Detonation diffraction in a multi-step channel

Abstract

This research investigated multiple detonation diffraction events in order to better understand the limits and benefits of diffraction strategies with respect to pulse detonation engine design. Hydrogen/air detonations were generated using swept ramp obstacles in a 1.27 m long channel with a cross section of 25.4 mm by 88.9 mm and were diffracted into various multiple-stepped openings. This allowed the detonation wave diffraction transmission limits to be determined for hydrogen/air mixtures and to better understand reinitiating mechanisms throughout the diffraction process. Tests were conducted for area ratios ranging from 2.00-2.60 with varying equivalence ratios from 0.5-1.5. Computational methods were used to better understand the diffraction phenomenon using a series of sensitivity studies for different chemistry sets, computational cell size and equivalence ratio. Experimental tests used combined optical shadowgraph and particle image velocimetry imaging systems to provide shock wave detail and velocity information. The images were observed through a newly designed explosive proof optical section and split flow detonation channel. It was found that area ratios of 2.0 could survive single and double diffraction events over a range an equivalence ratio range of 0.8 to 1.14 Area ratios of 2.3 survived the primary diffraction event for equivalence ratios near stoichiometric for the given step length. Detonation diffraction for area ratios of 2.6 did not survive the primary diffraction event for any equivalence ratio and were unable to transmit to a larger combustor.