B. Thermokinetic oscillations. Thermokinetic oscillations accompanying propane oxidation

Abstract

Gaseous hydrocarbon oxidations are often accompanied by remarkable non-isothermal phenomena, such as oscillatory cool flames and complex ignitions. These owe their existence to an interplay between kinetics and self-heating via thermal feedback in a system involving chain branching. The present work illustrates these phenomena and provides a quantitative assessment of thermokinetic concepts applied to them.

Propane is oxidised in a stirred closed reactor. Characteristically, time-dependent oscillations occur in the pressure range 40–100 kN m^–2 at vessel temperatures between 570 and 660 K. Substantial temperature changes accompany the oscillating reaction rate, and these changes are measured by a fine (25 µm) thermocouple and rapid recording equipment. Oscillating temperatures may vary in form from roughly sinusoidal with damping, to steep cusp-like maxima of hardly diminished amplitude, multiple events being terminated abruptly by the consumption of fuel.

Thermokinetic oscillations depend vitally on thermal feedback and hence on heat transfer: by the deliberate variation of heat transfer properties such as heat capacities and thermal conductivities (with diluting gases), and intensities of stirring, we are able to test this dependence.