Numerical Study of Heat Recirculation on Combustion Performance and Thermal Efficiency in a Novel Hydrogen–Air Micro-Combustor

Micro-scale combustion systems integrated with hydrogen fuel and thermophotovoltaic (TPV) technology provide a promising solution for compact and efficient power generation. In this study, premixed hydrogen–air combustion is numerically investigated in an MIT-inspired micro gas turbine combustion chamber featuring combined curvature, expansion, and contraction, enabling enhanced flame stabilization and reactant preheating. A three-dimensional numerical model is developed to analyze the influence of inlet flow velocity, equivalence ratio, and wall thermal conductivity on combustion behavior and system performance. The results show that increasing inlet velocity from 4 m/s to 8 m/s reduces thermal efficiency from 12.27% to 10.56% due to shorter residence time. Higher velocities also shift the flame downstream and increase peak OH concentration, indicating intensified but less complete reactions. Variations in equivalence ratio reveal that maximum temperature and OH mass fraction increase as the mixture approaches stoichiometric conditions, reaching peak values of 1934 K and 0.0102 at φ = 1, and then decrease under rich conditions due to oxygen limitation. In addition, the flame location shifts significantly toward the inlet as φ increases. Thermal conductivity demonstrates a competing effect: increasing conductivity from 1.4 to 6.7 W/m·K improves efficiency (up to 9.05%) and enhances temperature uniformity through better heat redistribution, while further increases to 12.63 W/m·K reduce peak solid temperature and slightly decrease efficiency due to excessive heat loss. Higher conductivity also shifts the flame upstream and increases OH concentration by strengthening preheating and reaction rates