Predictions of soot formation in burner-stabilized stagnation flames using various reaction mechanisms

To clarify the effects of reaction mechanisms on soot formation, a two-dimensional numerical simulation was performed for a burner-stabilized stagnation flame. The GRI-3.0, Appel-Bockhorn-Frenklach (ABF), and DLR models were employed as representative reaction mechanisms. The soot particle formation model was a two-equation model, and only acetylene was assumed to be the soot-nucleating species. The ambient pressure and inlet temperature were 0.1 MPa and 473 K, respectively, and the distance between the burner surface and the stagnation plate (H_p) varied from 5.5 to 12 mm. The simulation was conducted using OpenFOAM, and the results were validated with experimental data based on the temperature distribution and soot volume fraction at H_p. After soot nucleation began, the number density became large in the preheating zone. As the soot transported downstream, coagulation and surface growth accelerated, and the mass density became large. Furthermore, while the effect of the reaction mechanism on temperature distribution was small, the effect on the soot growth rate was large. In the preheating zone, the DLR model showed the largest nucleation rate, which could be due to the abundant acetylene formation reaction. At the downstream, the DLR model showed the smallest nucleation rate, which is probably because many acetylene consumption reactions were included in the DLR model. As a result, the soot volume fraction of the DLR model at H_p was smaller than that of the GRI-3.0 and ABF models. These results suggest that the reaction mechanism, especially the fuel-pyrolysis sub-mechanism, has a significant impact on the prediction of soot formation.