A theoretical analysis of the first-stage ignition delay in hydrocarbon oxidation chemistry

Extending the pioneering work of Peters and co-workers on the first-stage ignition delay of n-heptane/air mixtures, the ignition delay is first calculated using the LLNL detailed mechanism, which is then further reduced for analysis of the first-stage ignition at low- and intermediate-temperature conditions. Results show that the first-stage ignition is dominated by the competition of low-temperature branching and termination, with chain-branching being the isomerization reactions as well as the keto-hydroperoxide decomposition. As temperature increases to the intermediate range, the termination pathways result in a minimum in the delay, the state of which is theoretically derived. Simple analytical solutions for the delay as well as the radical evolutions are presented to identify the rate constants that control the first-stage ignition and quantify the influence of mixture composition, initial temperature and pressure.