Oxidant selection and evaluation for subsea power systems

The need to commercially, scientifically and militarily exploit the oceans has increased dramatically over the last 30 years. With this requirement has been generated the need for efficient underwater vessels capable of extended endurance, autonomy, high reliability and increased power density. In the past the majority of these vessels have been powered by secondary batteries, however, with the previous criteria in mind, batteries are in many instances no longer capable of meeting mission objectives. Advancements in air independent heat engines requires the use of stored chemical energy, normally in the form of hydrocarbon fuel and an oxidant. In the latter case, the oxidant volumetric and gravimetric storage densities can be changed by storing or deriving the oxygen from several different sources such as pure oxygen, oxygen rich compounds and oxygen extraction from seawater by electrolysis or membranes. Each oxygen source offers a different oxygen liberation capability, as well as dissimilar storage densities. Apart from the physical properties of the different oxidants, they each require a different type of containment and operating system. All of these factors will affect the total oxygen system weight and volume requirements. To understand the trade-offs involved in the oxidant system used for a particular vehicle and mission profile, this paper assesses the selection and evaluation of the possible oxygen sources required for hydrocarbon fuelled heat engines.