Nonpremixed ignition of C₇-C₁₆ normal alkanes in stagnating liquid pool

The nonpremixed ignition temperatures of n-decane, n-dodecane, and n-hexadecane were measured in a liquid pool by heated stagnating oxidizing flow at atmospheric pressure. Together with previous results on n-heptane, it is shown that, for the C₇-C₁₆ n-alkanes, the nonpremixed ignition temperature increases monotonically with increasing carbon number, and as such is contrary to the behavior of homogeneous ignition delays. Numerical simulation of the ignition events for n-heptane, n-decane and n-dodecane, employing a recently developed high temperature kinetic model, showed good agreement with the experimental results both qualitatively and quantitatively. Sensitivity and computational analyses indicate that the reason for the higher ignition temperature with increasing fuel molecular size is mostly due to their progressively reduced diffusivity, which leads to correspondingly reduced fuel concentration in the ignition kernel.