THE PENNSYLVANIA STATE UNIVERSITY SCHREYER HONORS COLLEGE
DEPARTMENT OF AEROSPACE ENGINEERING
INJECTOR REDESIGN FOR A HYDROGEN PEROXIDE MONOPROPELLANT THRUSTER
MATTHEW D. WEHNER SPRING 2018
A thesis submitted in partial fulfillment of the requirements for a baccalaureate degree in Aerospace Engineering with honors in Aerospace Engineering
Reviewed and approved* by the following:
Rui Ni Assistant Professor of Mechanical and Nuclear Engineering Thesis Supervisor
Robert Melton Professor of Aerospace Engineering Honors Adviser
Amy Pritchett Aerospace Engineering Department Head Faculty Reader
* Signatures are on file in the Schreyer Honors College. i
ABSTRACT
The work performed in this thesis focuses on redesigning the injector in a hydrogen peroxide monopropellant thruster used for a prototype terrestrial flight vehicle. Preliminary injector concepts were drafted using computer-aided design, and basic simulation was performed to visualize possible flow scenarios. Injector designs were manufactured using 3D printing and were mounted on a 3D printed test rig that simulates the flow path upstream of the catalyst bed in the thruster. Water was flowed through injector designs to characterize their performance in terms of total flow rate and flow uniformity. Total weight flow was evaluated by collecting water flow over a period of 3 seconds. Flow uniformity was estimated by finding weight flow through certain portions of the injector, converting to velocity, and then finding an area-weighted flow uniformity index. A model closely resembling the original injector design and one new design were tested.
The redesigned injector yielded 6% higher total weight flow but had a 32% lower flow uniformity index, so further work is required to arrive at a final design. To fully integrate the new design with the flight vehicle, qualification testing with the new injector in the peroxide thruster must be performed.
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TABLE OF CONTENTS
LIST OF FIGURES ...... iii
LIST OF TABLES ...... iv
ACKNOWLEDGEMENTS ...... v
Chapter 1 INTRODUCTION ...... 1
Background ...... 1 Scope ...... 3
Chapter 2 INJECTOR DESIGN CONSIDERATIONS ...... 4
Original Injector Design Overview ...... 4 Goals of New Injector Design ...... 8 Redesign Process ...... 11
Chapter 3 PRELIMINARY INJECTOR REDESIGN AND FLOW ANALYSIS ...... 13
Overview of SolidWorks Flow Simulation ...... 13 Injector Design 0 ...... 14 Injector Design 1 ...... 16 Injector Design 2 ...... 17
Chapter 4 FLOW TEST OVERVIEW ...... 19
Experimental Method ...... 19 Flow Test Equipment ...... 21
Chapter 5 DATA ANALYSIS AND RESULTS ...... 25
Data Analysis ...... 25 Flow Test Results ...... 25
Chapter 6 CONCLUSION ...... 29
Appendix A TEST STAND P&ID ...... 31
BIBLIOGRAPHY ...... 32
iii
LIST OF FIGURES
Figure 1: Puma Vertical Flight Test ...... 2
Figure 2: Original Injector ...... 4
Figure 3: View of catalyst bed from PE01 ...... 6
Figure 4: View of injector down engine chamber ...... 7
Figure 5: View of retaining ring on injector ...... 7
Figure 6: Cutaway of engine showing the injector in blue and the catalyst bed in red ...... 8
Figure 7: Assembly used for SolidWorks Flow Simulation ...... 14
Figure 8: Top-down view of Injector Design 0 ...... 15
Figure 9: Injector Design 0 flow simulation results ...... 15
Figure 10: Isometric view of Injector Design 1 ...... 16
Figure 11: Injector Design 1 flow simulation results ...... 17
Figure 12: Isometric view of Injector Design 2 ...... 18
Figure 13: Injector Design 2 flow simulation results ...... 18
Figure 14: Diagram of injector flow regions ...... 20
Figure 15: PETS-II ...... 22
Figures 16a-c: Flow diverters for flow bounded by the outer limits of regions 1, 2, and 3 ..... 23
Figure 17: Flow diverter setup ...... 24
Figure 18: Data analysis spreadsheet example ...... 25
Figure 19: Injector Design 0 flow velocity profile...... 26
Figure 20: Injector Design 2 flow velocity profile...... 27
iv
LIST OF TABLES
Table 1: Flow test data ...... 27
v
ACKNOWLEDGEMENTS
The work done for this thesis would not have been possible without the help of Lunar Lion propulsion lead Max Winn who led the effort to build the engine test stand that was a crucial component of the water flow testing done to quantify injector performance. I would also like to thank the previous Lunar Lion propulsion leads for their contributions to the program.
Additionally, I express my gratitude for former Lunar Lion Mission Director Michael Paul and current Lunar Lion Faculty Advisor Dr. Alex Rattner for the creation and continued support of a program that has given dozens of Penn State students the opportunity to get hands-on experience with prototype spacecraft. Furthermore, I want to give thanks to the members of the Lunar Lion propulsion team during the Spring 2018 semester, particularly Mike Harshell and Ravi Patel who assisted with the water flow experiment. I want to thank Dr. Rui Ni for his insightful guidance through the development of my project. Finally, I want to express my gratitude to my honors adviser Dr. Robert Melton giving academic and professional advice during my time at Penn State.
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Chapter 1
INTRODUCTION
Background
The Penn State Lunar Lion Team is a team of primarily undergraduate students that has been working toward developing a prototype lunar lander since its inception in 2012. After originally focusing on using a bipropellant combination of liquid oxygen and ethanol, the team chose to switch to hydrogen peroxide monopropellant thrusters in 2015. The thrusters were purchased from Tecnologia Aeroespacial Mexicana, a commercial manufacturer of liquid rocket engines. Starting the summer of that year, significant qualification and acceptance testing was performed on four out of the five thrusters the team had purchased. From testing, it was determined that the hydrogen peroxide monopropellant thrusters were a suitable candidate for integration with a flight vehicle. In the summer of 2016, the engines were integrated onto the Lunar Lion Team’s first flight vehicle, Puma, and the craft underwent successful static tests. In the fall of 2016, Puma completed its first vertical flight test, which is shown in Figure 1. 2
Figure 1: Puma Vertical Flight Test After Puma was retired, the team began work on a newer, more powerful flight vehicle called Lynx, which is still under development as of spring 2018. Since the days of the first engine tests, members of the Lunar Lion Team discovered that the engines in their original configuration left much to be desired in terms of performance. When moving the engines from Puma to Lynx, it was decided that more qualification and acceptance testing would be needed since one engine has never been fired. This presented an opportunity to make some improvements to the engines before integration on the new vehicle. In her thesis titled “The Qualification and Acceptance Testing of
Hydrogen Peroxide Monopropellant Thrusters”, former Lunar Lion propulsion subsystem lead
Kara Morgan recommended redesigning the injectors in the hydrogen peroxide engines to improve performance [1]. This thesis outlines efforts made to do so. 3 Scope
This thesis outlines the efforts taken to redesign the injection system used in the hydrogen peroxide thrusters currently used by the Penn State Lunar Lion Team. Only showerhead-style injection systems were considered.
Preliminary injector replacements were designed and modeled in SolidWorks. To visualize the flow behavior through the injector designs, a model of the chamber upstream from the injector was created, and SolidWorks Flow Simulation was used to generate flow trajectories.
Experimental validation of injector redesign was performed by flowing water through three injector designs. Although the 90% hydrogen peroxide mixture used for the rocket propellant has a higher density to water (1.39 vs 1 g/cm3), it was assumed that water would yield similar flow characteristics [2]. To simulate the whole injection system, a 3D-printed model of the top portion of the engine was mounted on a test stand built to test the engines. Nitrogen was used as the source of pressure for the flow.
A comparison of injector performance was achieved by measuring total weight flow through each injector design and evaluating the uniformity of the flow field exiting the injector by measuring weight flow through certain portions of the injectors to calculate an area-weighted uniformity index. 4
Chapter 2
INJECTOR DESIGN CONSIDERATIONS
Original Injector Design Overview
When originally delivered to the Lunar Lion Team, the hydrogen peroxide monopropellant thrusters in question had a simple showerhead injection system. Each engine has a 1/4-inch NPT fitting at the top to accommodate the incoming flow, which enters a small chamber ahead of a 1/4- inch flat plate with several holes drilled through it. The stream hits a flat portion of the plate, spreads itself by deflection, and exits through the holes into a chamber of transition metals that decompose the hydrogen peroxide into water vapor and oxygen gas. The holes in the injector are arranged in four concentric rings. Figure 2 shows an image of the injector when removed from engine PE01, the test article that endured the most hot-fire tests during initial qualification and acceptance testing.
Figure 2: Original Injector 5 It is important to note that the hole size and pattern is irregular due to the injectors being manufactured by hand without the aid of a computer-controlled machine. This means that injection is not be consistent across all engines.
Another issue with the injector design that was uncovered during qualification and acceptance testing was the lack of adequate pressure drop across the injectors. During testing, pressure oscillations from decomposition in the catalyst bed were measured upstream of the engine, and the test stand experienced violent shaking. To protect the sensitive hardware on the test stand and later test vehicles, 1/8-inch orifices were installed upstream of the engines, which led to an 11% pressure drop. System pressure was increased from 500 to 800 psi to accommodate this change [1].
The main indication that the current injector design has not been performing well is that the catalyst bed on PE01 shows uneven wear from 80 hot-fire tests during qualification and acceptance testing and another 23 during Puma static and vertical flight testing. Upon inspection of the top of the catalyst bed, there was uneven discoloration on the side that rests against the injector plate. A dark ring on the top of the catalyst bed is visible with a lighter region in the center, which is directly under the portion of the injector plate with no holes. This could indicate that the propellant is flowing faster out of the inner holes and putting more wear on that part of the catalyst bed. Figure 3 shows the catalyst bed stack when removed from PE01. 6
Figure 3: View of catalyst bed from PE01 Another observation made on the current injector design when disassembling the thruster was that the outermost holes on the injector are partially obscured by a retaining ring that helps hold the injector inside of the engine and a screen up against the injector. This ring could prevent propellant from flowing through the outermost holes. Figure 4 shows the retaining ring in place when the injector is installed on the engine, and Figure 5 shows a detailed view of the retaining ring blocking holes in the injector.
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Figure 4: View of injector down engine chamber
Figure 5: View of retaining ring on injector A major constraint on the design of the injector is the small amount of space between the peroxide stream entering the engine and the catalyst bed. This designer of the engines likely made this choice to maximize the amount of catalyst bed in the engine. However, it leaves little space to expand the incoming stream to the whole diameter of the chamber. To demonstrate the short distance over which the flow must be expanded, Figure 6 shows a cutaway view of a CAD model 8 of the engine. To comply with International Trade and Arms Regularions (ITAR) export controls, all dimensions are absent from the diagram.
Figure 6: Cutaway of engine showing the injector in blue and the catalyst bed in red
Goals of New Injector Design
The new injection system should achieve three main goals: it should provide an adequate pressure drop between the incoming stream and the engine’s chamber, it should distribute the flow as evenly as possible, and still maintain a high flow rate.
The addition of the 1/8-inch orifice has helped achieve a pressure drop high enough to effectively render the pressure measured upstream of the injector independent of the chamber pressure. A similar gradient may be achieved by using an injector plate with an adequate pressure 9 drop, which would eliminate the need for the 1/8-inch orifice. Using the Darcy-Weisbach equation, pressure drop over the restricting orifice is
퐿 휌푢2 ∆푝 = 푓 (1) 퐷 퐷 2 where ∆p is pressure drop, fD is the experimentally-determined Darcy friction factor, L is the length of the pipe element, D is the diameter of the pipe element, ρ is the density of the fluid, and u is the fluid velocity. Using an equation from Handbook of Hydraulic Resistance, pressure drop over the injector plate is [3]
휌푢2 ∆푝 = 푘 ( ) (2) 2 where
0.75 1.375 2 푙 1 푘 = [0.5(1 − 푓) + 휏(1 − 푓) + (1 − 푓) + 0.02 ] 2, (3) 푑ℎ 푓
푓푙표푤 푎푟푒푎 푓 = , (4) 푎푟푒푎 표푓 푝푖푝푒
휏 = (2.4 − 푙)̅ 휑(푙̅), (5)
0.535푙8̅ 휑(푙̅) = 0.25 + , (6) 0.05+푙7̅ and
푙 푙̅ = . (7) 푑ℎ
Here, l is the thickness of the injector plate, and dh is the diameter of the holes in the plate.
The current injection system uses the sum of both pressure drops to achieve the required total pressure drop to render the chamber pressure independent of the pressure ahead of the injector
(typically ~30%). To achieve the required pressure drop with only the injector plate, the value of f decreases by reducing the number of holes and/or area of its holes. Solving for the pressure drops will not be possible until experiments measure flow rate, so this thesis will seek to develop new 10 injector solutions using the 1/8-inch orifice before trying to develop solutions that do not require the orifice.
The evenness of the flow coming out of the injector plate and into the catalyst bed will affect the rate at which liquid peroxide changes into gas that provides thrust when expanded through a nozzle. Simply put, the more evenly flow spreads over the catalyst bed, the more thrust will be generated by the engine. A uniform flow will also help increase the life of the catalyst bed by preventing certain portions of the flow from wearing more quickly than others do. Some rocket engine injectors use impinging jets instead of a simple showerhead injector to help atomize the flow for improved decomposition. For this thesis, impinging jet injectors are not considered because they have a longer response time (the time required for the chamber pressure to rise to
90% of the steady-state chamber pressure) than simple showerhead injectors do [4]. This attribute is unfavorable for small-scale peroxide thrusters since having a shorter response time allows for quicker “burp sequences”, which are short burns used to warm up the engines before firing them.
Longer burns would waste more propellant, so therefore this redesign project will not consider impinging jet injectors.
For showerhead injectors, the geometry of the hole pattern on the injector plate along with the shape of the center section of the plate determines the distribution of the flow over the catalyst bed. For the scope of this thesis, the current scheme of four concentric rings of holes will remain.
Only the size and number of holes in each ring will change. The location of the rings will change from the current design but will not vary between subsequent designs. This thesis also explores the use of a conical diverter in the center section of the injector plate to help spread the flow.
Finally, the injector design should maintain a high overall flow rate into the catalyst bed.
As given by the thrust equation 11
푊̇ 휏 = 푢 , (4) 푔 푒푞 where τ is thrust, 푊̇ is weight flow rate, g is standard gravity on Earth, and ueq is the equivalent exhaust velocity of the engine, thrust is directly proportional to the weight of propellant that can be flowed through the engine per unit time. Certain designs that facilitate an even flow and adequate pressure drop may negatively affect the flow rate, negating performance increases. New injector designs should at least maintain the flow rate achieved by the current setup.
Redesign Process
To facilitate the development of a new injector solution, this thesis implements an iterative process used to design, manufacture, and test new injector plates. First, SolidWorks CAD is used to generate a 3D model of a potential injector design. Next, injector designs are brought into a
SolidWorks assembly containing a model of the portion of the engine upstream of the injector, and flow simulation is used to simulate the peroxide flow entering the engine. The results of the fluid simulation are evaluated for flow uniformity, and adjustments are made until desired flow characteristics are achieved in simulation. Once a design iteration is deemed significant enough to warrant experimental testing, it is manufactured using 3D printing with nylon. The manufactured sample is attached to a 3D-printed model of the portion of the engine upstream of the injector, which is mounted to an engine test stand. Water is then flowed through the injector with nitrogen as the pressure source, and time-averaged weight flow rate is calculated. Flow uniformity is evaluated by measuring the flow velocity profile through the four concentric regions of the injector. This is accomplished by diverting the using with 3D-printed components and measuring 12 the weight flow through each region. All fluid flow testing is performed at a pressure far less than the normal operating pressure of the engines since the nylon material used is far weaker than the stainless steel used to manufacture the engines. After testing, injector designs may modified in
SolidWorks and 3D printed again. By using rapid manufacturing techniques, this entire process can be repeated quickly at a low cost.
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Chapter 3
PRELIMINARY INJECTOR REDESIGN AND FLOW ANALYSIS
Overview of SolidWorks Flow Simulation
For this thesis, SolidWorks Flow Simulation provides a simple visualization of flow paths through injector designs. The flow simulation package provides a high level of functionality for its ease of use, but it does not yield results that are as accurate as more advance simulation packages such as ANSYS. Since the flow out of the orifice and onto the injector plate features complex interactions between streams, its results provide qualitative overviews of flow uniformity rather than provide any useful numerical data.
For flow simulation, a SolidWorks model of the portion of the engine upstream of the injectors was created. The model is of the same piece that will be 3D-printed for use in water-flow testing. To be secured on this component, the injector designs feature extra material around the central perforated region to allow the pieces to be bolted onto the test rig. Additionally, a 3D model of the 1/8-inch orifice sits in the upstream portion for reference when establishing the boundary condition of the incoming flow. Figure 7 shows a cutaway side view of the assembly used for flow simulation. 14
Figure 7: Assembly used for SolidWorks Flow Simulation For all SolidWorks Flow Simulation analysis, a boundary condition of weight flow from earlier estimates was applied to the 1/8-inch hole in the orifice as a fully developed inlet flow.
Velocity contours are used for results.
Injector Design 0
Injector Design 0 maintains almost all aspects of the original injector design and features four concentric rings of holes. The most notable changes from the original design are that the hole spacing and hole diameters are standardized. Additionally, the outermost ring of holes were moved closer to the center of the injector to eliminate potential impingement with the retaining ring used to hold the injector in place. This may also help reduce channeling, a problem where some propellant goes around the catalyst bed in the chamber and does not decompose. This injector design will serve as a basis of comparison for other injector designs since it is largely unchanged from the original injector. These changes only serve to accommodate the flow diverters used for flow profile measurements as they are not adjustable and require a certain hole spacing. Figure 8 shows a top-down view of Injector Design 0. 15
Figure 8: Top-down view of Injector Design 0
For Injector Design 0, SolidWorks Flow Simulation showed a flow biased toward the outer regions of the injector, and Figure 9 shows this result.
Figure 9: Injector Design 0 flow simulation results This result is not the same as the guess made from inspecting the wear at the top of the catalyst bed. Experimental analysis will further explore this discrepancy.
16 Injector Design 1
Injector Design 1 takes the same hole pattern from Injector Design 0 and adds a conical flow diverter. The addition of the diverter aims to reduce the resistance from the flat section in the center of the injector by providing a smoother transition, and Figure 10 shows a model of the design with the new flow diverter highlighted.
Figure 10: Isometric view of Injector Design 1 SolidWorks Flow Simulation results show a flow that is heavily biased toward the center, which is shown in Figure 11. 17
Figure 11: Injector Design 1 flow simulation results Although this result is not desirable, Injector Design 1 serves as useful step in the design process since it suggests that the conical diverter will yield center-biased flow. With this design expecting to favor central flow and the original injector design expecting to favor flow toward the outside, experimental test data will show how well simulation predicted actual results.
Injector Design 2
Injector Design 2 aims to find a balance between the outwardly biased flow from Injector
Design 0 and the centrally biased flow from Injector Design 1. To accomplish this balance, the most central hole size was reduced, and the number of holes in that layer were also reduced. Figure
12 shows an isometric view of the injector design with the changes from the previous design highlighted. 18
Figure 12: Isometric view of Injector Design 2 After experimenting with different hole diameters and dimensions for the central cone, flow simulation results still showed flow paths that favored the outer or inner portion of the injector and were not evenly distributed over the full injector. A balance was eventually found when flow results showed most flow split between the innermost and outermost rings of holes. Still, the accuracy of this particular flow simulation will not be known until experiments are done. Figure
13 shows the results of flow simulation for Injector Design 2.
Figure 13: Injector Design 2 flow simulation results 19
Chapter 4
FLOW TEST OVERVIEW
Experimental Method
Flow testing aims to gather data for the total weight flow through injector designs and generate flow profiles through the four radial regions of the injectors. Water replaces the 90% hydrogen peroxide propellant as the working fluid to avoid the dangers of potential decomposition.
The Peroxide Engine Test Stand II (PETS-II), a test stand developed by the Lunar Lion Team to characterize engine performance, will flow water through 3D-printed injector designs. 3D printing allows for quick manufacturing of test specimens to enable an iterative rapid prototyping process.
To protect the samples from damage, the test stand will run at a lower pressure than it would for actual engine tests. For injector flow testing, the test stand will run at a pressure of approximately
95 psi ahead of the injector to stay within the range of safety but still allow for a well-developed flow.
Total weight flow data is gathered by simply collecting the water flowed through the injector over a certain period. Tests for weight flow are run for 3 seconds, which is long enough to minimize the effects of startup transients but short enough to minimize the effect of pressure depletion in the test stand. The exact time between activating and deactivating the solenoid that controls the valve that starts and stops flow through the injector is measured with a stopwatch to 20 ensure accuracy. Flow tests are run three times each and the average values are used for further calculation. Time-average weight flow is given by
푊 푊̇ = 푇 (5) 푇 푡 where WT is the total weight of water collected under the injector and t is the flow time measured by the stopwatch.
This experiment measures the flow profiles through a similar process, but uses 3D-printed flow diverters to measure weight flows through specific regions of the injector designs. Like the total weight flow rate tests, flow profile tests run for 3 seconds. For reference, the flow is divided into the four regions shown in Fig. 14.
1 2 3 4
Figure 14: Diagram of injector flow regions
The weight flows through regions 1-4 are
푊 푊̇ = 1 (6a) 1 푡
푊 푊̇ = 2 − 푊̇ (6b) 2 푡 1 21 푊 푊̇ = 3 − 푊̇ − 푊̇ (6c) 3 푡 2 1
푊̇ 4 = 푊̇ 푇 − 푊̇ 3 − 푊̇ 2 − 푊̇ 1 (6d) where W1-4 are the total weights of the water collected inside of the outer limits of regions 1-4. The subtraction in equations 6a-d result in 푊̇ 1−4 being the weight flows only through those regions.
Neglecting the effects of friction, effective flow velocity through each region is
푊̇ 1−4 푢1−4 = (7) 푔휌푤푁퐻,1−4퐴퐻,1−4 where g is standard gravity on Earth, ρw is the density of water at room temperature, NH,1-4 are the numbers of holes in each radial region, and AH,1-4 are the hole areas in each radial region.
For each injector, the four calculated flow velocities go into the area-weighted flow uniformity index
4 2 ∑𝑖=1 √(푢𝑖−푢̅) ∙푁퐻,𝑖∙퐴퐻,𝑖 훾 = 1 − 4 (8) 2∙푢̅∙∑𝑖=1 푁퐻,𝑖∙퐴퐻,𝑖 where 푢̅ is the mean flow velocity.
Flow Test Equipment
PETS-II was built in-house by the Lunar Lion Team and pressurizes the flow used to test the injector designs for this experiment. The test stand repurposed several parts from Puma, the team’s first vertical flight vehicle. Appendix A shows a plumbing and instrumentation diagram
(P&ID) of this test stand for reference. A 5000 psi nitrogen bottle provides the pressure used to run the stand, and regulators step down to a safe operating pressure. A pneumatically-actuated 22 three-way valve, PA-S, opens to allow flow to the injector and closes to stop it. Figure 15 shows the test stand set up in the lab for flow testing.
\
Figure 15: PETS-II Test samples used for flow testing were 3D-printed with nylon using the Selective Laser
Sintering (SLS) additive manufacturing process. Xometry in Gaithersburg, Maryland manufactured all 3D-printed parts used for this thesis. Nylon provides good strength and stiffness, and the SLS process yields watertight prints. The flow diverters used for measuring the flow profiles are 3D-printed with the same process. Since SLS 3D printing is powder-based and does not require supports, complex geometries are easily printable. The diverters collect flow from certain regions of the injector and reduce down it to the size of standard aluminum tubes that slide into a holder. Figure set 16 shows cutaway views of the SolidWorks assemblies for the three diverters. 23
Figures 16a-c: Flow diverters for flow bounded by the outer limits of regions 1, 2, and 3 24 The aluminum tubes connect to flexible PVC tubes that connect to plastic jugs. Having a continuous connection between the diverter and the collection jug ensures that no flow outside of the desired region will enter the container. Figure 17 shows the entire diverter assembly configured for flow region 1.
Figure 17: Flow diverter setup A digital food scale is used to weigh the water collected for all flow tests, and for total weight flow, a plastic container collects the flow. For flow profile tests, a pan is placed under the flow diverters for the flow not collected by a diverter. 25
Chapter 5
DATA ANALYSIS AND RESULTS
Data Analysis
All data analysis is performed in an Excel spreadsheet, which uses the equations from
Chapter 4 to calculate total weight flow, velocity profiles, and flow uniformity coefficients.
Figure 18: Data analysis spreadsheet example
Flow Test Results
Testing was delayed due to setbacks when building PETS-II, so only Injector Design 0 and
Injector Design 1 were tested before submission of this thesis. Injector Design 0 was tested first and showed flow biased toward the center of the injector. This result is confirmed by the flow velocity profile for Injector Design 0 in Fig. 19. 26
Figure 19: Injector Design 0 flow velocity profile Here, flow velocity is significantly higher for the innermost region of the injector than the outer regions. This confirms the observation that the center portion of the catalyst bed has worn faster than the outer regions due to higher flow velocity in that region. Additionally, it is clear that the
SolidWorks flow simulation results for Injector Design 0 do not accurately represent its flow pattern since simulation results predicted a more outwardly biased flow.
Despite attempting to make Injector Design 2 an improved injector design, its flow velocity profile was less uniform than Injector Design 0 as shown in Fig. 20. 27
Figure 20: Injector Design 2 flow velocity profile As predicted in the SolidWorks flow simulation performed for Injector Design 1, the conical wedge caused the flow to be heavily biased toward the center of the injector. The smaller and fewer holes in the regions 1 and 2 for Injector 2 aimed to mitigate this effect, but they did little to correct for the conical wedge.
The flow behavior for the two injector designs is directly compared by calculation of the total weight flow and flow uniformity coefficients. Table 1 shows the values calculated from the two injector designs.
Table 1: Flow test data
Injector Design Total Weight Flow (lb/s) Flow Uniformity Coefficient
0 0.422 lb/s 0.752
2 0.446 lb/s 0.512
Injector Design 2 had a total flow rate of 0.446 lb/s, which was about 6% higher than the total flow rate of 0.422 lb/s from Injector Design 0. As expected, the conical wedge slightly reduced the 28 injector’s resistance by providing a smoother transition for the flow. However, the flow through
Injector Design 2 had a uniformity coefficient of 0.512, which was 32% lower than the flow uniformity coefficient of 0.752 for Injector Design 0.
Flow test results show that Injector Design 2 is not an improvement over Injector Design
0 since it failed to produce the desired outcome of a more uniform flow. However, the calculated values show that an injector test setup manufactured from 3D-printed components can provide meaningful data to facilitate future iterations in the injector redesign process. Most notably, the flow diverters worked as planned by providing reasonable results for weight flow through different regions of the injector to calculate the flow uniformity index.
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Chapter 6
CONCLUSION
In conclusion, this thesis successfully developed a process for designing, manufacturing, and testing injector designs using additive manufacturing techniques. However, efforts to redesign the injectors used in the Penn State Lunar Lion Team’s hydrogen peroxide monopropellant thrusters have not yet yielded an injector design that improves flow uniformity, though a small increase in total flow rate through the injector was observed. SolidWorks flow simulation gave some insight on the effect of adding a conical flow diverter to the injector plate, but failed to predict injector flow scenarios. The SLS 3D-printing process produced parts suitable for flow testing at lower price and shorter lead time than traditional manufacturing methods. Water flow testing used
3D-printed flow diverters to measure weight flow through different regions of the injector designs, which generated baseline performance data for an injector design similar to what is currently in the hydrogen peroxide thrusters. This data provides a means of comparison for future efforts to redesign the injectors.
Future work should aim to continue the iterative design process outlined in this thesis.
Lunar Lion propulsion team members should continue creating injector designs until achieving a design with higher total flow rate and flow uniformity index. After creating an optimized injector design, a peroxide engine should be tested with the new injector installed to see if performance characteristics improve. If engine performance increases, optimized injectors should be integrated into all four engines used for the Lynx flight vehicle. Future injector redesign work should also aim to eliminate the need for the 1/8-inch orifices by creating an injector plate with sufficient 30 pressure drop. Flow rate measurements can be used to generate a theoretical pressure drop for a particular injector design. However, a complete injector redesign that ensures adequate pressure drop requires the study of pressure oscillations in the catalyst bed by measuring chamber pressure in the engines during engine testing. 31 Appendix A
TEST STAND P&ID
BIBLIOGRAPHY
[1] Morgan, K., “The Qualification and Acceptance Testing of Hydrogen Peroxide
Monopropellant Thrusters”, B.S. Thesis, Aerospace Engineering Dept, Penn State
Univ., University Park, PA, 2017.
[2] “Hydrogen Peroxide,” PubChem Available:
https://pubchem.ncbi.nlm.nih.gov/compound/hydrogen_peroxide.
[3] Idel’chik, I.E. and Steinbergh, M.O., Handbook of Hydraulic Resistance, 3rd ed., CRC
Press, Boca Raton, FL, 1994, pp 518.
[4] Kang, H., Kang, S., Kwon, S., and Lee, D., “Effect of H2O2 Injection Patterns on Catalyst
Bed Characteristics,” Acta Astronautica, Vol. 130, No. 1, 2017, pp. 75-83.
ACADEMIC VITA
Academic Vita of Matthew Wehner [email protected]
Education The Pennsylvania State University, Schreyer Honors College Bachelor of Science in Aerospace Engineering
Thesis Title: Injector Redesign for a Hydrogen Peroxide Monopropellant Thruster Thesis Supervisor: Rui Ni Honors Adviser: Robert Melton
Work Experience Masten Space Systems Summer Intern May 2017-August 2017 Helped test and maintain vertical takeoff, vertical landing (VTVL) rockets and related hardware
Extracurricular Activities Penn State Lunar Lion Team Propulsion Team Member, Test Technician February 2015- Present Worked on a team developing a prototype lunar lander with a hydrogen peroxide propulsion system
Penn State Student Space Programs Laboratory Structures Team Member January 2015- April 2017 Worked on the OSIRIS-3U CubeSat that was launched as an auxiliary payload on SpaceX’s CRS-12 International Space Station resupply mission
Honors and Awards Sigma Gamma Tau- Aerospace Engineering Honor Society Spring 2017-Present Richard W. Leonhard Scholarship in Aerospace Engineering 2016, 2017 The Evan Pugh Scholar Award 2016, 2017 The President Sparks Award 2016 The President’s Freshman Award 2015