The advent of detonation-based propulsion systems represents an opportunity for more sustainable combustion processes and hypersonic travel. In regular detonations, some yet to be resolved instabilities are attributed to the propagation and collision of triple points, formed at the intersection of a Mach stem, an incident shock and a transverse wave. Over time, the tracks observed by these points form a structure made of diamond-shaped cells. Ultimately, The ability to sustain these instabilities plays a key role in the propagation of detonations. The present work unveils the dynamics of gaseous detonations at a sub-cellular level. The experiments are conducted with hydrogen fuel which is of great potential for detonation engine applications. The hydrogen-oxygen mixtures are held at stoichiometry and the nitrogen dilution in oxygen is varied from 30% to 70%. This allows to observe the effects of activation energy through the dilution on the sub-cellular wave dynamics. Measurements of cell sizes and wave velocity are reported through shadowgraph imaging. A new methodology is developed for the simultaneous resolution of the velocity field and cellular structure. The statistical analysis is made possible due to the design of a fully automated detonation facility. The experiments are conducted in a thin channel to minimize gradients in the third direction and confine the detonation cells to a plane. The results in cell sizes are in good agreement with the literature and expand the conditions reported thus far. Local observations of the velocity within the cells are used to explain the regularity of the overall wave speed, found to increase at lower dilution. Lastly, high fidelity simulations are conducted to model the cellular structure in hydrogen-air oblique detonation waves. Similarly to the experiments, the velocity field is extracted along the detonation cells and reveals the effects of wave curvature on triple point dynamics.

Detonation-based propulsion systems are known for their high efficiency and energy release when compared to deflagrative systems, making them an ideal candidate in hypersonic propulsion applications. One such engine is the Oblique Detonation Wave (ODW) engine, which has a similar architecture to traditional scramjets but shortens the combustor and isolator to an anchored ODW after fuel injection. Previous research has focused on using a two-dimensional wedge to induce an ODW while limiting total losses through the combustor. In this configuration, a two-dimensional wedge-based architecture entails a rectangular duct, limiting potential inlet design and increasing overall skin friction. However, an inward-turning axisymmetric ODW wedge architecture, where a two-dimensional wedge is revolved around a central axis, has yet to be examined in detail. The work at present aims to investigate the fundamental physics required to predict the Oblique Shock Wave (OSW) for an inward-turning axisymmetric flow, which is critical for designing a circular ODW engine combustor. Multiple steady simulations of inviscid and ideal air at Mach 4, 6, and 8 were performed over a 1-inch wedge with wedge angles of 16°, 18°, and 20°. The radius of the inlet boundary was also varied between 1, 3, and 5 inches to examine the effect of increasing the blockage ratio. The results showed that the shock angle for an inward-turning axisymmetric flow was up to 8% steeper than the analytical, two-dimensional wedge solution. Additionally, it was found that the OSW diverged further from the two-dimensional solution when the blockage ratio was increased. These findings provide insight into the flow physics that must be considered when designing inward-turning axisymmetric ODW engines.