Investigation of Radiative Characteristics of Gases and Development of a Weighted-Sum-of-Gray-Gases Model for Hydrogen Combustion

Under the dual-carbon strategy, green hydrogen as a zero-carbon fuel is rapidly expanding in engineering applications. However, the absence of gas radiation models specifically validated under high H₂O mole fraction, pure H₂ combustion conditions compromises the accuracy of radiation calculations in hydrogen-fueled thermal systems. To bridge this gap, 43,680 line-by-line calculations spanning the full operating space were performed using the HITEMP2010 database. These calculations systematically quantify the effects of temperature, total pressure, radiation path length, and H₂O mole fraction on the emissivity of pure hydrogen combustion gases. Based on this high-fidelity benchmark dataset, a novel four-gray-gas weighted-sum-of-gray-gases model (WSGGM) applicable at 1 atm was developed using the Levenberg–Marquardt algorithm, covering 500–3000 K, 0.01–60 m, and 1–100% H₂O mole fraction. The results establish the following influence hierarchy: radiation path length > temperature > H₂O mole fraction > total pressure. Radiation path length dominates across all temperatures. Emissivity exhibits three-stage saturation growth with increasing radiation path length, with 56.1% of the total increment occurring within the first 5 m at 500 K. At a radiation path length of 10 m and 30% H₂O mole fraction, emissivity decreases monotonically with temperature, dropping by 80.7% from 500 to 3000 K (1 atm). Emissivity is most sensitive to H₂O mole fractions below 0.1, whereas pressure exerts the weakest influence, with its effect saturating above 10 atm. The WSGGM fits total emissivity with excellent accuracy (R² = 0.999820, MAE = 0.002153) and is directly implementable in mainstream CFD software, providing a ready-to-use radiation model for high-fidelity simulation and design of hydrogen-fueled thermal systems.