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High-pressure pumps with minimal mechanical interfaces for low lubricity fuels

Description:

OBJECTIVE: Design, develop, and demonstrate innovative methods of pressurizing low-viscosity and low-lubricity fuels for delivery to high-pressure fuel injection systems that avoid or reduce sliding mechanical interfaces vulnerable to inadequate lubrication. DESCRIPTION: High pressure common rail (HPCR) injection systems are used in internal combustion (IC) engines for several Army aviation and ground engines to deliver necessary propulsion power under harsh operating conditions. The HPCR IC engines and their components are designed for diesel fuels, however, they are typically operated with F-24 jet fuel by the US Army and other DoD branches. The properties of F-24 that are important to HPCR IC engine operation vary widely, such that some fuels that meet F-24/JP-8 specifications[1,2] may cause premature failure of HPCR fuel delivery components. Further, tactical independence of US Army units requires ability to operate outside of the established supply chains that provide fuel within established specifications. The broadening of the allowable fuel-property envelope will increase the ability of fast-moving, forward operating units to use the fuel resources that are immediately available in their environment. HPCR fuel pumps are sensitive to the lubricity of the fuels that they are pumping and are liable to fail prematurely when fuel lubricity falls below those of diesel and additivized jet fuel.[3,4] Fuel lubricity is based on chemical and rheological properties (viscosity) and can vary widely between diesel, jet fuel, synthetics, ethanol, and gasoline. Current high-pressure fuel pumps typically use cylinder-piston and cam designs that undergo sliding, reciprocating, and/or intermittent contact motions with significant loads at the points where various components come into physical contact. The vulnerabilities of these pumps is largely due to inadequate lubrication at those sliding and impacting mechanical interfaces combined with the tight tolerances that are needed to reach the desired fuel pressures. Innovative concepts and methods are sought to reliably pressurize low-lubricity fuels to high pressures of at least 2,500 bar while providing adequate flow. The resulting pump design is expected to increase robustness and reduce vulnerability to varying fuel properties by avoiding materials failures from inadequate lubrication of sliding and impacting mechanical interfaces by the working fluid. The target for the pump design are HPCR IC engines from commercial engine manufacturers used in class III unmanned aviation systems (UAS) and small-to-medium manned and unmanned ground systems (20 to 350 horsepower) for operation on standard military fuels (F-24, JP-8) and lower lubricity fuels (synthetic, ethanol blend, etc.). PHASE I: Formulate details of proposed pumping method that eliminates vulnerability to low lubricity fuels through novel designs, materials, and operational concepts that eliminate sliding and impacting interfaces, or reduce their severity (sliding speed and distance, contact pressure, etc.) and number significantly. Proposed methods to produce the required pressure and fluid flow rate may use a single stage or multiple stages, however, any method and surrounding design must significantly reduce the number and harshness of mechanical interfaces from current HPCR pump designs. Possible methods of producing pressurization and flow are centrifugal motion, magnetic fields, solid-state compression, and microfluidics, but solutions are not limited to these methods. Develop design of major pump components and concept of how they work together to achieve compression and flow while minimizing sliding mechanical interfaces. Demonstrate feasibility of pumping method(s) to meet the required pressure and flow metrics in Phase II in a conceptual pump design through a comparison of instrumented benchtop experiments and analytical and/or numerical modeling/simulation. Determine estimated power requirements of design. Analytically/numerically determine contact pressures, stresses, and sliding speeds of any sliding or impacting mechanical interfaces and provide an assessment of damage vulnerability to lubrication with low-viscosity fuels. Deliverables are the conceptual pump design, quantitative feasibility results, power requirements, and vulnerability assessment. PHASE II: Finalize component and pump designs from Phase I. Fabricate components and ensure expected operation through testing and comparison to feasibility model from Phase I. Integrate components together into working prototype. Demonstrate reliable operation of prototype using conditions for the North Atlantic Treaty Organization Allied Engineering Publication 5 (NATO AEP-5) standard (400 hours endurance plus before and after performance runs) on two fuels provided by the Army, F-24 jet fuel and one hydrocarbon fuel with no lubricity additives of 1 centiStoke viscosity at 40 °C, with the following requirements: simultaneously achieve at least a pressure of 2,500 bar (36,260 psi) at a flow rate exceeding 1.3 liters/minute; digital control of pump pressure and flow; use a readily-available vehicle power source (12- to 28-V electrical power, mechanical power on shaft); dry weight of less than 15 lbs.; combined length, width, and height of less than 40 inches. Provide evidence that pump could achieve operation for 3000 hours with no maintenance to meet typical IC engine overhaul intervals through accelerated endurance testing with start/stop cycles and flow rate variations. Deliver a working prototype to CCDC Army Research Laboratory for evaluation. PHASE III DUAL USE APPLICATIONS: Integrate prototype fuel pump into a HPCR IC engine from a commercial engine manufacturer in the 20 to 350 horsepower range and conduct engine tests of prototype with both a standard military fuel and a low-lubricity fuel. Such engines are also relevant to the multi-billion-dollar markets for lightand medium-duty commercial transport vehicles, farm equipment, and construction/warehouse equipment (cranes, loaders, etc.), as well as power generators in remote locations. A successful demonstration of a high-pressure pump tolerant to widely-varying fuel properties would enable flexible fuel standards and open up the widespread use of synthetic and alcohol fuel blends to meet increasingly stringent US and international fuel use standards. REFERENCES: 1. [1] Department of Defense Standard Practice Quality Assurance/Surveillance for Fuels, Lubricants and Related Products, MIL-STD-3004-1; NATO Standard AFLP–3747, “Guide Specifications (Minimum Quality Standards) for Aviation Turbine Fuels (F-24, F-27, F-34, F-35, F-37, F-40, and F-44),” Edition A, Version 1.; 2. [2] Detail Specification: Turbine Fuel, Aviation, Kerosene Type, JP-8 (NATO F-34), NATO F-35, and JP-8+100 (NATO F-37), MIL-DTL-83133J, 16 December 2015.; 3. [3] J.K. Klein, “PROPULSION AND POWER RAPID RESPONSE RESEARCH AND DEVELOPMENT (R&D) SUPPORT Delivery Order 0011: Production; 4. [4] G.R. Bessee, S.A. Hutzler, E. Frame, D.M. Yost, G.R. Wilson, N. Jeyashekar, and A.C. Brandt, “PROPULSION AND POWER RAPID RESPONSE RESEARCH; 5. [5] D.M. Yost, A.C. Brandt, and G.T. Hansen, “RAPID RESPONSE RESEARCH AND DEVELOPMENT (R&D) FOR THE AEROSPACE SYSTEMS DIRECTORATE,; 6. [6] D.M. Yost and E. Frame, “Rotary Fuel Injection Pump Wear Testing Using a 30%/70% ATJ/F-24 Fuel Blend,” U.S. Army TARDEC Fuels and Lubricants Research KEYWORDS: Fluidics, Lubricants and Hydraulic Fluids, Fuels, Reciprocating and Rotating Engines, Fluid Mechanics, Mechanics, Thermodynamics
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