Combustion is governed by only two phenomena: chemical reactions and mixing (i.e., transport of energy, species, and momentum). A Reynolds Averaged Navier-Stokes (RANS) turbulence model is commonly employed to account for the enhanced mixing due to the presence of turbulence in fluid flow. A RANS turbulence model enhances mixing by introducing a turbulent viscosity. The addition of a turbulent viscosity not only enhances mixing but it also eliminates smaller scales in the CFD simulation. Even though the turbulent viscosity eliminates smaller scales, it is common for RANS engine combustion simulations to be under-resolved. The lack of sufficient mesh resolution to resolve the remaining scales in a RANS combustion simulation may result in a significant sub-grid term that needs to be modeled. In the context of combustion simulation, it is shown that frequently this sub-grid term is significantly more important than Turbulent Chemistry Interaction terms (TCI). It is also shown that by adding sufficient mesh resolution to a RANS simulation, accurate combustion results can be obtained by using detailed chemistry directly.