Search Results (4)

Micro-combustion-powered thermoelectric generators (μ-CPTEGs) combine the high energy density of hydrocarbons with solid-state conversion, offering compact and refuelable power for long-endurance electronics. Such characteristics make μ-CPTEGs particularly promising for aerospace systems, where conventional batteries face serious limitations. Their achievable performance hinges on how a swirl-stabilized flame transfers heat into the hot ends of thermoelectric modules. This study uses a conjugate CFD framework coupled with a lumped parameter model to examine how input power and equivalence ratio shape the flame/flow structure, temperature fields, and hot-end heating in a swirl combustor-powered TEG. Three-dimensional numerical simulations were performed for the swirl combustor-powered TEG, varying the input power from 1269 to 1854 W and the equivalence ratio from φ = 0.6 to 1.1. Results indicate that the combustor exit forms a robust “annular jet with central recirculation” structure that organizes a V-shaped region of high modeled heat release responsible for flame stabilization and preheating. At φ = 1.0, increasing Q_in from 1269 to 1854 W strengthens the V-shaped hot band and warms the wall-attached recirculation. Heating penetrates deeper into the finned cavity, and the central-plane peak temperature rises from 2281 to 2339 K (≈2.5%). Consistent with these field changes, the lower TEM pair near the outlet heats more strongly than the upper module (517 K to 629 K vs. 451 K to 543 K); the inter-row gap widens from 66 K to 86 K, and the incremental temperature gains taper at the highest power, while the axial organization of the field remains essentially unchanged. At fixed Q_in = 1854 W, raising φ from 0.6 to 1.0 compacts and retracts the reaction band toward the exit and weakens axial penetration; the main-zone temperature increases up to φ = 0.9 and then declines for richer mixtures (peak 2482 K at φ = 0.9 to 2289 K at φ = 1.1), cooling the fin section due to reduced transport, thereby identifying φ = 0.9 as the operating point that best balances axial penetration against dilution/convective-cooling losses and maximizes the TEM hot-end temperature at the fixed power. Full article

This research presents a novel bluff-body and swirl-stabilized micro-combustor fueled by an ammonia/hydrogen mixture, aimed at enhancing flame stabilization for zero-carbon micro-combustion-based power generators. Employing numerical simulations, the study examines the effects of bluff-body geometry, inlet mass flow rate, vane angle, and combustor material on combustion and thermal efficiencies. Key findings demonstrate that the shape of the bluff-body significantly influences the combustion outcomes, with cone-shaped designs showing the lowest radiation efficiency among the tested geometries. The study identifies an optimal inlet mass flow rate of $9\times {10}^{-6} \mathrm{k}\mathrm{g}/\mathrm{s}$, which achieves a combustion efficiency of 99% and superior uniformity in the mean outer wall temperature. While variations in flow rate primarily affect NO emissions and outer wall temperatures, they have minimal impact on combustion efficiency. Further analysis reveals that adjusting the vane angle from 15 to 60 degrees significantly improves mean outer wall temperatures, temperature uniformity, and combustion and radiation efficiencies, while also reducing NO emissions. The 60-degree angle is particularly effective, achieving approximately 44% radiation efficiency. Additionally, material selection plays a pivotal role, with silicon carbide outperforming others by delivering an optimized mean outer wall temperature (approximately 910 K), radiation efficiency (38.5%), and achieving the most uniform outer wall temperature. Conversely, quartz exhibits significantly lower thermal performance metrics. Full article

In order to implement moderate or intensive low oxygen dilution (MILD) combustion, it is necessary to extend the flame stability and operating range. In the present study, the conceptual designs of a combustor single nozzle and reformer were numerically suggested for a micro-gas turbine with an on-board reformer. The target micro-gas turbine achieved a thermal power of 150 kW and a turbine inlet temperature (TIT) of 1200 K. Studies on a nozzle and reformer applying an open-loop concept have been separately conducted. For the nozzle concept, a single down-scaled nozzle was applied based on a reference nozzle for a heavy-duty gas turbine. The nozzle can achieve a good mixture with a high swirl with a splined swirl curve lower NOx emissions and smaller pressure drop in the combustor. The concept of the non-catalytic partial-oxidation reforming reformate was designed using the combustor outlet temperature (COT) of the exhaust gas. Feasible hydrogen yields were mapped through the reformer. Based on the hydrogen yields from the reformer, hydrogen was added to the nozzle to investigate its combustion behavior. By increasing the hydrogen addition and decreasing the O₂ fraction, the OH concentrations were decreased and widely distributed similar to the fundamental characteristics of MILD combustion. Full article

Improving the flame stability and thermal behavior of the micro-combustor (MC) are major challenges in microscale combustion. In this paper, the micro combustions of an H₂/air premixed flame in a swirl MC with various channel diameters (D_in = 2, 3, 4 mm) were analyzed based on an established three-dimensional numerical model. The effects of hydrogen mass flow rate, thermal conductivity of walls, and the preferential transport of species were investigated. The results indicated that the flame type was characterized by the presence of two recirculation zones. The flame was anchored by the recirculation zones, and the anchoring location of the flame root was the starting position of the recirculation zones. The recirculation zones had a larger distribution of local equivalence ratio, especially in the proximity of the flame root, indicating the formation of a radical pool. The combustion efficiency increased with an increasing D_in due to the longer residence time of the reactants. Furthermore, the MC with D_in = 2 mm obtained the highest outer wall temperature distribution. However, the MC with D_in = 4 mm had a better uniformity of outer wall temperature and large emitter efficiency due to the larger radiation surface. An increase in thermal conductivity boosts the thermal performance of combustion efficiency, emitter efficiency, and wall temperature uniformity. But there is a critical point of thermal conductivity that can increase the thermal performance. The above results can offer us significant guidance for designing MC with high thermal performance. Full article