Pulse Detonation Rocket Magnetohydrodynamic Power Experiment

The production of onboard electrical power by pulse detonation engines is problematic in that they generate no shaft power; however, pulse detonation-driven magnetohydrodynamic (MHD) electrical power generation represents one intriguing possibility for attaining self-sustained engine operation and generating large quantities of burst power for onboard electrical systems. To examine this possibility further, a simple heat-sink apparatus was developed for experimentally investigating pulse detonation-driven MHD generator concepts. The hydrogen-oxygen-fired driver was a 90-cm-long stainless steel tube having a 4.5-cm square internal cross section and a short Schelkin spiral near the head-end to promote rapid formation of a detonation wave. The tube was intermittently filled to atmospheric pressure and seeded with a CsOH/methanol spray prior to ignition by electrical spark. The driver exhausted through an aluminum nozzle having an area contraction ratio of A*/Ac=1/10 and an area expansion ratio of Ae/A*=3.2 (as limited by available magnet bore size). The nozzle exhausted through a 24-electrode segmented Faraday channel (30.5-cm active length), which was inserted into a 0.6-T permanent magnet assembly. Initial experiments verified proper drive operation with and without the nozzle attachment, and head-end pressure and time-resolved thrust measurements were acquired. The exhaust jet from the nozzle was interrogated using a polychromatic microwave interferometer yielding an electron number density on the order of 1012 cm–3 at the generator entrance. In this case, MHD power generation experiments suffered from severe near-electrode voltage drops and low MHD interaction; i.e., low flow velocity, due to an inherent physical constraint on expansion with the available magnet. Increased scaling, improved seeding techniques, higher magnetic fields, and higher expansion ratios are expected to greatly improve performance.