The influence of amines on the combustion of n-heptane

Abstract

Studies have been made of the influence of a variety of amines on the spontaneous ignition of mixtures of n-heptane and air (1:10). Pressure/temperature ignition profiles have been constructed for the following additives (1%): mono-, di-, and trimethylamine, mono-, di-, and triethylamine, aniline, N-methylaniline and N,N-dimethylaniline. Each profile showed two distinct lobes (L1 and L2) at the cool-flame/two-stage ignition boundary. The mode of action of these additives is explained in terms of their effect on the mechanisms of hydrocarbon combustion known to be operative in these lobes. The ability of the amines to retard cool-flame propagation is correlated with the nature and extent of their alkyl and aryl group substitution and with their initial partial pressures. A critical concentration of added amine is reached, above which the pressure change accompanying the cool flame, Δpcf is unaffected and a second, greater critical concentration is reached above which the induction period of the first cool flame becomes infinite and only slow combustion ensues. Evidence is presented which shows that some species which lead to the second stage of two-stage ignition are formed during the passage of the cool flame and not prior to it. Finally, the work shows that the second stage of two-stage ignition is controlled by the magnitude of the first cool flame as measured by the accompanying pressure pulse and thus provides support for the view that the principal chain-propagating steps in the combustion of fairly high molecular weight hydrocarbons at low pressures are the same as those operating at higher pressures.