Further Improvements

Further improvements can be expected by including the effects of intermediate species and radiation, both of which will result in lower predicted combustion temperatures.

The single-step reaction process used in this tutorial cannot account for the moderating effects of intermediate reaction products, such as CO and H $_2$. Multiple-step reactions can be used to address these species. If a multi-step Magnussen model is used, considerably more computational effort is required to solve for the additional species. Where applicable, the nonpremixed combustion model can be used to account for intermediate species at a reduced computational cost.

For more details on the nonpremixed combustion model, see this chapter in the separate User's Guide.

Radiation heat transfer tends to make the temperature distribution more uniform, thereby lowering the peak temperature. In addition, radiation heat transfer to the wall can be very significant (especially here, with the wall temperature set at 300  ${\rm K}$). The large influence of radiation can be anticipated by computing the Boltzmann number for the flow:

where $\sigma$ is the Boltzmann constant (5.729 $\times 10^{-8}$  ${\rm W/m}^2{\rm -K}^4$) and $T_{AF}$ is the adiabatic flame temperature. For a quick estimate, assume $\rho=1$  ${\rm kg/m}^3$, $U=0.5$  ${\rm m/s}$, and $C_p = 1000$  ${\rm J/kg-K}$ (the majority of the inflow is air). Assume $T_{AF} = 2000$  ${\rm K}$. The resulting Boltzmann number is Bo = 1.09, which shows that radiation is of approximately equal importance to convection for this problem.

For details on radiation modeling, see this section in the separate User's Guide.

This tutorial guides you through the steps to reach an initial set of solutions. You may be able to obtain a more accurate solution by using an appropriate higher-order discretization scheme and by adapting the mesh. Mesh adaption can also ensure that the solution is independent of the mesh. These steps are demonstrated in Tutorial  1.