An experimental and kinetic modeling study of the two stage autoignition kinetic behavior of C7, C10, C12, and C14 n-alkanes

摘要

The oxidation of mixtures of n-heptane, n-dodecane, and n-tetradecane with oxygen and nitrogen at stoichiometric conditions of 0.3 mole% carbon fuel is studied in the Princeton Variable Pressure Flow Reactor at temperatures of 500-1000 K and at a pressure of 8 atm. The overall.oxidative reactivity for these three n-alkane fuels was compared in detail over the low temperature, negative temperature coefficient, and hot ignition regimes. Comparing their relative reactivities it was observed that n-heptane had the lowest activity in the low temperature regime. In the hot ignition regime, the behavior of all three fuels was almost indistinguishable. For carbon numbers above C_(12), there is essentially no difference in the experimen ally observed reactivity with carbon number in any regime for stoichiometric mixtures having the same carbon content The predictions using available chemical kinetic models for the oxidation of the family of large carbon number n-alkanes are compared against each other and experimental results. Only the model by Sarathy et al. was able to capture qualitatively the relative reactivity behavior of all three fuels over the entire temperature domain considered. Detailed analysis of the modeling results revealed large differences in the mechanistic details of these models especially in the low temperature kinetic regime. Very different pools of intermediate stable species and radicals arepredicted by the different models.