On radical-induced ignition in combustion systems

This article reviews recent theoretical developments on incipient ignition induced by radical runaway in systems described by detailed chemistry. Employing eigenvalue analysis, we first analyze the canonical explosion limits of mixtures of hydrogen and oxygen, yielding explicit criteria that well reproduce their characteristic Z-shaped response in the pressure-temperature plot. Subsequently, we evaluate the role of hydrogen addition to the explosion limits of mixtures of oxygen with either carbon monoxide or methane, demonstrating and quantifying its strong catalytic effect, especially for the carbon monoxide cases. We then discuss the role of low-temperature chemistry in the autoignition of large hydrocarbon fuels, with emphasis on the first-stage ignition delay and the associated negative-temperature coefficient phenomena. Finally, we extend the analysis to problems of nonhomogeneous ignition in the presence of convective-diffusive transport, using counterflow as an example, demonstrating the canonical similarity between homogeneous and nonhomogeneous systems. We conclude with suggestions for potential directions for future research.