Numerical study of the effect of H_2O diluents on NO_X and CO formation in turbulent premixed methane-air flame

摘要

The interaction of turbulenceecombustion inside the flame field is studied in a Launder-Sharma Low Reynolds Number (LS-LRN) k-epsilon/EDM framework, while suitable coefficients have been utilized in the code. A finite volume method (FVM) with staggered grids was applied to discrete set of governing equations. SIMPLE algorithm is applied with a fine grid resolution. The convective terms are discretized using Power Law Scheme (PLS). The system of governing equations is solved simultaneously using numerical or TDMA finite difference methods (Tri-Diagonal Matrix Algorithm). By implementation of the Zeldovich and Westbrook-Dryer mechanisms, NOx and CO concentrations were obtained, respectively. It is illustrated that the implemented LS-LRN-k-epsilon/EDM method with the new coefficients by shorter runtimes has very good agreement with previously published experimental measurements. Increasing the H2O diluent at the inlet leads to an increase in the temperature, which increases the NOx and CO near the entrance, but gradually towards the outlet of the combustion chamber. The energy absorbed by H2O leads to a severe decrease in temperature and subsequent reduction in the amount of NOx and CO emissions. With increasing H2O diluent, changes in temperature are not very significant, while changes in pollutants CO and especially NOx, are remarkable. With the increase of H2O diluent, the maximum amount of CO emission displaces towards the inlet of the combustion chamber. However, it should be noted that, at a specific value of H2O diluent, the length of the combustion chamber should not be less than critical value, causing the exhaust of the pollutant with large volume to the environment. After the critical point, the increase in the length of the chamber has little effect on reduction of the pollutant exhaust. However, by increasing the H2O diluent, enclosures with smaller length can be utilized. (C) 2019 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.