N112-155 TITLE: Bladder Fuel/Oxidizer Delivery System for Underwater Vehicles (UUVs) and Weapon Applications

TECHNOLOGY AREAS: Ground/Sea Vehicles, Weapons

OBJECTIVE: Develop and demonstrate a bladder storage and delivery system to supply reactants used in air independent propulsion systems. Current R&D propulsion related efforts for both Unmanned Undersea Vehicles (UUVs) and Torpedoes are investigating the use of liquid fuels and oxidizers. Due to the mass and volume constraints and air independent nature of the system, traditional tank designs relying on displacing the consumed reactant volume with gas and/or liquids are not suitable. Therefore the technology utilizing bladders to contain the reactants where by the displaced volume is either backfilled with reaction byproducts or external seawater is required. The bladder design should be adaptable to a variety of reactant types and provide a robust cost effective means for delivering the reactants. This type of system will also address corrosion issues and the high replacement/maintenance costs of fuel tanks in weapon applications. Additionally, the corrosion associated with utilizing seawater as a back fill medium has a significant total ownership cost burden.

Identification of novel bladder material properties to allow its elastic deformation (linear or non-linear) to be the driving force to expel the stored reactants and/or mitigate the pumping power to do so; this could eliminate/reduce delivery pump/motors allowing for higher system efficiency. The use of bladders as the storage/delivery system for UUVs will provide a path to address the demand of increased endurance missions from days to months. These bladders can provide the means to store/deliver fuel and oxidizer for UUVs, by providing multi-use opportunities and reduce the burden of limited weight/volume/buoyancy issues associated with UUVs.

A bladder system had been used in the past for undersea applications; however, this system was a one-time use and lasted for hours; the current topic is looking for a bladder system that will provide multi-use applications (fill/discharge/refill) for several weeks to months of operation.

DESCRIPTION: Several air-independent energy system efforts are currently being researched. These efforts include both electrochemical (i.e., solid oxide fuel cells, proton exchange membrane fuel cells, etc.) and thermal based (bipropellants, monopropellants, etc.) systems. Both fuel cell systems utilize liquid based reactants (i.e. borohydride, dodecane, hydrogen peroxide). Torpedo propellants in more recent times have focused on the use of Otto Fuel II. The bladders must meet the stringent compatibility requirements of the reactants (i.e., concentrated hydrogen peroxide, caustic solutions, acidic solutions, Otto Fuel II, HAN, etc). In order to maximize energy density, the bladders must be capable of being fully discharged with little remaining residual reactant. Additionally, to minimize total ownership cost, the bladder system should be capable of being drained and refueled via a simple through hull penetration which does not require the disassembly of the shell sections.

The current torpedo propellant Otto Fuel II has a density greater than water and is immiscible with water. This allows for the simple displacement using seawater during torpedo operation. Otto Fuel II is also immiscible with water, but forms a corrosive interface layer at the water propellant interface causing fuel tank corrosion. Post test operations require the separation of seawater from the propellant prior to reuse. Research is currently underway to develop an aqueous based propellant in order to replace the current Otto Fuel II system. Therefore the current seawater displacement technique will need to be replaced by a system such as a bladder.

Therefore, an innovative comprehensive bladder storage/delivery/refuelable system is sought to address the needs of several air-independent energy systems (i.e. fuel cell powered UUVs and torpedoes). To meet nominal undersea vehicle power requirements, fuel delivery rate requirements will range from much less than a gallon per minute to 10 gallons per minute with the storage volume ranging from less than 10 gallons up to 100 gallons.

The current topic is looking for a bladder delivery/storage system that will provide multi-use applications (fill/discharge/refill) and for several weeks to months of operation. In addition, identification of bladders with elastic deformation material properties to enable bladder designs capable of high fill/empty volume ratios for efficient storing & delivering of fluids. The elastic nature of these materials will enable expulsion of the fluids resulting from bladder contraction to minimum volumes as well as better accommodate/prevent rupture attributed to overfill. The internal environment in which the bladder will typically be located will require the bladder system to be resistant to abrasion, irregular surrounding geometries (i.e., rib stiffeners, communication tubes, etc.), high ambient pressure, and be resistant to wear associated with "pinch off". Bladder designs utilizing both hyper elastic and reinforced collapsible membranes are sought.

PHASE I: Demonstrate the use of a fuel bladder system to store and deliver liquid reactants such as Otto Fuel II, HAN, H2O2, NaBH4, seawater, etc with less than 1% residual fuel remaining upon discharge. The compatibility of the bladder material to 30 days of storage of the liquid reactants at temperatures ranging from -10 to 85oC at relative high humidity.

PHASE II: Construct and evaluate a comprehensive liquid reactant storage/delivery/refuelable bladder system. Test the system at full scale, to determine residuals, fill/refill procedures, etc. The system should be made available to the Navy for evaluation and testing within a vehicle to determine orientation effects during operation and refilling. Bladder systems must also demonstrate long term storage capability of liquids (up to 10 years).

PHASE III: Design and construct a fully integrated comprehensive bladder delivery system for a UUV Energy section.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: This bladder approach can also be used for the DOE�s fuel cell efforts for automobiles, NASA�s fuel cell approaches and other Navy fuel cell efforts (portable power, AUVs, USVs reactant storage applications).

REFERENCES:
(1) UUV Master Plan, www.navy.mil/navydata/technology/uuvmp.pdf

(2) Naval S&T Strategic Plan, https://www.onr.navy.mil/

KEYWORDS: Bladder, fuel cell, reactants, fuels, oxidizers,

** TOPIC AUTHOR (TPOC) **

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