In this chapter, the ignition, combustion, and pollutant formation of solid fuel particles under different operating conditions are investigated using detailed numerical simulations. First, coal and biomass combustion in a laminar flow reactor configuration are compared, showcasing similar combustion characteristics between coal and biomass. Then, particle/particle interaction effects in the particle group configuration are investigated, indicating later ignition time and flame opening behaviour in higher particle number densities. Particle/chemistry/turbulence interactions are also studied in particle cloud combustion under isotropic turbulence, where ignition is found to occur most likely outside of particle clusters. To assess the reduced-order flamelet models for solid fuel combustion, the optimal estimator concept is employed using the generated dataset, revealing that modelling errors increase near particles. Finally, NO \(_x\) formation during solid fuel combustion is analysed. The highest NO \(_x\) formation is found to occur near the particle groups around stoichiometric mixtures. Important pathways for NO \(_x\) formation under different operating conditions are studied, revealing the dominance of the fuel-NO \(_x\) pathways.