Studies have been made of the spontaneous ignition of
n
-heptane+oxygen+inert gas mixtures at temperatures from 440 to 650°C, where ignition takes place by a one-stage process and no cool flames are observed. Detailed measurements have been made of the variation of minimum ignition pressure with such factors as the temperature, the composition of the mixture undergoing ignition and the nature, shape and extent of the surface of the reaction vessel. In particular, experiments in a wide variety of vessels show that the surface parameter which primarily determines the ignition tendency is the average distance of the molecules from the walls, rather than the surface:volume ratio. The quantitative relations observed experimentally are compared with the predictions of two isothermal chain-branching mechanisms involving distinct chemical paths and with the consequences of the theory of thermal ignition. It is shown that the results in small vessels (volume < 500 cm
3
) are best explained in terms of an isothermal chain mechanism involving hydrogen peroxide as degenerate-branching agent, although in larger vessels thermal factors probably become increasingly important.
Supplementary material to "On the similarities and differences between the products of oxidation
of hydrocarbons under simulated atmospheric conditions and cool-flames"
