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Abstract
The pollutants produced by the burning of fossil fuels have a severe impact on the environment and on mankind. Computational fluid dynamics (CFD) is a powerful tool, which is widely used to predict the emission of these pollutants from industrial combustion systems. Nevertheless, to predict these emissions the chemical reaction must be represented by a detailed mechanism, which includes pollutant formation pathways. Thus, using a complex mechanism, especially in 3D simulations with a realistic geometry is prohibitively expensive computationally. In this article, the equivalent reaction networks (ERN) method is used in conjunction with a Reynolds-averaged Navier Stokes (RANS) approach to reduce the cost of these computations. For this purpose, a pilot stabilized stoichiometric methane-air flame is chosen with a specific interest in species with slow time scales, such as CO and NOx. The Favre averaged CFD results are then compared to previously-reported experimental measurements and earlier computations using conditional moment closure (CMC) at five axial locations within the flame. Despite the simplicity of the ERN method in contrast with other more complex combustion models, the comparison of the CFD results with the experimental measurements for the prediction of CO are extremely encouraging.
NOMENCLATURE
| c | = | progress variable |
| hk | = | absolute enthalpy |
| hs | = | sensible enthalpy |
| k | = | species index |
| = | molecular diffusivity | |
| = | Favre averaged turbulent kinetic energy | |
| = | mass flow rate passing into the reactor from inlet i | |
| M | = | total mass |
| Mk | = | mass of species k |
| = | Favre PDF of c | |
| = | unstrained planar laminar flame speed | |
| Sc | = | Schmidt number |
| T | = | temperature |
| Tb | = | burned mixture temperature |
| Tu | = | unburned mixture temperature |
| u | = | axial velocity |
| U | = | internal energy |
| V | = | volume of control volume |
| = | molecular weight of species k | |
| x | = | direction of the flow |
| Y | = | mass fraction |
| Z | = | mixture fraction |
Greek Symbols
| = | laminar flame thermal thickness | |
| = | Kolmogorov length scale | |
| Λ | = | integral length scale |
| = | Favre averaged turbulent dissipation rate | |
| vu | = | kinematic viscosity of unburned mixture |
| ρ | = | density of mixture |
| = | equivalence ratio | |
| = | mean reaction rate of species k | |
| = | volumetric reaction rate of species k |