Numerical investigation of radiative heat transfer effects on liquid ammonia jet spray flames

Abstract

Radiative heat transfer in liquid-ammonia spray flames remains poorly understood, particularly because liquid evaporation, fuel-side mixing, and product-side heat release are spatially separated. In this study, radiative heat transfer in a spatially developing liquid-ammonia jet spray flame is investigated using an Eulerian–Lagrangian large-eddy simulation framework coupled with full-spectrum correlated- k (FSCK) nongray radiation modeling. Non-radiative and gray-radiation cases are also considered to isolate the effects of radiation and spectral treatment. The results show that radiative energy is mainly emitted from the downstream and surrounding H 2 O-rich high-temperature product region and is partly absorbed by the upstream low-temperature NH 3 -rich fuel/spray mixing region. After strong flash evaporation and phase-change cooling weaken, this fuel-side absorption produces radiative preheating along the NH 3 -rich gaseous centerline region, while parts of the downstream product region undergo radiative emission cooling. The resulting radiation-induced temperature differences reach the order of 1 0 2 K locally and also affect the dispersed phase by enhancing the droplet temperature-change rate in the upstream and intermediate spray regions. The local-Planck-mean gray model preserves the qualitative flame topology but substantially overpredicts radiative absorption in the low-temperature NH 3 -rich region, leading to excessive fuel-side preheating with Gray–FSCK temperature differences of approximately 80–100 K. Although NH 3 is a weaker absorber than H 2 O, its spectrally selective absorption in the fuel-side region cannot be represented accurately by a single local Planck mean. These results demonstrate that nongray radiation modeling is required not only for H 2 O-rich product-side emission, but also for NH 3 -rich low-temperature absorption and its coupling with the dispersed liquid phase in medium- and large-scale liquid-ammonia spray flames. Novelty and significance statement: This work presents, to the best of the authors’ knowledge, the first systematic study of radiative heat-transfer effects in a spatially developing liquid-ammonia jet spray flame. It identifies the low-temperature NH 3 -rich spray/mixing region as an important nongray absorption zone, although it is not the dominant emitter. The results show that local-Planck-mean gray treatment misrepresents this fuel-side absorption and causes significant temperature bias, demonstrating the need for nongray radiation modeling in liquid-ammonia spray-flame simulations.