conditions and found to increase with equivalence ratio but has a negligible effect with the inflow Reynolds number.     

Numerical study of the physical and chemical effects of hydrogen addition on laminar premixed combustion characteristics of methane and ethane

Methane and ethane are taken as the research objects. Using H₂ as diluent, based on Chemkin II/Premix Code and modified detailed chemical reaction mechanism: GRI 3.0*-Mech (introducing three hypothetical substances of FH₂, FO₂ and FN₂), the physical and chemical effects of hydrogen on laminar burning velocities (LBVs), adiabatic flame temperatures (AFTs), net heat release rates (NHRRs) and elementary reactions responsible for temperature changes of two alkanes under different equivalence ratios were analyzed and determined. Results showed that the chemical effect of H₂ promotes the LBVs and ATFs of methane and ethane, while the physical effect decreases the two parameters. In addition, the physical effects of H₂ inhibit the chemical reactions of methane and ethane, resulting in the decrease of NHRRs. The chemical effect of H₂ accelerates the process of chemical reaction and obviously increases the NHRRs. The two most vital elementary reactions that promote the temperature rise of methane and ethane are H + O₂ <=> OH + O and CO + OH <=> H + CO₂. The important reactions responsible for inhibiting the temperature rise are H + CH₃(+M) <=> CH₄(+M) and H + O₂ + H₂O <=> HO₂ + H₂O.     

Enhancement of heat recirculation on the hysteresis effect of catalytic partial oxidation of methane

The hysteresis characteristics of catalytic partial oxidation of methane (CPOM) in a Swiss-roll reactor are predicted numerically by varying Damköhler number. Particular attention is paid to the influences of heat recirculation, gas hourly space velocity (GHSV), and atomic O/C ratio on the hysteresis loop and performance of CPOM. The reactions of methane combustion, steam reforming, and CO₂ or dry reforming are simultaneously considered. The results reveal that preheating reactants through excess enthalpy recovery is conducive to the ignition of CPOM and extending its extinction limit, so the ignition and extinction Damköhler numbers are lowered. The analysis also suggests that steam reforming is more sensitive to the heat recovery than methane combustion and dry reforming. An increase in GHSV reduces the residence time of reactants in the catalyst bed, thereby enlarging the ignition and extinction Damköhler numbers of CPOM. A higher O/C ratio facilitates the ignition of CPOM, stemming from more oxygen supplied, but the ratio should be controlled below 1.2. From the hysteresis phenomena, hydrogen can be produced from methane at a lower Damköhler number to save more energy for performing CPOM.     

Impinging premixed butane/air circular laminar flame jet--influence of impingement plate on heat transfer characteristics

Experimental studies were performed to study the heat transfer characteristics of an impingement flame jet system consisting of a premixed butane/air circular flame jet impinging vertically upward upon a horizontal rectangular plate at laminar flow condition. There were two impingement plates manufactured with brass and stainless steel respectively used in the present study. The integrated effects of Reynolds number and equivalence ratio of the air/fuel jet, and distance between the nozzle and the plate (i.e. nozzle-to-plate distance) on heat transfer characteristics of the flame jet system had been investigated. The influence in using impingement plate with different thermal conductivities, surface emissivities and roughnesses on heat flux received by the plate was examined via comparison, which had not been reported in previous literatures. A higher resistance to heat transfer had been encountered when the stainless steel impingement plate of lower thermal conductivity was used, which led to a significantly lower heat flux at the stagnation region. However, the heat flux distribution in the wall-jet region of the plate was only slightly affected by using different impingement plates. Because of the significantly lower heat transfer, more fuel was not required to consume and existed at the stagnation region of the stainless steel impingement plate, which would be burned latter in the wall-jet region to release its chemical energy and enhance the local heat flux there.     

Combustion characteristics and radiation performance of premixed hydrogen/air combustion in a mesoscale divergent porous media combustor

To improve flammability and radiation efficiency, a divergent porous media combustor is proposed and numerically studied. The local thermal non-equilibrium model is used to consider the temperature difference between gas and solid matrix. Effects of equivalence ratio, the wall thermal conductivity, solid matrix thermal conductivity, and divergent ratio on combustion characteristics, radiation efficiency, and flammability limits are studied. The results show that the divergent channel extends the blowout limit by 186% and obtains a maximum radiation efficiency of 29.3%, increased by 70% compared with the straight channel. A smaller wall thermal conductivity is recommended considering the flammability range and radiation efficiency. A careful choice of solid matrix thermal conductivity and the divergent ratio is suggested to balance their opposing effects on the radiation efficiency and the flammability.     

Investigation of turbulent premixed methane/air and hydrogen-enriched methane/air flames in a laboratory-scale gas turbine model combustor

Methane and hydrogen-enriched (25 vol% and 50 vol% H₂-enriched CH₄) methane/air premixed flames were investigated in a gas turbine model combustor under atmospheric conditions. The flame operability ranges were mapped at different Reynold numbers (Re), showing the dependence on Re and H₂ concentrations. The effects of equivalence ratio (Φ), Re, and H₂ enrichment on flame structure were examined employing OH-PLIF measurement. For CH₄/air cases, the flame was stabilized with an M shape; while for H₂-enriched cases, the flame transitions to a П shape above a specific Φ. This transition was observed to influence significantly the flashback limits. The flame shape transition is most likely a result of H₂ enrichment, occurring due to the increase in flame speed, higher resistance of the flame to the strain rate, and change in the inner recirculation zone. Flow fields of CH₄/air flames were compared between low and high Re cases employing high-speed PIV. The flashback events, led by two mechanisms (combustion-induced vortex breakdown, CIVB, and boundary-layer flashback, BLF), were observed and recorded using high-speed OH chemiluminescence imaging. It was found that the CIVB flashback occurred only for CH₄ flames with M shape, whereas the BLF occurs for all H₂-enriched flames with П shape.     

Experimental study on the propagation characteristics of hydrogen/methane/air premixed flames in a narrow channel

This work is focused on the explosion characteristics of premixed gas containing different volume fractions of hydrogen in a narrow channel (1000 mm × 50 mm × 10 mm) under the circumstance of stoichiometric ratio. The ignition positions were set in the closed end and the middle of the pipeline respectively. The results showed that when the gas was ignited at the pipeline closed end, the propagating flame was tulip structure for different premixed gas. When the hydrogen volume fraction was less than 40%, the flame propagation speed increased significantly with the rise of hydrogen volume fraction, and the overpressure peak also appeared obviously in advance. However, when the volume fraction of hydrogen was more than 40%, the increase of flame propagation speed and the overpressure peak occurrence time varied slightly. Furthermore, when the ignition position was placed in the middle of the pipeline, the flame propagation speed propagating to the opening end was much faster than that propagating to the closing end, and there was no tulip shape when the flame propagates to the opening end. The flame propagating to the closed end appeared tulip shape under the influence of airflow, and high-frequency flame oscillation occurred during the propagation. This work shows that the hydrogen volume fraction and ignition position significantly affected the flame structure, flame front speed, and explosion overpressure.     

Effect of heat recirculation on the self-sustained catalytic combustion of propane/air mixtures in a quartz reactor

The self-sustained catalytic combustion of propane is experimentally studied in a two-pass, quartz heat-recirculation reactor (HRR) and compared to that in a no (heat) recirculation reactor (NRR). Structured monolithic reactors with Pt/γ-Al₂O₃, LaMnO₃/γ-Al₂O₃, and Pt doped perovskite catalysts have been compared in the HRR and NRR configurations. Heat recirculation enhances combustion stability, by widening the operating window of self-sustained operation, and changes the mode of stability loss from blowout to extinction. It is found that thermal shields (upstream and downstream of the monolith) play no role in the stability of a HRR but increase the stability of a NRR. The stability of a HRR follows this trend: Pt/γ-Al₂O₃ > doped perovskite > LaMnO₃/γ-Al₂O₃. Finally, a higher cell density monolith enlarges the operating window of self-sustained combustion, and allows further increase of the power density of the process.     

Non‐gray modeling of radiative heat transfer in hydrogen combustion scenarios

New weighted‐sum‐of‐gray‐gases model (WSGGM) parameters for H₂O vapor are derived from emissivity correlations in the open literature and presented for use in hydrogen combustion simulations. Predictions employing the new WSGGM are seen to compare favorably against the spectral‐line‐based WSGGM on benchmark problems as well as in media conditions representative of turbulent hydrogen diffusion flames (Sandia Flame A and a model hydrogen gas‐turbine combustor). The Sandia Flame A calculations were performed in a decoupled manner employing experimental measurements of temperature and gas compositions as inputs. The measured temperature variance data were employed to model the turbulence–radiation interactions. A coupled computational fluid dynamic (CFD) calculation was performed to obtain the conditions within the gas‐turbine combustor geometry. The observed accuracies of the proposed set of WSGGM parameters in conditions encompassing a wide range of H₂O vapor concentrations and temperature non‐homogeneities encountered in combustion media make them amenable to implementation in CFD codes. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental analysis of the effects of porous wall on flame stability and temperature distribution in a premixed natural gas/air combustion

In the present analysis, the flame stabilization and temperature distribution within a premixed burner contain porous wall are studied experimentally. The effects of inner diameter, length, and pore density of the porous wall, thermal load, equivalence ratio, and the inlet velocity of the fuel‐air mixture on these are studied. The fuel used in this study is natural gas and the porous wall is SiC (silicon carbide) ceramic foam. The experimental results clearly indicate that the axial temperature along the porous wall increases when the inner diameter of the porous wall decreases and its length increases. The porous wall temperature with an inner diameter of 40 mm, length of 66 mm, and pore density of 30 PPI (pores per inch) has the highest temperature among the examined states. The results of studying the effect of the porous wall on flame stability show that the flame stability limit has a direct relationship with the length and pore density of porous wall and an inverse relationship with the inner diameter of the porous wall. Also, it is found that the porous wall has the highest temperature causes the maximum flame stability limit.     

Numerical investigation on combustion characteristics of premixed hydrogen/air in a swirl micro combustor with twisted vanes

The combustion characteristics of the swirl micro combustor with twisted vanes (Swirl-MC-TV) and the conventional micro combustor (Conventional-MC) are investigated and compared under different inlet velocities (8–40 m/s), wall materials (quartz, steel, and SiC), and equivalence ratios (0.6–1.4). The results show that the larger area of recirculation zones and the stronger recirculation intensity are the key factors for Swirl-MC-TV to stable combustion. When the inlet velocity is 40 m/s, compared with the Conventional-MC, the wall heat loss of the Swirl-MC-TV is reduced by 15.9%, and the reaction heat and combustion efficiency of the Swirl-MC-TV are increased by 17.5% and 5.9%, respectively. When the wall materials of steel and SiC, combustors have a better preheating effect and higher combustion intensity. When the equivalence ratio is greater than 0.6, the wall heat loss of Swirl-MC-TV is larger but the combustion efficiency and the reaction intensity are still higher than Conventional-MC.     

Nonoxidative methane activation,coupling, and conversion to ethane,ethylene, and hydrogen over Fe/HZSM‐5, Mo/HZSM‐5, and Fe–Mo/HZSM‐5 catalysts in packed bed reactor

A high abundance of methane and its relatively low price make it an attractive raw feedstock for the production of ethylene, which is in the consumer demand in recent years. Direct catalytic nonoxidative conversion is interesting, because it could be utilized on natural gas well sites. Monometallic and bimetallic Fe and Mo catalysts were prepared for the purpose of the coupling to ethane and ethene. Three supported materials were synthesized with the following loading of metal: 2.5‐wt% Fe, 5.0‐wt% Fe, and 2.5‐wt% Mo on HZSM‐5. Process' chemical reactions were also catalyzed with a constant 2.5‐wt% Mo/HZSM‐5, which had different amounts of Fe, namely, 0.5, 1.0, and 2.5 wt%. Fourier transform infrared (FTIR), N₂ adsorption/desorption, NH₃ temperature‐programmed desorption (TPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) were applied for characterization. Coke, accumulated on spent solids, was determined by thermogravimetric analysis (TGA). Activity was evaluated in quartz‐packed bed reactor. All surfaces suffered from deactivation due to carbon formation. The addition of Fe to Mo increased CH₄ reacted. The highest selectivity for alkenes was achieved over 1.0‐wt% Fe to 2.5‐wt% Mo/HZSM‐5. At the peak of performance, the C‐based reactivity was 52% for olefins and 2% for alkanes. Stability was accomplished over 2.5‐wt% Fe/HZSM‐5, where the rate of C₂ synthesis was comparatively stable for 20 hours of the time on stream. The selective C‐basis yield for C₂H₄ and C₂H₆ was 36% and 23%, respectively. The lowest measured quantity of (carbonaceous) by‐products was deposited on 2.5‐wt% Fe/HZSM‐5 after 26 hours. Propylene was detected very limitedly.     

Numerical study on premixed hydrogen/air combustion characteristics and heat transfer enhancement of micro-combustor embedded with pin fins

Aimed at improving the energy output performance of the Microthermal Photovoltaic (MTPV) system, it is necessary to optimize the structure of the micro combustor. In this paper, micro combustor with in-line pin fins arrays (MCIPF) and micro combustor with both end-line pin fins arrays (MCEPF) were presented to realize the efficient combustion and heat transfer enhancement, and the influence of inlet velocity, equivalent ratio, and materials on thermal performance was investigated. The results showed that pin fins embedding is beneficial to improving combustion, and the combustion efficiency of MCIPF and MCEPF reaches 98.5% and 98.7%, which is significantly higher than that of the conventional cylindrical combustor (MCC). However, with the increase of inlet velocity from 8 m/s to 14 m/s, MCIPF exhibits the highest external wall temperature with a range of (1302–1386 K), while MCEPF maintains the best temperature uniformity. As the inlet velocity increases to 10 m/s, the external wall temperature and temperature uniformity reach the optimum. Besides, under the conditions of different equivalence ratios, both external wall temperature and heat flux increases first and then decreases, meanwhile the temperature uniformity of MCEPF is significantly improved compared with that of MCIPF, they all exhibit the highest external wall temperature with an equivalence ratio of 1.1, and the thermal performance is greatly enhanced. By comparing the heat transfer performance of combustors with different materials based on MCEPF, it is interesting to find that the application of high thermal conductivity materials can not only increase the external wall temperature, but also improve the temperature uniformity. Therefore, materials with high thermal conductivity such as Aluminum, Red Copper and Silicon Carbide should be selected for application in micro combustors and their components. The current work provides a new design method for the enhanced heat transfer of the micro combustor.     

Numerical investigation of hydrogen production via autothermal reforming of steam and methane over Ni/Al2O3 and Pt/Al2O3 patterned catalytic layers

In this study a numerical analysis of hydrogen production via an autothermal reforming reactor is presented. The endothermic reaction of steam methane reforming and the exothermic combustion of methane were activated with patterned Ni/Al₂O₃ catalytic layer and patterned Pt/Al₂O₃ catalytic layer, respectively. Aiming to achieve a more compacted process, a novel design of a reactor was proposed in which the reforming and the combustion catalysts were modeled as patterned thin layers. This configuration is analyzed and compared with two configurations. In the first configuration, the catalysts are modeled as continuous thin layers in parallel, while, in the second configuration the catalysts are modeled as continuous thin layers in series (conventional catalytic autothermal reactor). The results show that the pattern of the catalyst layers improves slightly the hydrogen yield, i.e. 3.6%. Furthermore, for the same concentration of hydrogen produced, the activated zone length can be decreased by 38% and 15% compared to the conventional catalytic autothermal reforming and the configuration where the catalysts are fitted in parallel, respectively. Besides, the oxygen consumption is lowered by 5%. The decrement of the catalyst amount and the oxygen feedstock in the novel studied design lead to lower costs and compact process.     

Effects of H2 or CO2 addition, equivalence ratio, and turbulent straining on turbulent burning velocities for lean premixed methane combustion

Using hydrogen or carbon dioxide as an additive, we investigate the bending effect of turbulent burning velocities (ST/SL) over a wide range of turbulent intensities (u^′/SL) up to 40 for lean premixed methane combustion at various equivalence ratios (?), where SL is the laminar burning velocity. Experiments are carried out in a cruciform burner, in which a sizable downward-propagating premixed CH₄/diluent/air flame interacts with intense isotropic turbulence in the central region without influences of ignition and unwanted turbulence from walls. Simultaneous measurements using the pressure transducer and pairs of ion-probe sensors at various positions of the burner show that effects of gas velocities and pressure rise due to turbulent combustion on ST of lean CH₄/H₂/air flames can be neglected, confirming the accuracy of the ST data. Results with increasing hydrogen additions (δ=10, 20, and 30% in volume) show that the bending of ST/SL vs u^′/SL plots is diminished when compared to data with δ=0, revealing that high reactivity and diffusivity of hydrogen additives help the reaction zone remaining thin even at high u^′/SL. In contrast, the bending effect is strongly promoted when CO₂ is added due to radiation heat losses. This leads to lower values of ST/SL at fixed u^′/SL and ?, where the slope n can change signs from positive to negative at sufficiently large u^′/SL, suggesting that the reaction zone is no longer thin. All ST data with various δ can be well approximated by a general correlation (ST−SL)/u^′=0.17Da^0.43, covering both corrugated flamelet and distributed regimes with very small data scatter, where Da is the turbulent Damköhler number. These results are useful in better understanding how turbulence and diluents can influence the canonical structures of turbulent premixed flames and thus turbulent burning rates.     

Roles of the state-resolved OH(A) and OH(X) radicals in microwave plasma assisted combustion of premixed methane/air: An exploratory study

We report a novel microwave plasma-assisted combustion (PAC) system that is developed as a new test platform to study roles of plasma in PAC. The system included two major components, an atmospheric pressure microwave plasma cavity and a cross-shape quartz combustor. This new PAC system allows one to study PAC using complicated yet well-controlled combinations of operating parameters, such as fuel equivalence ratio (?), fuel mixture flow rate, plasma gas flow rate, plasma gases, symmetric or asymmetric fuel-oxidant injection patterns, with and without plasma. In this work, ignitions at the fuel (lean and rich) flammability limits at different plasma powers and fuel flow rates were investigated. The ignition curves of plasma power versus ?_FL at the different flow rates revealed a stretched U-shape, showing clear evidences of the plasma enhancement effects on ignition and flame stabilization, i.e. the fuel lean flammability limit (?_LFL) was extended to ? = 0.2, as compared to ? = 0.6 at the same combustion parameters except with no plasma. Optical emission spectroscopy (OES) showed that the combustor had three distinct reaction zones: plasma zone, hybrid plasma-flame zone, and flame zone; and each of the reaction zones was well defined by its OES features. Furthermore, a detailed survey of OES of OH (A–X) conducted along the plasma jet axis (x direction) with a spatial resolution of 0.5 mm revealed that OH(A) had a double-peak feature in its relative emission intensity curve (I ∼ x) in the hybrid zone where plasma-assisted ignition (PAI) started, as evidenced by a significant surge of OH(A) and by a large increase in OH rotational temperature, i.e. from 1450 K to 2400 K. Moving from the hybrid zone to the flame zone, OH(A) decreased by more than four orders of magnitude. However, the electronic ground state OH(X) measured simultaneously using pulsed cavity ringdown spectroscopy around 308 nm showed that absolute number density of the OH(X) decreased by smaller than a factor of ten from the downstream of the hybrid zone to the flame zone. The different changing rates of the OH(A) and OH(X) radicals from the hybrid zone to the flame zone allow us to propose a hypothesis that if both the electronically excited state OH(A) and the electronic ground state OH(X) assisted the ignition and flame stabilization processes, the role of OH(X) radicals was more dominant in the flame stabilization but the role of OH(A) radicals was more dominant in the ignition enhancement.     

Detailed transient numerical simulation of H2/air hetero-/homogeneous combustion in platinum-coated channels with conjugate heat transfer

Transient two-dimensional simulations of fuel-lean H₂/air combustion were performed in a 2-mm-height planar channel coated with platinum, using detailed hetero-/homogeneous chemistry and transport as well as heat conduction in the solid wall. The developed model resolved, for the first time, all relevant spatiotemporal scales in a practical channel-flow reactor configuration. A parametric study was carried out to investigate the effects of wall material, inlet velocity, and inlet temperature on the fundamental catalytic and gas-phase combustion processes. Computational singular perturbation (CSP) analysis identified the key catalytic reactions affecting light-off and homogeneous ignition. Homogeneous ignition crucially depended on the OH desorbing fluxes from the catalyst, while flame propagation and stabilization involved time scales of a few milliseconds. During the short duration of the light-off event, the ensuing Stefan velocity appreciably altered the flow field. Predictions of time accurate numerical simulations were further compared against those of a code relying on the quasisteady state assumption, and the specific conditions under which the latter was invalidated were identified. Finally, CSP analysis unraveled the reasons for the high computational cost of the fully transient 2-D simulations. The surface reaction mechanism exhibited a high stiffness with fastest time scales of the order of 10^-12${10}^{-12}$ s, pertaining to the hydrogen adsorption and to the H(s) + O(s) = OH(s) + Pt(s) reactions. These time scales were in turn six orders of magnitude shorter than the ones associated with gas-phase chemistry or with a simplified single-step catalytic reaction.