Ethylene Ignition and Detonation Chemistry, Part 2: Ignition Histories and Reduced Mechanisms

The detailed mechanism of 148 steps among 34 chemical species that has been described previously is reduced through steady-state and partial-equilibrium approximations to achieve simplified descriptions for use in ignition and detonation studies. The concentration histories for ethylene oxidation reveal different types of ignition processes under not very different conditions of pressure and temperature. When unimportant steps are sequentially deleted from the detailed mechanism, a short mechanism is developed involving only 38 irreversible elementary steps among 21 chemical species. This short mechanism is designed to be applied with reasonable accuracy over the entire range of conditions indicated previously. If attention is restricted to the induction period, then these 38 steps can be decreased to 21. During induction, the important chain carriers are mainly H, O, OH, and C 2 H 3 above 1500 K, whereas C 2 H 3 , HO 2 , and H 2 O 2 become dominant carriers below this temperature. At high temperatures, expressions for ignition time are derived by using radical depletion as the ignition criterion, whereas at lower temperatures, simplified thermal explosion theory in principle can be applied. Based on the detailed mechanism, a two-step mechanism involving only seven species is developed, which can facilitate computational investigations of multidimensional ignition and detonation processes of ethylene-air mixtures.