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 secondsFigure 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]