Autoignition theory

The first attempts to understand quantitatively the high-temperature chemical processes were related to combustion. They took place in the first part of the last century, partly with the development of thermal theories and theories for chain reactions and partly with work on high-temperature oxidation of hydrocarbons (to understand flame propagation) and low-temperature oxidation (to understand autoignition and knock in internal combustion engines). 

Recent theories of knock (4, 33, 45, 207) have emphasized the role played by the hydroperoxy radical (H02-) under incipient knock conditions. H02 radicals would be formed by Reactions 9", 11, and 9-4. Reaction 9, with an activation energy of 40 kcal. (204), might be the reaction required to trigger ignition. The yields of both hydrogen peroxide (207) and hydrogen (107) have in fact been observed to increase rapidly near autoignition. 

Inhomogeneities, however caused, can be amplified by pre-ignition reaction. The conditions under which they can give rise to autoignition centres and hot spots have been examined in terms of turbulent structure and simple thermal explosion theory. Bradley [180] assumed the size of an autoignition centre to have the spatial scale of temperature inhomogeneities, distributed about the integral thermal scale of the gas dynamic turbulence. These distributed sizes were compared with computed critical sizes for thermal explosion, for different values of chemical parameters in... 

The relationships established above have more qualitative than quantitative value. The empirical kinetic law (150) in particular should be replaced by a globalized or detailed reaction mechanism. This would be part of the framework of the unified theory of autoignitions, which takes into account both the interaction between the branching and the degenerate branching mechanisms and the thermal phenomena. Such models can only be treated by numerical methods. 

Theory. A broadband Nitrogen-15 NMR study of nitrocellulose (NC) as a function of temperature was conducted in an attempt to investigate the dynamics of the polymer chains. This approach is justified by the assumption that an understanding of the onset of motion is prerequisite to fundamental understanding of any mechanism of degradation and autoignition. 

---