LES study of nongray radiation effects on an ammonia swirl flame in a confined combustor

Radiative effects in a gas-phase ammonia swirl combustor are investigated using large-eddy simulations (LES) coupled with a physics-informed neural network-accelerated full-spectrum correlated- k -distribution radiation model (PINN-FSCK) (Di et al., 2026). The radiation characteristics predicted by PINN-FSCK are compared with those obtained using a gray radiation model (GRAY) and without any radiation model (NRAD). The resolved turbulence–radiation interaction (TRI) is also evaluated by comparing the mean radiative source term obtained from instantaneous LES fields with a reference source term reconstructed from mean thermochemical fields. Results indicate that PINN-FSCK preserves the global topology of the swirl flame while producing a spatially nonuniform coupled thermal response. The central product core is warmer over much of the mean field, whereas local temperature reductions occur along the outer flame and shear-layer regions. H 2 O-rich hot products dominate radiative emission, while low-temperature NH 3 -containing layers absorb part of the emitted radiation. Although GRAY predicts a similar mean flame shape, it distorts the local radiative energy partition by overestimating absorption in ammonia-containing low-temperature regions, thereby introducing local temperature biases. Furthermore, the resolved TRI is not globally significant but becomes locally important near flame edges, shear layers, and vortical structures. These results demonstrate that nongray radiation modelling is essential for accurately predicting local thermal energy redistribution in ammonia swirl flames, whereas TRI should be treated as a localized radiation-closure issue.