Aluminum Fuel for Underwater Vehicles
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jeldres-fjeldres-sm-sdm-2026-thesis.pdf
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9.92 MB
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Author(s)
Jeldres Neira, Francisco J.
Advisor(s)
Hart, Douglas P.
Date Issued
February 2026
Publisher
Massachusetts Institute of Technology
Abstract
Buoyancy engines are a key piece of profiling floats, ocean gliders, and certain Autonomous Underwater Vehicles (AUVs), enabling long-endurance ocean sensing and monitoring. However, conventional buoyancy systems—typically based on oil-pumped volume change and battery-powered actuation—remain limited by their low energy density, high mechanical complexity, and the need for large pressure-resistant housings. This thesis investigates the underlying mechanisms of aluminum-water reactions in specific aqueous solutions, exploring improved gas generation capacity, reaction-onset reduction, and rate enhancement. It applies these insights to the design of a novel aluminum-fueled buoyancy engine for underwater platforms.
The work analyzes the chemistry and thermodynamics of aluminum-water reactions primarily using aqueous ammonia, which exhibits a dual function, serving simultaneously as the solvent and as a gas promoter. This combined role facilitates greater potential energy generation per unit volume of solvent, an essential characteristic for compact, high-energy-density applications such as underwater systems. Additionally, the main effects of incorporating hydrochloric acid, hydrogen peroxide, and their mixtures with aqueous ammonia as solvents for aluminum-water reactions are investigated. It is demonstrated that hydrochloric acid significantly enhances both the gas generation capacity and the disruption of the passivating aluminum oxide layer, while hydrogen peroxide fundamentally accelerates the reaction onset; consequently, fine-tuned mixtures utilizing aqueous ammonia as the baseline can be rationally designed to optimize the performance characteristics of each chemical activator.
The study then compares dry and flooded buoyancy-engine architectures, identifying key trade-offs in structural design, pressure management, energy density, and system integration. A flooded configuration is developed in detail: the entire engine operates at ambient ocean pressure, eliminating the need for a pressure hull and enabling the use of extremely small, low-power pumps. The analysis shows that the majority of the energy required for buoyancy changes is supplied directly by the aluminum fuel, rendering electrical consumption nearly negligible and significantly extending mission duration.
Overall, this thesis advances both the fundamental understanding of aluminum-water reaction chemistry with specific solvents and the system-level design principles needed to translate this technology into a practical buoyancy engine for next-generation, long-range ocean exploration and monitoring systems.
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
System Design and Management Program.
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