Numerical study of soot formation in laminar coflow methane/air diffusion flames doped by n-heptane/toluene and iso-octane/toluene blends

The laminar coflow nitrogen-diluted methane/air diffusion flames doped with a small amount of n-heptane/toluene and iso-octane/toluene binary mixtures, investigated experimentally by Kashif et al. (2015), were simulated numerically by using a detailed reaction mechanism and a sectional polycyclic aromatic hydrocarbon (PAH)-based soot model. The numerical model provides results in reasonable qualitative agreement with the experimental data by using the same chemical mechanism, the same soot model, and the same set of constants employed successfully in a previous study to model the effects of n-heptane/iso-octane doping, demonstrating that this overall model is promising to model soot formation in gasoline flames. Soot production is enhanced monotonically with increasing the toluene content in either the n-heptane/toluene or iso-octane/toluene doping fuel mixture. The increase in benzene and pyrene production displays a non-monotonic and synergistic response to the increase in toluene content. These numerical results are consistent with available experimental results as far as the trends in the effects of increasing the toluene content are concerned. Model results show that the dominant pathways responsible for the synergistic effects on benzene and pyrene production are respectively C6H5CH3 (toluene) + H ↔ A1 (benzene) + CH3 and A3- (C14H9) + C2H2 ↔ A4 (pyrene) + H.