Laminar flame speeds and extinction stretch rates of selected aromatic hydrocarbons

The laminar flame speeds and premixed extinction limits of n-propylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and toluene have been studied experimentally to assess the effects of different alkyl substitutions to the benzene ring on flame propagation and extinction. The experiments were carried out in a twin-flame counterflow setup under atmospheric pressure. The laminar flame speeds of fuel/air mixtures at two unburned mixture temperatures of 400 K and 470 K were determined over an equivalence ratio range of φ = 0.7-1.4. Additionally, the extinction stretch rates of fuel/O ₂/N ₂ mixtures at an unburned mixture temperature of 400 K were measured over an equivalence ratio range of φ = 0.8-1.6, with an oxidizer composition of 16% O ₂ and 84% N ₂ by mole. The experimental laminar flame speeds and extinction stretch rate values were compared to simulated results, for each fuel, using detailed kinetic models available in the literature. The simulation results were found to be in reasonable agreement with the current experimental data, except for 1,2,4-trimethylbenzene, where the model under-predicts the extinction limits significantly. Sensitivity and flux analyses were conducted to identify reactions and species to which the computed results were most sensitive.