This project explored using 3D printing to optimize hybrid rocket fuel grains. ABS plastic was used as the fuel and tested with nitrous oxide oxidizer. The fuel grains were designed with different infill densities using 3D printing which allowed increased surface area over traditional casting. Two fuel grains were tested - a 90% infill design and a 25% infill design. The 25% infill grain had a higher regression rate and sustained thrust longer. Further fuel grain designs will be tested and applied to a flight-ready rocket model to analyze performance and maximize altitude within safe limits.

1. College of Engineering and Computer Science, University of Central Florida, Orlando, FL 32816, USA
3D-Printed Hybrid Rocket Fuel Grains
Fused Layer Acrylonitrile Butadiene Styrene Rocketry Experiment (F.L.A.R.E.)
Amy Besio, Jonathan Benson, Richard Horta, Joshua Rou, John Seligson
Faculty/Technical Advisor: Justin Karl, Ph.D.
Introduction Testing Apparatus Flight Ready Model
Results and Conclusions
Future Testing
Acknowledgements
Application
This project explored utilizing fused deposition modeling
(FDM) for optimization of hybrid rocket fuel grains. FDM
allowed for custom tailoring of fuel grain geometries, in order
to target desirable performance characteristics unobtainable
through traditional manufacturing. The solid propellant was
composed of acrylonitrile butadiene styrene (ABS), a common
additive manufacturing material. When exposed to an oxidizer,
ABS performs comparably to commercially available
hydroxyl-terminated polybutadiene (HTPB) fuel grains. The
liquid propellant was nitrous oxide (N2O) and provided the
oxygen content to the fuel. The scope of this project included
design, manufacturing, testing, and data review of the fuel
grains. Development of the grains entailed forming appropriate
mathematical models for solid and liquid propellant
characterization. Manufacturing encompassed fabrication of
the ABS grains using FDM and assembly of test bed
components, which includes the test stand, thrust chamber, and
data acquisition and processing. Testing consisted of a baseline
run, followed by subsequent test fires. Data review includes the
testing analysis and a comparison with computational
prediction. Several fuel grains tested in this project will be
applied to a flight ready model for performance analysis.
The proposed solution is to optimize the exposed surface
area of hybrid rocket fuel grains through the use of FDM,
commonly referred to as 3D printing. 3D printing offers
advantages unobtainable through traditional casting
methods. The precision of 3D printing provides greater
uniformity in fuel grain structure, while streamlining the
production process. The material chosen to compose the fuel
grain is ABS. It is a widely used 3D printing material and
burns intensely when ignited in the presence of an oxidizer.
The test stand was built to be compatible with varying sizes of
combustion chambers. Subsequent hybrid rocket motor tests
can be run using the test apparatus. Other geometries including
varying cross-section and infill can be tested using this
apparatus, providing valuable information on how surface area
affects hybrid fuel grain performance.
Testing System
 Rails Angled 45 Degrees
 Superstrut Platform and Clamps
 Fabrication
 Cutting, Grinding, Deburring
 Milling
 Drilling
 Welding
 Coating
 Instrumentation Integration
 Button Load Cell
 Pressure Transducers
 External Instrument
 IR Meter
Ground Test Article
 Design Considerations
 Combustion Chamber
 6061-T6 Aluminum
 54 mm X 160 mm
 Nozzle
 Ideally expanded
Pe=Pa
 Expected Performance
 Mass Flow Rate
 0.282 kg/s
 Force
 670 N
 Specific Impulse
 242 seconds
Figure 4: Instrumentation Setup
Figure 3: Exploded Test Stand
Figure 1: Future Grain Geometries Via FDM
Figure 2: Varying Infill Percentage
Figure 5: Combustion Chamber
Figure 6: Nozzle Dimensions
Figure 7: Pressure Test
Table 1: Performance of Testing System A test stand was fabricated to constrain
the test article and incorporate the
oxidizer feed system and measurement
devices. The test stand and ground test
article were overdesigned with a factor
The 90% infill standard core fuel grain was tested first. Thrust peaked at
approximately 441.5 N but dropped off significantly over the course of the
burn. Based on mass flow rate of oxidizer and fuel, a high O/F of 20.34 was
determined, which is greater than the theoretical O/F of 7.8. The 25% infill
standard core fuel grain was tested second and provided a significantly higher
regression rate. Thrust peaked at 460.0 N and was sustained longer than the
90% infill. The O/F for the 25% infill was determined to be 9.63. Combustion
chamber pressure was similar for both test runs. The 25% infill test proves the
viability of increasing surface area to improve regression rate and influence
thrust profiles.
 Type of Motor - Contrial J-245
 2000m Expected Altitude
 644 Ns Total Impulse
 3 s Burn Time
 Flight Mechanics Design
Considerations
 Fins - CP Aft of CG
 Nose Cone – Rounded Curve
 Testing of Remaining Fuel
Grains
 90% Infill
 25% Infill
 Variable Infill
The ABS fuel grains will be applied to the flight vehicle
comparable in size to a large amateur rocket. Maximum
altitude will be limited to 2000 m to allow for testing at a local
NAR site. Once all components
Figure 8: Testing of 90% Infill
(Top) and 25% Infill (Bottom)
Figure 9: Post Combustion Grains
90% (Top) and 25% (Bottom)
Figure 10: Thrust Profile of 90% and 25% Infill
Table 2: Performance of 90% and 25% Infill
Table 3: Flight Ready Instrumentation
of safety of 5 and 2 respectively, to prevent failure and allow for multiple reloads. Two nozzles
and multiple o-rings were available in order to ensure reliability for each test. The system was
tested at high pressure with solid fuel to ensure functionality and safety.
are assembled and center of
mass is determined, fin design
will be finalized to locate
center of pressure aft of the
center of mass. Three fuel
grains will be applied to this
model while measurement
instruments in table 3 will
record the environment
experienced by the rocket.
Figure 11: Flight Vehicle Center
of Gravity [Peterson]