Numerical simulation is an effective tool for studying combustion

in which the combustion model influences the results significantly. In turbulent combustion

the reaction rate not only depends on the local concentration of reactants and temperature

but also the turbulent condition. The algebraic second-order moment model (ASOM) can consider these conditions and is simpler than other models. In this study

mixing rate is considered in a modified ASOM model (RASOM). The reaction rate is calculated more accurately with RASOM in a partially stirred reactor

using the chemical time scale and the mixing time scale to demonstrate the influence of mixing rate. Simulations for a piloted methane/air diffusion flame (Sandia flame D) are carried out to verify the model. RASOM and eddy break-up model are applied in the simulations. The results are compared to experimental data of the mean axial velocity

average temperature

and mass fraction of O2. Results from ASOM are also used in the comparison. Although the RASOM predicts the result improperly at some locations

it is more appropriate than EBU-A and ASOM. And the effect of mixing rate on the reaction rate in RASOM is discussed in detail.