Numerical Investigation of Thermal Field Characteristics in an EGR-Assisted Methane–Hydrogen Co-Fired Radiant Tube Burner

Radiant tube burners (RTBs) are widely used in industrial heat-treatment furnaces, yet the coupled effects of hydrogen co-firing and exhaust gas recirculation (EGR) on their thermal fields remain insufficiently understood. This study presents a three-dimensional CFD analysis of 28 operating conditions, spanning hydrogen fractions from 0 to 100% and EGR rates from 0 to 20% at a fixed excess air ratio of 10%. The model employs the eddy dissipation concept with a reduced two-step methane mechanism, detailed hydrogen kinetics, and a Discrete Ordinates radiation model with a weighted-sum-of-gray-gases approach. All cases exhibit splitting flames: hydrogen enrichment intrinsically raises the laminar flame speed above the flame morphological transition threshold, while in pure methane, radiative preheating increases the flame speed by 29%, eliminating the triangular flame mode. The volumetric temperature uniformity index peaks near 30% H2, whereas EGR improves uniformity in hydrogen-rich cases but slightly degrades it in methane-rich conditions. Surface temperature uniformity is maximized at 20% EGR due to near-wall thermal blanketing. Thermal efficiency increases with hydrogen fraction, from 59.1% at 0% H2 without EGR to 68.6% at 100% H2 with 10% EGR, while higher EGR suppresses peak temperatures. These findings provide guidance for balancing energy efficiency and temperature uniformity in hydrogen-ready RTBs.