Power Efficient and Restart capable Acrylonitrile Butadiene Styrene Arc Ignitor for Hybrid Rockets Stephen A. Whitmore, PhD, Associate Professor Daniel P. Merkley, and Nathan R. Inkley, Graduate Research Associates Mechanical and Aerospace Engineering Department Utah State University 4130 Old Main Hill, UMC 4130, Logan UT 28th Annual AIAA/USU Conference on Small Satellites SSC14-X-7 August 6, 2014 1
Introduction Additive Manufacturing has Recently Emerged as a Promising Technique for Manufacturing Hybrid Rocket Fuel Grains - Method allows very high degree of consistency in manufacturing, run-to-run burn consistency - Allows for complex embedded structures to enhance burn efficiency, increase regression rate efficiency, more compact form factor - Thermoplastic materials eliminate environmentally unsustainable iso and diiso-cyanates from curing process - Eliminates all wasted materials from manufacturing process
Introduction (2) - Fused Deposition Modeling (FDM) Whitmore, Peterson, and Eilers (Utah State) 3-D Printed Acrylonitrile Butadiene Styrene (ABS) Multiple Lab-scale tests on ABS-fuel motor systems from 4-N to 800 N! HTPB " 0.93 g/cm 3! ABS " 0.975 g/cm 3 ABS and HTPB produce nearly identical mass flows, I sp, and O/F when burned with nitrous oxide Fortus and Dimension FDM Machines at USU College of Engineering.
ABS Material Properties Inexpensive, readily-available from multiple sources Thermodynamic combustion properties very similar to HTPB High structural modulus (~40% of architectural aluminum) Low risk of grain fracture Allows reduced pressure vessel thickness Low critical temperature melting point ~110 C Melting behavior of ABS can be precisely controlled Allows tight fabrication tolerances Wide variety of shapes and form factors Potential to significantly increase regression rates and shorten motor by embedding helical flow structures Melts before vaporizing, surface film cooling keeps grain exterior cool
ABS Material Properties (2) FDM-Processed ABS has very interesting electro-static discharge properties Arcing-associated with fuel vaporization
ABS Arc Igniter Concept 6
ABS Arc Igniter Concept (2) Only Horizontally Stacked ABS Segments Exhibit Useful Arcing Properties Extruded and Machined ABS No Arc Vertically Stacked FDM-processed ABS Arc runs to ground Horizontally-Stacked ABS Grains arcing along surface with fuel pyrolysis 7
ABS Arc Igniter Concept (3) Impingement Shelf Concept w Co-Axial Injector GOX Initially Used as Oxidizer 8
Little Joe Pre-combustion Chamber-Integrated Igniter Pre-combustion chamber experimental motor designed to remove need for full-scale burns Capable of changing nozzle for modulation of chamber pressure Streamlined operations Up to 100 Ignitions on Single ABS Grain Segment 9
Little Joe Burn Test Summary 10
Integrated Motor/Ignitor Configuration Used existing motor casing Wire pass-throughs built into motor cap Igniter portion based on shelf igniter design ABS grain printed in 3 interlocking segments Can print various port geometries 75 by 350 mm grain segments built and tested 11
75 mm Motor Burn Tests 12
Nitrous Oxide Ignition Tests NO 2 vapor ignition System capable of igniting NO 2 vapor Long ignition delay at Low Chamber Pressures Requires higher chamber pressure than GOX for full ignition Practical Ignition Pressures > 450 psia Only Preliminary Testing Completed 13
Power Amplification Plasma torches produce a similar high-energy plume, but are not power efficient. ABS arc ignition presents viable low-power input alternative. Power efficiency analysis results Input: 3-5 W Output: ~50,000 W Amplification factor on order of 10 4 14
Conclusion Demonstrated push-button rapid restart capability with ABS Arc-Ignitor Up to 100 restarts on single grain segment Only Horizontally Stacked FDM-Processed material appears to exhibit useful arcing Properties Successful ignition requires initial pressure of ~25 psi for GOX, > 45 psia for N 2 O Oxidizer direct impingement Low Ignition latency (GOX), Longer Latency (N 2 O) Vacuum Ignition Appears Viable Relatively low power/energy consumption Huge output power amplification factor 15
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