The role and rate of hydrogen peroxide decomposition during hydrocarbon two-stage autoignition

The role of hydrogen peroxide during the development of two-stage ignition of alkanes is discussed in propane combustion using a reduced kinetic model comprising 58 species in 344 irreversible reactions. Numerical simulations of two-stage and multiple-stage ignitions of propane + oxygen in a closed vessel, and two-stage ignition in a rapid compression machine are made. The model is validated by a construction of the closed vessel p-T-a ignition diagram and comparing it with published experimental results. A detailed analysis, using temperature/composition versus time and phase-plane [H2O2]-T plots, is made to show regions of kinetic sensitivity leading to ignition. Rate of production and sensitivity analyses are used to determine the most important reactions contributing to the formation of hydrogen peroxide as an intermediate, and to the heat release rate eventually culminating in the second stage of two-stage ignition. The most important (but not exclusive) sequence of reactions leading to HO2 formation is identified to be through formaldehyde as a molecular intermediate, it being formed predominantly from methyl radical oxidation. This seems not to have been previously recognized. The relationship to other sources of HO2 is investigated, and the effect of change in temperature, pressure, and composition on the kinetics is discussed. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.