Computational Singular Perturbation Analysis of n-Heptane Two-Stage Ignition

摘要

Two-stage ignition (and related cool flame and negative temperature coefficient (NTC) phenomena) during low-temperature oxidation of large hydrocarbon molecules is a well-established process. Initial phenomenological interpretations of these phenomena date back to 1940-50s. Benson has proposed a comprehensive mechanistic analysis in terms of specific elementary processes. Among the major points of his analysis, Benson suggested that (1) competition between the highly reversible oxygen addition reaction R+O_2 reversibleRO_2 and the reaction R+O_2 → olefin+HO_2 (where R represents an alkyl radical) provides the switch from branching to non-branching behavior as temperature increases and (2) for large hydrocarbon molecules, the low-temperature branching sequence proceeds via internal isomerizations (Fig. 1). Detailed reaction mechanisms of various levels of predictive ability describing low-temperature oxidation of large hydrocarbons started to appear in late 1980s and are still under heavy development at present. In spite of the availability of detailed reaction schemes capable of quantitative predictions of various experimental observations related to two-stage ignition phenomena, the detailed and unambiguous interpretation of these model predictions is still controversial. This is primarily due to the complexity of the observed kinetic behavior as well as to the large size of the resulting detailed models which makes them difficult to interpret using conventional chemical kinetics tools (i.e, flux/sensitivity analysis).