Abstract
Evolution of the spontaneous ignition of n-butane is investigated under conditions of varying heat dissipation rates, controlled through the intensity of gas motion generated during mechanical compression of the reactants in a cylinder. As the heat dissipation rate is enhanced the minimum compressed gas temperature required for ignition is also raised, from 700 to 870 K in the present conditions. This increase is linked to the initial rate of cooling in the post compression period before significant chemical heat release begins to take place. At this threshold for reaction the common factor is the prevailing gas temperature, which at its minimum during a marginally supercritical ignition delay, is about 600 K. Heat release rates just balance dissipation rates here, permitting the evolution of “low temperature” degenerate chain branching. Moreover, the end-of-compression temperatures within which an inverse temperature dependence of the ignition delay is observed increase when the heat dissipation rate is raised. This feature is also rationalised in terms of the prevailing post-compression gas temperature, consistently in the range 660–725 K. The heat release rates derived from experimental results exhibit a negative temperature coefficient in this range and are the origin of the complex, overall time dependence. Some contrasts due to the much lower reactivity of isobutane are also presented.
Published Version
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