A Turbineless Hybrid Electric-Hydrogen Propulsion System with On-Demand Aluminum-Water Hydrogen Generation: Design and Static Thrust Characterization

In this paper a turbineless hybrid electric-hydrogen propulsion system was built and tested under static conditions. Two electric ducted fans (EDFs) supplied the baseline thrust and combustion airflow. An alkaline aluminum-water reactor generated hydrogen on demand for combustion downstream of the fans. Rod immersion depth controlled hydrogen production, which was measured at each condition with a hydrogen-calibrated mass-flow meter. Aluminum consumption was also measured to determine the effective hydrogen yield. Tests covered ten immersion depths, with 76 independent paired EDF-only and hybrid runs per condition. At the highest hydrogen flow, thrust rose from 8.49 ± 0.15 to 9.94 ± 0.21 N, an increase of 17.1%. Hydrogen production increased approximately linearly with exposed aluminum area (R² = 0.997), while the marginal thrust gain decreased. The momentum-based combustion-to-jet conversion indicator ranged from 7.3 to 9.1% and was highest at intermediate hydrogen flows. Chamber pressure and fan supply power were measured in a separate session with paired runs without and with combustion. Measured thrust was 1.7 to 3.5% below the ideal nozzle prediction from chamber pressure. Combustion increased fan supply power from 1.49 kW to between 1.60 and 2.02 kW. As hydrogen flow increased, jet kinetic power fell from 40% to 19% of the combined electrical and hydrogen chemical exergy input.