Powder Fuel System Development for Hybrid Propulsion and Power

The proposed development effort will build upon our team's FY18 work to develop a modeling and simulation capability to estimate the performance of powder-fed hybrid engines. The FY19 effort will focus on developing and characterizing instrumented powder fuel system hardware that will demonstrate proof-of-concept operation, as well as proposing modifications necessary to create lighter-weight hardware suitable for flight test. Our team has worked with John Foote of MSFC to deliver an existing, benchtop positive-displacement fluidized bed (PDFB) to LaRC to characterize its performance in terms of fuel-to-carrier gas mass ratio and fuel mass flow rate as a function of carrier and driving gas pressure. The proposed work will progress by testing new PDFB hardware architectures and designs to improve the same mass delivery metrics using rigorous, statistical engineering methodologies. Design changes will also be implemented to improve the mass ratio between the system hardware and the powder media, as well as volume of the hardware relative to the powder media. \n\n The proposed effort will benefit missions requiring novel propulsion and power systems that can operate using ambient resources. During the FY18 effort, our team has undertaken ongoing trade studies to assess accessing various latitudes on Mars while delivering 20 metric ton payloads from orbit using lifting bodies and atmosphere-breathing hybrid engines. Due to the technology's flexibility, further systems analysis efforts could evaluate hybrid systems burning alternative mixtures, such as aluminum and water, for mission destinations assuming at least the latter would be locally present.\n\nTechnology development will yield other benefits to NASA, including:\n\xb7 Development of powder-fuel injection hardware emphasizing metrics of interest for flight testing, including system packaging and mass flow rate of delivered fuel. The powder-fuel injection system would use universal connections to allow it to interface to various downstream technologies and be used in a variety of mission architectures. This would allow, to a degree, the fueling system to be developed in parallel with, or independent of, technologies requiring its use. Furthermore, the types of fuels would not be limited to pure metal powders - it is anticipated there would be flexibility to other powdered fuels of interest to the hybrid propulsion community both for Earth and space missions. \n\xb7 Workforce development and training in propulsion systems design and analysis, as the proposed development effort would make use of early career (PI and team members) and student (NIFS) researchers.\n\nWhile the technical feasibility of fluidized beds using powdered media has been established in previous studies, technical risks remain in the development of the proposed technology.\n\xb7 The safety of the fueling system needs to be proactively treated due to the requirements of using a high-pressure systemwith a combustible powder. Near term steps will be to use a magnesium surrogate in the form of SiO2,which is inert and within 10% of the density of magnesium, as well as oven-dryable from test-to-test as needed. Other requirements such as filtering will be considered in the plenum into which the surrogate will be injected. The team is currently taking steps to prioritize safety into all initial designs in consultation with AESB personnel.\n\xb7 The fueling system may not be performant, or there may be conditions where fuel system becomes clogged. To mitigate this, statistical engineering approaches will parameterize the design and boundary conditions of the system to model its performance and identify optimum design settings. The ability to test different methods of gas injection to the PDFB will be designed into the experiment with inserts that can swapped. Furthermore, statistical modeling techniques will be used to identify the probability of system success given inputs of system parameters (e.g., fuel particle size, supplied pressure, etc.)\n\nThe proposed one-year effort (TRL 3-4, TRL 4 targeted) will advance the state-of-the-art of powder fueling toward being able to conduct flight tests of hybrid propulsion systems leveraging the technology. Primary objectives are to characterize baseline system performance and produce designs improving on fuel-to-carrier-gas mass ratio, fuel mass flow rate, and packaging. Secondary objectives include systems analysis for mission context and design requirements. Deliverables of the funded effort will be fueling system design, hardware, and computer models to provide predictions of systems behavior. Preliminary combustor design and flight test recommendations for follow-up work will also be delivered.

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