Fuel-oxygen mixing and detonation propagation in a linear rotating detonation rocket engine geometry

Experiments were performed in a non-premixed linear Rotating Detonation Engine combustion channel in which hydrogen and oxygen was injected into room temperature argon. The hydrogen and oxygen were injected into the channel via two parallel plenums, each with linear arrays of ninety-four, 1.3 mm diameter holes, axially spaced 4.8 mm center-to-center. A Chapman-Jouguet (CJ) detonation was initiated in a driver section, and transmitted into the optically accessible test section where the hydrogen-oxygen layer was generated. Channel widths of 12, 10 and 8 mm were tested. For the 12 mm channel width, schlieren video showed unsteady detonation propagation and detonation cell structure was only recorded on a soot foil placed on the hydrogeninjection side of the channel. This asymmetry in cell structure was attributed to the high momentum oxygen jet deflecting the hydrogen jets. Decreasing the channel width to 8 mm produced a symmetric, steady detonation wave that travelled at an average velocity of 2140 m/s, i.e., 25 % below the theoretical CJ detonation velocity for undiluted stoichiometric hydrogen-oxygen. The velocity deficit was primarily attributed to argon-dilution of the hydrogen oxygen mixture. The results imply that the 50 % CJ detonation velocity deficits commonly observed in operating hot RDEs can be attributed to preburning of the injected fuel-oxygen that is not present in the experiment.