Role of overdriven state of ignition wave in pre-detonators on detonation transition modes in a flat chamber

Using the small-diameter pre-detonator is an important method to provide reliable and fast detonation to the denotation engines (i.e., pulse detonation engines or rotating detonation engines). This work examines the role of the overdriven state of ignition waves generated in pre-detonators on detonation transition modes in a flat chamber. For this purpose, a series of experiments are performed using different lengths of pre-detonators (L_p) with different mixtures to initiate the detonation in the main chamber. Results show that maintaining an overdriven state at the pre-detonator exit can significantly enhance the probability of fast detonation initiation (i.e., supercritical/critical mode) in the main chamber. Especially for the high nitrogen diluting ratio (β) mixtures, forming the overdriven detonation at the pre-detonator exit becomes a necessary condition for the fast initiation. As a result, the fast detonation initiation mode distributes in an upper-right shrinking ‘canyon’ in the L_p-β map. It is illustrated that the increased overdriven degree required for transitioning detonation wave under the higher β cases is responsible for this observation.