1. Development of an O-Class Paraffin/HTPB-N2O Hybrid Rocket Motor
Propulsion Team
V. Hansen T. Edwards M. Hughes
Advisors
A.P. Bruckner J. Hermanson
C. Knowlen A.T. Mattick
Sponsored By GenCorp
Presented at the AIAA
Pacific Northwest Technical Symposium

2. Introduction
Ongoing development effort for: Experimental Sounding Rocket Association (ESRA) Intercollegiate Rocket Engineering Competition (IREC) Held annually in Green River Utah

3. UW Hybrid Rocket Project
1 quarter design, 1 quarter manufacturing and testing
498/598 Special topics class
Project Goal: Enter a paraffin hybrid rocket in the advanced class of the ESRA competition
Advanced Class Competition Goal: Launch to 25,000 ft AGL with 10lb payload, recover
Minimum O-class motor required (20-40 kN-s)

4. Why use Paraffin? HTPB based hybrids have low regression rates
multi-port fuel grains required, poor volumetric efficiency
Recent advancement’s in hybrid propulsion at Stanford using liquefying fuels (liquid layer theory)
Order of magnitude increases in regression rate
Allows single port fuel grains
Hybrids have environmental, safety and simplicity advantages
Paraffin hybrids are competitive with RP1-LOX for orbital spaceflight

5. Paraffin Caveats Sensitive manufacturing process
9-12% Shrinkage makes form casting impractical, requires spin casting
Brittle Structural can result in sloughing
Structural additives necessary e.g Low Density Polyethylene Wax (Vybar 103), HTPB
Carbon Black addition as an optical opacifier to increase heat transfer to the liquid layer

6. Development Plan
Subscale regression rate study to test Paraffin fuels with various additives
Schedule requires rocket & motor to be scaled and begin manufacturing in parallel with subscale tests
Verify motor performance with full scale static fires
Systems integration of the propulsion system

8. Subscale Testing Results
Total of 27 subscale static fires w/ N2O & GOx
Fuel compositions tested with N2O
92% paraffin, 6% LDPE wax (Vybar 103), 2% carbon black (test matrix of 11 tests)
62% paraffin, 30% 3 m aluminum , 6% LDPE wax, 2% CB (2 tests)
50% paraffin, 50% HTPB (50P) (1 test)

9. Subscale Testing Results
Oxidizer mass flow calibrated across custom flow restrictor (Venturi/ANSI orifice was not used)
Space and time averaged N2O-paraffin regression rate measured and compared with published data
Outliers caused by procedural errors removed from curve fit
ṙ = Regression rate [mm/s]
Gox = Oxidizer mass flux [kg/m2 – sec]
a = Regression rate coefficient [non-dimensional]
n = Mass flux exponent [non-dimensional] a n
Paraffin-N2O Karabeyoglu [1]
.155
0.5
50P-N2O T.S. Lee and H.L. Tsai [2]
.1146
0.5036
HTPB-N2O Lohner et al. [3]
0.104
0.352
Paraffin-N2O Experimental results
.0821
0.5676

12. N2O Tank Testing
Water flow tests used to determine injector Coefficient of discharge (0.8)
Hydrostatic testing
First weld attempt failed during hydro-test due to insufficient weld penetration
Second hydro-test with revised weld geometry reached 9.65 MPa
Water flow injector test

13. Liquid N2O Injector 17-4PH Stainless Steel (62 mm O.D. x 6.4 mm thick)
Straight hole reamed orifices (11 or 13 holes x 2 mm dia.)
1.5kg/s LN2O mass flow
Coefficient of discharge 0.8

14. Ignition System
2.4 mm thick polycarbonate diaphragm (burst P > MPa)
Custom pyrotechnic fixed to hydrostatically pre-domed diaphragm
KClO4 (60%) + GEII Silicone (20%) + 3 m Al (20%)
Experimental regression rate: 25 mm/s
Pyrotechnic ruptures diaphragm and ignites rocket motor

15. Ignition System Test w/CO2

16. Motor Testing
Scaling issues with spin casting full scale grain arose just prior to first test
Addition of 10% HTPB allowed form casting
Styrofoam mandrel dissolved with acetone post-casting
88% Paraffin, 10% HTPB, 2% Carbon black

17. Motor Testing (cont) 4 full-scale static tests to date Test #1
Sustainer in pre-combustor burned faster than expected/ possibly detonated
Combustion chamber over pressurized to failure

18. Full-scale Motor Test #1

19. Full-scale Motor Test #1 (cont)

20. Motor Testing (cont) Test #2 & #3 Test #4 Demo at 6th IREC
Combustor rebuilt with spare parts in 2 days
Sustainer removed on later tests
Pyrotechnic on diaphragm by itself proved to be sufficient for motor ignition
Test #2 & #3
Reliability/repeatability verified
Combustor parameters, fuel load, unchanged
High O/F ratio ~10
Test #4 Demo at 6th IREC
Implemented CO2 purge

21. Full-scale Motor Test #2 Video

22. Full-scale Motor Test #4 Video

26. Motor Testing (cont)
Several factors believed to have cause lower than design thrust
High O/F ratio of ~10
Flame holding Instability, possibly due to lack of step on the front of fuel grain
Onset of stability coincides with front of the fuel grain burning through to the combustor wall

27. Combustion Chamber (as tested)
Phenolic liners at pre- and post-combustor ends
Cotronics alumina ceramic adhesive layer inside cardboard liner
Graphite nozzle (4:1 expansion ratio)

28. Future work Full-scale test program Subscale motor test program
X-ray diagnostic for regression rate measurement
Test Grade C Phenolic motor liner for improved thermal protection
Increase fuel load, redesign combustor layout
Test aluminized fuel
Impinging injector
Achieve stable combustion
Subscale motor test program
Test structurally robust grain compositions
High accuracy calibrated Venturi oxidizer flow measurement

29. Questions ?
References:
[1] Karabeyoglu, M.A., Zilliac, G., Castellucci, P., Urbanczyk, P., Stevens, J., Inalhan, G., and Cantwell, B.J. “Development of High-Burning-Rate Hybrid-Rocket-Fuel Flight Demonstrators” 39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Huntsville, AL, July 2003.
[2] T.S. Lee and H.L. Tsai, “Fuel Regression Rate in a Paraffin-HTPB Nitrous Oxide Hybrid Rocket,” 7th Asia-Pacific Conference on Combustion, National Taiwan University, Taipei, Taiwan, May, 2009
[3] Kevin Lohner et al., “Fuel Regression Rate Characterization Using a Laboratory Scale Nitrous Oxide Hybrid Propulsion System,” AIAA , 2006.
Special thanks to the Aeronautics & Astronautics , Mechanical Engineering, Physics and Chemistry machine shops and Automobili Lamborghini ACSL
Contact
Team Website:

30. Backup Slides

32. Fuel Compositions Plotted
Karabeyoglu - Paraffin, 1 % Carbon black and proprietary structural additives, spun cast
T.S. Lee and H.L. Tsai % Paraffin, 46 % HTPB, 4 % IDPI, progressively poured and cooled then annealed for 7 days at 40C, form cast
Experimental test matrix - 92 % Paraffin, 6 % Vybar 103 (LDPE wax), 2 % Carbon black, spun cast
Experimental test 50P – 50 % Paraffin, 46 % HTPB, 4 % IDPI , form cast

34. Ignition System Testing
Diaphragm with pyrotechnic
Determine optimal pyrotechnic composition and placement
Pre-domed diaphragm does not separate from pyrotechnic
Pyrotechnic ignites motor after diaphragm bursts