This article presents a numerical investigation of flameless combustion focusing on assessment of turbulence, combustion and radiation modelling. The commercial code ANSYS FLUENT 19.0 is used to solve 3-D computational equations. Local measurements across a small lab cylindrical flameless combustor burning methane fuel were used for validation. Five different turbulence models were employed, namely realizable k- Ԑ, shear stress transport k-Ꞷ) SST k-Ꞷ (, RNG k- Ԑ, Reynolds Stress Model) RSM (and transition SST. Results of RNG k- Ԑ turbulence model were achieved a good agreement with the experimental data. The research focuses on assessment of several models for chemical kinetics and combustion simulations. Four numerical models were used namely Eddy Dissipation Concept (EDC), Finite-Rate/Eddy-Dissipation (FR/ED), combination of EDC with reduced mechanisms based on GRI-Mech 3.0 (GRI-EDC) and modified GRI-Mech 3.0. EDC combustion model was showed a good predication of mean temperature and mean dry basis volume fraction of O2 and CO2 emissions, but it cannot solve CO emissions. Generally, GRI-EDC was the best model for simulating the flameless combustion which have the ability to obtain better prediction of all characteristics. Moreover, the issue of radiation modelling was implemented and results were compared in three cases, no radiation, P1 model and Discrete Ordinates (DO) radiation model. It was concluded that the radiation modelling does not yield significant differences in numerical prediction of mean temperature and species.