Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item PRESSURE LOSSES IN A NOVEL, VISCOUS SPACECRAFT PROPELLANT AND IMPACTS ON COMPATIBILITY WITH TRADITIONAL MONOPROPELLANT ARCHITECTURES(2024) Walsh, Timothy; Cadou, Christopher; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydrazine offers a unique list of benefits as a spacecraft propellant that have made it the most selected fuel for chemical in-space propulsion, either in its pure form or as one of its derivatives. This is true for both monopropellant and bipropellant applications, as one of pure hydrazine’s many benefits is the ability to simultaneously operate in both modes. However, hydrazine is also very hazardous and requires significant logistics to work with on the ground. As a result, there has been an industry-wide search for high-performance replacements that mitigate the hazards and associated logistics. These have been collectively termed ‘green propellants’. Two of the most well-known green propellants, ASCENT and LMP-103S, are ionic liquids that propose to completely replace hydrazine. The focus of this thesis is a third green propellant known as Green Hydrazine Propellant Blend (GHPB). GHPB retains hydrazine as a base constituent, but as a hybrid between the conventional and ionic classes of propellants, it is considered less hazardous. Unlike the previous green propellants, GHPB is designed to be used as a ‘drop-in’ replacement with existing hydrazine architectures. However, it is much more viscous than hydrazine leading to uncertainties about pressure losses and cavitation. The objective of this thesis is to relieve some of this uncertainty by measuring pressure loss and flow rate in four common propulsion system components (a latch valve, a filter, and two venturis) over a range of flow rates that are representative of those encountered in an operational spacecraft. The data are used to infer the minor loss coefficient (for non-cavitating flows) and the discharge coefficient (for cavitating flows) as functions of flow rate for each component. Knowing the values of these coefficients is crucial for predicting thruster injection pressures and hence for designing a propellant delivery system. The values of these coefficients as well as the true pressure losses are plotted as functions of flow rate. Pressure losses are found to be approximately 5 times higher than those associated with hydrazine for a given flow rate. These results are put into context by using them to calculate the pressure distribution in the propulsion system of the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) spacecraft if hydrazine were replaced with GHPB. The results show that total pressure losses would be 3-14 times greater with GHPB than with hydrazine over the course of the PACE mission. However, GHPB’s higher viscosity also reduces the amplitude of pressure transients associated with startup by about a factor of 3. This means that the venturis needed to protect valves from startup transients in hydrazine-based systems are not needed with GHPB. Eliminating the venturis reduces the total pressure losses associated with GHPB to 1.7 – 8.5 times those associated with hydrazine.Item Advancing Nitrous Oxide As A Monopropellant Using Inductively Heated Heat-Exchangers: Theory and Experiment(2019) Saripalli, Pratik Sharma; Sedwick, Raymond J; Yu, Kenneth; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Most monopropellant thrusters used for attitude control and station keeping employ hydrazine as their propellant. In recent years, significant effort has been focused on finding an alternative due to its high toxicity. This work focuses on advancing nitrous oxide, a green monopropellant with a strong performance capability, as a replacement for current monopropellant thrusters. A large emphasis is placed on trying to address catalyst degradation experienced in most thrusters due to the high temperatures from decomposition. The approach described here eliminates the dependence for a high catalytic surface area, typically decreased from degradation, and catalysts altogether by using high temperature porous heat exchangers. A 1-D numerical compressible fluid model was created to model a typical decomposition chamber and simulate self-sustained decomposition of nitrous oxide. It implements a preheated, thermally-conductive, metal foam as the heat exchanger. An extensive parameter study was conducted to help understand thermal and fluid effects on steady-state decompositions. Using a copper metal foam, steady-state solutions simulated successful nitrous oxide decomposition, with an exit gas temperature around 1345 K. Simulations were extended to other high temperature metal foams with different thermal conductivities and melting points. Modeling flow rate conditions more representative of current monopropellant thrusters required scaling of the decomposition chamber in order to be self-sustaining. Experiments were conducted using results from the numerical simulations as guidelines. Three different heat exchangers (copper metal foam, copper discs, and stainless-steel discs), all of which have significantly less effective surface area than nominal catalysts used in thrusters, were tested for nitrous oxide decomposition. These heat exchangers were preheated to thermal decomposition temperatures using an inductive heating system and placed in a vacuum bell jar to mitigate heat loss to the environment. Testing with copper metal foam resulted in complete degradation of the heat exchanger due to oxidation from nitrous oxide decomposition. A set of copper discs, uniquely designed to maximize tortuosity of the flow, was implemented in an attempt to address the oxidation issues. While the preliminary test did confirm steady-state decomposition of nitrous oxide within the heat exchanger, further tests resulted in temperatures exceeding the melting point of copper within the discs. The last heat exchanger was a set of stainless-steel discs of the same design. Repeated tests all successfully achieved steady-state decomposition of nitrous oxide within a two-minute interval.