This study numerically investigates the effect of catalytic activity on the cold-start ignition and combustion characteristics of a propane-fueled U-bend catalytic micro-reactor. A reactive-wall approach is employed to model the catalyst coating, wherein catalytic activity is represented by the surface area factor. The results show that surface area factors between 0.425 and 3.4 exert a significant impact on ignition and combustion behavior, reducing the ignition temperature from 682 K to 521 K and decreasing the ignition delay time from 147 s to 52 s while increasing the HTR (heterogeneous reaction) contribution from 26.1% to 65.5%. Beyond a surface area factor of 3.4, performance improvements become marginal. The temporal analysis reveals that the catalytic reaction pathway dominates during the preheating stage, whereas the gas-phase reaction pathway gains prominence following ignition, eventually reaching a stable balance between the two pathways after approximately 10 s. These findings identify low catalytic activity as a sensitive operating regime and underscore the critical role of catalytic activity in optimizing ignition performance of catalytic micro-reactors.

Leveraging catalytic microreactors as compact yet powerful thermal sources represents a promising approach to enable rapid and reliable startup of small-scale solid oxide fuel cell (SOFC) systems. In the present study, the homogeneous–heterogeneous (HH) combustion behavior of a propane/air mixture in a Pt-catalyzed microreactor is investigated using two-dimensional computational fluid dynamic (CFD) simulations. The catalytic reaction kinetics model is integrated into the general module of ANSYSY Fluent via a user-defined function (UDF) interface. By varying the surface area factor, the ignition characteristics of the propane/air mixture under different catalyst activities are systematically explored. Numerical results reveal that the relative catalyst activity range of 0–2 represents a sensitive region for propane/air ignition characteristics, characterized by a 541 K decrease in ignition temperature and a 50% reduction in ignition delay time. Nevertheless, further increases in relative catalyst activity from 2 to 10, yield a much smaller reduction—64 K in ignition temperature and 6.7 s in ignition delay time—indicating a weakly responsive regime. The relative contribution of the heterogeneous reaction (HTR) to the total heat release decreases with higher feed temperatures but increases with enhanced catalyst activity. Regarding the temporal evolution of HTR contribution, the initiation of homogeneous ignition undermines the dominance of HTR contribution. Irrespective of catalytic activity levels, the relative contributions of the two reaction pathways subsequently undergo dynamic redistribution and ultimately stabilize, reaching an equilibrium state within approximately 10 s. These findings provide critical insights into the role of catalyst activity in propane/air mixture ignition and the interplay between homogeneous and heterogeneous reactions in microscale combustion systems.

This paper presents a numerical comparative study on the ignition characteristics of straight-channel and U-bend micro catalytic combustors, with particular focus on the role of inlet velocity. A two-dimensional computational fluid dynamics model with coupled gas-phase and surface catalytic reaction kinetics for propane combustion is developed using a fluid simulation program ANSYS Fluent. The catalyst coating (Pt/Al₂O₃) is modeled as a zero-thickness reaction surface, and the U-bend design features an uncoated recirculating channel to ensure identical catalyst loading between the two configurations. Simulations are conducted over an inlet velocity range of 0.25–8 m/s. Key ignition and combustion metrics including ignition temperature, ignition time, maximum combustion temperature, heterogeneous reaction contribution, and thermal/species field distributions are systematically compared. Results reveal a crossover in relative performance depending on flow regime. At low velocities (≤2 m/s), the straight-channel combustor exhibits lower ignition temperatures; at high velocities (≥4 m/s), the U-bend design achieves superior ignition performance with lower ignition temperatures (e.g., 526 K vs. 555 K at 8 m/s) and higher combustion temperatures (1726 K vs. 1474 K at 8 m/s). However, the straight-channel combustor consistently yields shorter ignition times across all velocities (25.9–108.6 s) compared to the U-bend (52.6–145.2 s). The heterogeneous reaction contribution decreases with increasing inlet velocity for both designs, with the straight-channel maintaining higher values than the U-bend. The U-bend achieves higher maximum temperatures due to enhanced heat recirculation, particularly at high flow rates. The findings suggest that the U-bend configuration is advantageous for high-flow-rate applications requiring low ignition temperatures and high combustion temperatures, whereas the straight-channel design is preferable for rapid cold-start scenarios.

Radiant porous burners are favored in household and industrial applications for their high flexibility, minimal emissions, and excellent fuel adaptability. Enhancing heating temperature uniformity improves the heat transfer efficiency and heating quality. This work presents a two-dimensional numerical study on the non-uniformity of the heating temperature (i.e., solid temperature at the burner exit) in a cylindrical porous burner. The root mean square (RMS) of the heating temperature ($T_{\mathrm{s},\mathrm{rms}}$) is used to quantify the non-uniformity. From the numerical results, the cylindrical porous burner exhibits a non-uniform heating temperature and a non-uniform mass flow rate of flue gas at the sub-outlets. The surface emissivity and equivalence ratio have minor effects on the $T_{\mathrm{s},\mathrm{rms}}$. However, increasing the volumetric flow rate and solid temperature leads to a more uniform distribution of heating temperature. The $T_{\mathrm{s},\mathrm{rms}}$ decreases from 40 K to 4.4 K as the volumetric flow rate increases from 26.75 slm (standard liters per minute) to 87 slm at an equivalence ratio of 0.96 and emissivity of 0.85. Meanwhile, the results demonstrate that increasing the thermal conductivity of the porous shell improves the heating temperature uniformity. This study presents guidelines for enhancing the uniformity of heating temperature for the cylindrical porous burner.

Catalytic micro-reactors offer a promising solution for portable power generation, yet catalyst deactivation during long-term operation remains a critical challenge to reliable ignition and combustion stability. In this work, a transient numerical model is developed to conduct a sensitivity study of ignition and combustion performance to catalyst deactivation, represented as prescribed reductions in catalytic activity, for a propane-fueled straight-channel micro-combustor. The present model explicitly resolves the porous catalyst coating layer as a separate computational domain, incorporating a combined Knudsen and molecular mixed-diffusion mechanism to capture species transport resistance within the microporous structure. The results demonstrate that increasing catalyst deactivation markedly deteriorates ignition performance. As the deactivation index rises from 0.1 to 0.9, the ignition temperature increases from 488 K to 588 K in a distinctly nonlinear manner, with the greatest sensitivity observed at high deactivation levels. At inlet temperatures 10 K above the respective ignition thresholds, the ignition delay time is prolonged from 191 s to 224 s when the deactivation index increases from 0.7 to 0.9, attributed to the dominance of kinetic deterioration over sensible heat compensation. The heterogeneous reaction contribution, although decreasing with deactivation, remains above 95% across all cases, indicating that the gas-phase pathway is largely suppressed due to the inherently low temperature environment within the microchannel. Spatial distributions of temperature and CO₂ mass fraction reveal that combustion is confined to the near-inlet region, with a peak temperature of approximately 1001 K at the highest deactivation level. These findings quantify the sensitivity of ignition and combustion characteristics to catalyst deactivation.

The global effort to mitigate hazardous particulate matter (PM) emissions from diesel engines relies significantly on advances in separations technologies. The diesel particulate filter (DPF) is a critical component designed to trap soot and ash from diesel engine exhaust, ensuring cleaner emissions and compliance with environmental regulations. In the current paper, a gas-particle two-phase flow model in the microchannels of a DPF is developed. A novel statistical approach based on probability sampling is proposed aimed at generating a particle ensemble that adheres to the real-world soot particle size distribution (PSD). The Eulerian-Lagrangian approach is employed to model the soot-laden gas flow, where the gas phase flow field is solved in the Eulerian framework, while the particle phase motion is tracked in the Lagrangian framework. The results demonstrate that the through-wall velocity plays a predominant role in the overall deposition behavior of the mixed-sized particle group. Increasing upstream velocity shifts initial particle deposition positions further from the channel inlet and enhances mass accumulation at the channel’s terminal section. Reduced filtration wall permeability promotes the uniformity of soot deposition along the channel. A permeability of 5 × 10⁻¹³ m² is identified as the critical threshold, below which the soot deposition distribution approaches near-complete uniformity.