Experimental Testing of a 3 Inch Rotating Detonation Engine With Air and Hydrogen

This work presents the experimental characterization of a small-scale, air-breathing rotating detonation engine (SABR) operating with gaseous hydrogen and atmospheric air. The test article consists of a 3-inch annular combustor with a 0.2-inch gap width, a 2.378-inch channel height, and an integrated converging–diverging aerospike nozzle with an expansion-optimized cowl. The engine was tested over total mass flux values from 185 to 255 kg/m^2-s and equivalence ratios from 1.4 to 2.0. A modular plate-stacked design was used to simplify fabrication and allow future injector and geometry modifications. Thrust measurements were collected using a calibrated load-cell thrust stand, and injector plenum pressures were monitored throughout each test. Across the explored operating space, the engine ignited reliably and produced repeatable thrust in a deflagration-dominated regime, but no clear signatures of rotating detonation were observed in the thrust histories or high-speed exhaust imaging. These initial results establish a baseline deflagration-mode performance for the SABR engine and highlight the need for expanded testing with high-frequency chamber pressure measurements, refined injector and annulus designs, and operation at higher chamber pressures to determine whether stable rotating detonation can be achieved in this configuration.