Reaction of nitrogen dioxide with hydrocarbons and its influence on spontaneous ignition. A computational study

Estimates are made, by using BHandHLYP/6-311G** density functional molecula r orbital theory, of the activation energies and frequency factors for the reaction of NO2 with methane, ethane, propane, isobutane, and benzene. For the aliphatic hydrocarbons, over the temperature range 600-1100 K, the rate of formation of a new isomer of nitrous acid, HNO2, is very similar to tha t for the formation of the common isomer, HONO. This complicates our descri ption of the acceleration of spontaneous ignition of diesel fuels by organi c nitrates. These rate data are used in a reduced kinetic model to examine the effect of NO2 upon the spontaneous ignition of some linear- and branche d-chain aliphatic hydrocarbons. It is concluded that, under typical diesel engine operating conditions, the spontaneous ignition of linear-chain paraf fins is accelerated by the presence of NO2, but may be retarded for heavily branched-chain isomers. An Appendix discusses the relative importance of t unnelling in hydrogen-transfer reactions.