The flow dynamics of producer gas premixed charge in a cyclone combustor was investigated using the computational fluid dynamic modeling. Two main variables to achieve high swirl flow and reactant dilution were the flow rate of the reactants and nozzle diameter. The first variable showed a considerable effect on the in-combustor residence time reducing from 0.64 to 0.44seconds when the reactant flow rate increases from 0.037 to 0.057kg/second. While its effect on the swirl flow distribution and flameless conditions was not significant, as indicated by the steady swirl number and reactant dilution degree averaging 2.5% and 58%, respectively. On the other hand, decreasing the nozzle diameter from 50 to 20mm was more beneficial for the enhancement of reactant dilution and swirl flow distribution as they increased from 58% to 78% and 2.5 to 3.4, respectively. The result also showed that reducing the nozzle diameter below 40mm is suitable for the present configuration of the combustor to be effectively operated in flameless combustion mode. However, the smallest diameter (20mm) resulted in more fluctuations of the axial velocity profile, which may lead to highly turbulent fluid dynamic features.