Energy generation from metal-water reaction for power systems, underwater and aerospace propulsion applications

The performance of a fuel, or propellant, depends critically on its combustion characteristics which have a direct impact on the system performance, reliability, long-term stability and environmental footprint. Also, cost, operability and material availability must be considered. Based on what has already been investigated in previous studies, metal fuels can be combusted with water or even with air as oxidizers to generate heat for many applications. Furthermore, when they are burned with air, low-net-carbon emissions can be achieved by capturing and recycling the combustion products. When metals react with water under specific conditions, it produces hydrogen on demand in exothermic reactions. Metals can be produced with clean primary energy through electrolysis, or other methods, and then store this energy as a chemical one in the metal fuel that can be released through oxidation by air, water, or even carbon dioxide, amongst other oxidants. Metals represent a promising solution for the future of propulsion and energy-conversion applications due to their reactivity with water, high energy densities and wide availability. However, as it is demonstrated in other studies, there are key limitations about the waste of the thermal energy in the case of low-temperature reactions and the waste of the chemical energy contained within the generated hydrogen as a reaction product in the case of high-temperature propulsion applications. Also, this concept when applied for onboard vehicles presents a number of difficulties related to storage systems and reaction rate kinetics. The objective of this work is to explore and investigate relevant, recent alternatives for developing clean energy with high performances based on hydrogen generation from metal-water reactions, focusing basically on rocket propulsion. The main characteristics of energy from metal fuels are numerically investigated and compared to the ones of the conventional, existing fuels. The techniques that are to be possibly used for exploiting the energetic potential of metal-water reactions are as follows: low-temperature metal-water reactors for fuel cells or other power systems, and high energy densities metals and water mixtures as propellants for underwater and aerospace propulsion. Thus, the exhausted hydrogen as a reaction product can act as a secondary fuel, enhance the combustion performance and produce thrust.