With respect to radiative property modelling, one of the most difficult aspects is the spectral dependence. Spectral resolution of gas and particle properties included in the solution is directly reflected on the computational cost of the global model as it directly determines the number of intensity equations (RTE) to be solved.

Divergence of radiative heat flux fields obtained with gray and non-gray radiation models for methane–air diffusion flame [1]

Although a wide variety of gas spectral radiative property models with different degrees of complexity and accuracy are available in the literature, there are relatively much fewer studies in the literature where spectral particle properties are considered together with spectral gas properties. For fuel/ash particles, number of studies which involves both spectral gas and particle properties are limited to the narrow band models, which requires a tremendous amount of CPU time.

Ates et al. (2018) have recently introduced two accurate and CPU efficient spectral gas radiation models,) which are compatible with spectral fuel/ash particle property models. They modified well-known global SLW model and introduced a new model, banded-SLW, which is demonstrated to be as accurate as global SLW model for gas radiation. With their banded-SLW approach, they have shown that it is possible to alleviate the need for narrow band models requiring excessive CPU time by reducing the number of intensity equations to be solved to evaluate spectral particle radiation. They also investigated a simpler approach, called Gray Wide Band approximation (GWB), and demonstrated that GWB can be used to reduce the CPU requirement of the model significantly without losing much accuracy if the order of magnitude of the particle absorption coefficient is higher than that of gas absorption coefficient.

C.Ates, G. Ozen, N. Selçuk, G. Kulah, Assessment of Gas Radiative Property Models in the Presence of Non-gray Particles, Numerical Heat Transfer Part A: Applications, 73, (2018), pp. 385-407 (https://doi.org/10.1080/10407782.2018.1447196). 

[1] N. Selçuk, A.B. Uygur, I. Ayrancı, T. Tarhan, Transient Simulation of Radiating Flows. Journal of Quantitative Spectroscopy and Radiative Transfer, 93, (2005), pp.151-161 (https://doi.org/10.1016/j.ijthermalsci.2006.01.008).