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Detonation Initiation, Propagation, and Suppression


Understanding the fundamental processes of detonation is essential for both energy and safety issues. The rapid energy conversion characteristic of detonation is significantly useful in industrial and military applications, such as detonation engines and high explosives. On the other side, this characteristic of detonation is not preferred in the field of safety engineering. Detonations with violent pressure waves frequently cause catastrophic human casualties and property damages.

This dissertation presents theoretical and numerical studies on detonation initiation, propagation, and suppression. Multiple numerical tools are employed to study detonation phenomena: a toolbox to calculate the steady state homogeneous detonation properties, a simplified unsteady compressible solver for Lagrangian equations to simulate detonation behaviors as a primary stage, and a compressible multi-component reacting flow solver to perform transient simulations of the detonation phenomena in detail.

Several methods to predict the occurrence of detonation initiation and deflagration to detonation transition are developed. Transient and integral reactivity gradient methods are proposed and evaluated on the basis of the Zel'dovich gradient theory. Prediction models of detonation initiation developed from machine learning techniques are also presented. Potential applications of statistical learning models with the conventional numerical simulations are discussed.

Effects of fuel-stratification on detonation propagation are identified by detailed numerical simulations. Both the leading shock pressure and detonation propagation speed in the fuel-stratified layer are compared to the corresponding homogeneous Chapman-Jouguet detonation properties. The shock reflection and transmission theory, and the Zel'dovich-Neumann-Döring detonation structure model are employed to describe deficits or surpluses in properties of stratified detonation. The overall mechanism of stratified detonation propagations is also proposed.

Detonation suppression in water vapor concentration gradients is investigated by the transient numerical simulations with various water vapor concentrations and thicknesses of the gradient layer. From the simulations, three combustion modes are observed: 1) normal detonation propagation, 2) detonation mitigation and re-initiation, 3) detonation suppression. The separation of leading shock and reaction front is the main cause of a detonation suppression. A regime map for limits of each mode is introduced showing that the mode depends on the normalized ignition delay time including shock reflection effect and the ratio of the gradient layer thickness to the detonation induction length. The transient reactivity gradient is employed to understand the detonation re-initiation process after the mitigation of the initial detonation.

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