Effect of non-thermal product energy distributions on ketohydroperoxide decomposition kinetics

• Published in: Proceedings of the Combustion Institute 2015, Vol.35 (1), p.283-290
• Main Authors: Goldsmith, C. Franklin, Burke, Michael P., Georgievskii, Yuri, Klippenstein, Stephen J.
• Format: Article
• Language: English
• Subjects: Channels; Combustion; Computer simulation; Decomposition; Direct dynamics; Energy distribution; Inclusions; Internal energy; Low-temperature ignition; Master equation; Mathematical analysis; Networks; Non-Boltzmann effects; Propane oxidation
• ISSN: 1540-7489; 1873-2704
• DOI: 10.1016/j.proci.2014.05.006

The decomposition of ketohydroperoxides (OQ′OOH) to two radicals is commonly predicted to be the key chain branching step in low-temperature combustion. The possibility of a direct decomposition of the OQ′OOH from its initially produced energy distribution is studied with a combination of master equation (ME) and direct trajectory simulations. The temperature and pressure dependent rate constants for the thermal decomposition of a ketohydroperoxide, HOOCH2CH2CHO, to four product channels were computed using RRKM/ME methods. Direct dynamics calculations were initiated from a transition state in the O2+QOOH reaction network to understand the fraction of energy in that transition state that is converted into the internal energy of the OQ′OOH. A novel approach to solving the master equation is used to determine the probability that a vibrationally hot OQ′OOH either will be stabilized to a thermal distribution or will react to form new products. Under most conditions, the majority of vibrationally excited OQ′OOH will be quenched into a thermal distribution. At higher internal energies and lower pressures, however, a significant fraction of the hot OQ′OOH will decompose rather than thermalize. Proper interpretation of low-pressure experiments may require inclusion of vibrationally hot intermediates, particularly if a chemical kinetic mechanism is optimized against the low-pressure data.