Ignition of non-premixed C3–C12 n-alkane flames

Ignition temperatures of non-premixed C3 and C5–C12 n-alkane flames were determined in the counterflow configuration at atmospheric pressure, a free-stream fuel/N2 mixture temperature of 448 K, a local strain rate of 140 s−1, and fuel mole fractions ranging from 1% to 12% in the fuel stream. The strain rate was measured on the fuel side using Laser Doppler Velocimetry. Simulations of the experiments were performed using the recently developed JetSurF 1.0 reaction model consisting of 194 species and 1459 reactions. In both experiments and simulations, the ignition temperatures of all n-alkane flames were found to decrease with increasing fuel concentration. The computed ignition temperatures are in close agreement with the experimental data for all C5–C12 n-alkanes, while for propane flames the data are slightly over-predicted. Detailed sensitivity analyses on both reaction rates and binary diffusion coefficients were performed, and the ignition temperature was determined to be sensitive both to fuel diffusion and the H2/CO and small hydrocarbon kinetics. The dependence of the ignition temperature on the fuel molecular weight was determined to differ at low and high fuel mole fractions, due to the competition between the fuel reactivity and diffusive transport.