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Development of an O-Class Paraffin/HTPB-N2O Hybrid Rocket Motor

Propulsion TeamV. Hansen T. Edwards M. Hughes

AdvisorsA.P. Bruckner J. HermansonC. KnowlenA.T. Mattick

Sponsored By GenCorpPresented at the 2011 AIAA Pacific Northwest Technical Symposium1IntroductionOngoing development effort for:Experimental Sounding Rocket Association (ESRA)Intercollegiate Rocket Engineering Competition (IREC)Held annually in Green River Utahhttp://www.soundingrocket.org/

2Picture looks like it's in metric units.UW Hybrid Rocket Project1 quarter design, 1 quarter manufacturing and testing498/598 Special topics classProject Goal: Enter a paraffin hybrid rocket in the advanced class of the ESRA competitionAdvanced Class Competition Goal: Launch to 25,000 ft AGL with 10lb payload, recoverMinimum O-class motor required (20-40 kN-s)3Picture looks like it's in metric units.Why use Paraffin?HTPB based hybrids have low regression ratesmulti-port fuel grains required, poor volumetric efficiencyRecent advancements in hybrid propulsion at Stanford using liquefying fuels (liquid layer theory)Order of magnitude increases in regression rate Allows single port fuel grainsHybrids have environmental, safety and simplicity advantagesParaffin hybrids are competitive with RP1-LOX for orbital spaceflight4to wordy

Paraffin CaveatsSensitive manufacturing process9-12% Shrinkage makes form casting impractical, requires spin castingBrittle Structural can result in sloughingStructural additives necessary e.g Low Density Polyethylene Wax (Vybar 103), HTPBCarbon Black addition as an optical opacifier to increase heat transfer to the liquid layer

Development PlanSubscale regression rate study to test Paraffin fuels with various additivesSchedule requires rocket & motor to be scaled and begin manufacturing in parallel with subscale tests Verify motor performance with full scale static firesSystems integration of the propulsion system

Subscale Testing ResultsTotal of 27 subscale static fires w/ N2O & GOxFuel compositions tested with N2O92% 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)

8Subscale Testing ResultsOxidizer 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 dataOutliers caused by procedural errors removed from curve fit

anParaffin-N2O Karabeyoglu [1].1550.550P-N2O T.S. Lee and H.L. Tsai [2] .11460.5036HTPB-N2O Lohner et al. [3]0.1040.352Paraffin-N2O Experimental results.08210.5676

= Regression rate [mm/s] Gox = Oxidizer mass flux [kg/m2 sec]a = Regression rate coefficient [non-dimensional]n = Mass flux exponent [non-dimensional]9

N2O Tank Testing

Water flow injector test

Water flow tests used to determine injector Coefficient of discharge (0.8)Hydrostatic testingFirst weld attempt failed during hydro-test due to insufficient weld penetration Second hydro-test with revised weld geometry reached 9.65 MPa

12Convert drawing units to metricLiquid N2O Injector17-4PH 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 flowCoefficient of discharge 0.8

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Ignition System2.4 mm thick polycarbonate diaphragm (burst P > 6.894 MPa)Custom pyrotechnic fixed to hydrostatically pre-domed diaphragmKClO4 (60%) + GEII Silicone (20%) + 3 m Al (20%)Experimental regression rate: 25 mm/s Pyrotechnic ruptures diaphragm and ignites rocket motor

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Ignition System Test w/CO2Motor TestingScaling issues with spin casting full scale grain arose just prior to first testAddition of 10% HTPB allowed form castingStyrofoam mandrel dissolved with acetone post-casting88% Paraffin, 10% HTPB, 2% Carbon black

16Motor Testing (cont)4 full-scale static tests to dateTest #1Sustainer in pre-combustor burned faster than expected/ possibly detonatedCombustion chamber over pressurized to failure

17Full-scale Motor Test #1

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Full-scale Motor Test #1 (cont)19Motor Testing (cont)Combustor rebuilt with spare parts in 2 daysSustainer removed on later testsPyrotechnic on diaphragm by itself proved to be sufficient for motor ignitionTest #2 & #3Reliability/repeatability verifiedCombustor parameters, fuel load, unchangedHigh O/F ratio ~10Test #4 Demo at 6th IRECImplemented CO2 purge20Full-scale Motor Test #2 Video

21Full-scale Motor Test #4 Video

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25Motor Testing (cont)Several factors believed to have cause lower than design thrustHigh O/F ratio of ~10Flame holding Instability, possibly due to lack of step on the front of fuel grainOnset of stability coincides with front of the fuel grain burning through to the combustor wall

26condense to bulletsCombustion Chamber (as tested)Phenolic liners at pre- and post-combustor endsCotronics alumina ceramic adhesive layer inside cardboard linerGraphite nozzle (4:1 expansion ratio)

27Redo graphic and include revised designFuture workFull-scale test programX-ray diagnostic for regression rate measurementTest Grade C Phenolic motor liner for improved thermal protectionIncrease fuel load, redesign combustor layoutTest aluminized fuelImpinging injectorAchieve stable combustionSubscale motor test programTest structurally robust grain compositionsHigh accuracy calibrated Venturi oxidizer flow measurement

28Questions ?Team Website: www.sarpuw.orgReferences:[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, 24-27 May, 2009

[3] Kevin Lohner et al., Fuel Regression Rate Characterization Using a Laboratory Scale Nitrous Oxide Hybrid Propulsion System, AIAA-2006-4671, 2006.

Special thanks to the Aeronautics & Astronautics , Mechanical Engineering, Physics and Chemistry machine shops and Automobili Lamborghini ACSLContact Email: vkhansen@gmail.com29Backup Slides

31Fuel Compositions PlottedKarabeyoglu - Paraffin, 1 % Carbon black and proprietary structural additives, spun castT.S. Lee and H.L. Tsai - 50 % Paraffin, 46 % HTPB, 4 % IDPI, progressively poured and cooled then annealed for 7 days at 40C, form castExperimental test matrix - 92 % Paraffin, 6 % Vybar 103 (LDPE wax), 2 % Carbon black, spun castExperimental test 50P 50 % Paraffin, 46 % HTPB, 4 % IDPI , form cast

Ignition System Testing

Diaphragm with pyrotechnicDetermine optimal pyrotechnic composition and placementPre-domed diaphragm does not separate from pyrotechnicPyrotechnic ignites motor after diaphragm bursts 34