Effects of catalytic walls on hydrogen/air combustion inside a micro-tube

Chen, Guan Bang; Chen, Chih Peng; Wu, Chia Ching; Chao, Yei Chin

doi:10.1016/j.apcata.2007.08.011

Cited by 89 publications

(44 citation statements)

References 10 publications

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“…The steady state time increases as the wall thermal conductivity is increased. For low wall thermal conductivity, a high temperature gradient exists on the wall, which will make the homogeneous combustion shift upstream and the micro-combustor will have a higher peak temperature (Chen et al, 2007). On the contrary, for high wall thermal conductivity, a low temperature gradient on the wall will make the homogeneous combustion shift downstream and the micro-combustor will have a higher outlet temperature.…”

Section: Transient Behaviormentioning

confidence: 92%

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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Section: Transient Behaviormentioning

confidence: 92%

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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“…Most previous computational studies dealt with surface catalytic or gas phase reaction separately and concentrated on the flame stability or extinction limit (Chen et al, 2007;Deutschmann et al, 2012;Ju and Maruta, 2011;Kamijo et al, 2009;Karagiannidis and Mantzaras, 2010;Maruta, 2011). Although the catalyst is used to maintain the reaction and to decrease the heat loss, the effect of thermal conductivity on micro-combustion characteristics and the interaction between surface catalytic and gas phase reaction in micro-combustors are still not fully understood.…”

Section: Frontiers In Heat and Mass Transfermentioning

confidence: 99%

EFFECT OF WALL THERMAL CONDUCTIVITY ON MICRO-SCALE COMBUSTION CHARACTERISTICS OF HYDROGEN-AIR MIXTURES WITH DETAILED CHEMICAL KINETIC MECHANISMS IN Pt/γ-Al2O3 CATALYTIC MICRO-COMBUSTORS

Chen¹,

Liu²,

Song³

2014

Frontiers in Heat and Mass Transfer

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To understand the effect of different thermal conductivities on catalytic combustion characteristics, effect of thermal conductivity on micro-combustion characteristics of hydrogen-air mixtures in Pt/γ-Al2O3 catalytic micro-combustors were investigated numerically with detailed chemical kinetics mechanisms. Three kinds of wall materials (100, 7.5, and 0.5 W/m·K) were selected to investigate the effect of heat conduction on the catalytic combustion. The simulation results indicate that the catalytic reaction restrains the gas phase reaction in Pt/γ-Al2O3 catalytic micro-combustors. The gas phase reaction restrained by Pt/γ-Al2O3 catalysts is sensitive to thermal boundary condition at the wall. For most conditions, the gas phase reaction cannot be ignored in Pt/γ-Al2O3 catalytic micro-combustors. For low thermal conductivity, the higher temperature gradient on the wall will promote the gas phase reaction shift upstream; high temperature gradient exists on the wall, and the hot spot can cause the material to melt or degrade the catalyst. Due to the gas phase reaction is ignited and sustained in micro-combustors by the heat from the catalytic reaction, the effect of thermal conductivity on micro-scale combustion characteristics is not as obvious as it is in micro-combustors without Pt/γ-Al2O3 catalysts.

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“…The wall having a much lower temperature than the center of the flame creates a thermal gradient causing heat and reactive species to diffuse towards the wall, which in turn causes the local laminar flame speed at the wall to be lower than that at the center of the passage [12]. The behavior and stability of the flame is controlled by the heat loss to the walls and the heat release rate of the flame, hence the fuel mixture is varied to achieve a favorable condition for stable operation [7,13].…”

Section: Flame Propagationmentioning

confidence: 99%