An Updated Weighted-Sum-of-Gray-Gases Model for Radiation Calculation of H2/NH3 Flames in High-Pressure Conditions

Developing zero-carbon energy systems fueled by hydrogen and ammonia is crucial for modern aerospace propulsion. As operational temperatures frequently exceed 1000 °C, thermal radiation becomes the dominant heat transfer mechanism. Furthermore, elevated operating pressures (up to 20 bar) trigger intense collisional broadening and significantly increase the overall optical thickness. Traditional radiative models inadequately characterize these environments by neglecting the substantial radiative contribution of unburned NH3. To overcome such limitations, a novel pressure-dependent weighted-sum-of-gray-gases (WSGG) model incorporating a variable total radiation gas concentration is developed specifically for estimating the radiation of H2/NH3 flames in high-pressure conditions. With its parameters optimized via sequential quadratic programming (SQP), the proposed model is rigorously validated against benchmark line-by-line (LBL) calculations across isothermal, nonisothermal, and nonhomogeneous conditions. The updated WSGG framework demonstrates exceptional accuracy, maintaining average relative errors firmly within 10%. Ultimately, the newly developed model provides a highly reliable and efficient method for evaluating radiative heat transfer characteristics of zero-carbon fuels under engine-like conditions.