Document
“Materials Aspects of Turboelectric Aircraft Propulsion” Presenter: Gerald Brown Coauthors: Hyun Dae Kim and James Felder Abstract: The turboelectric distributed propulsion approach for aircraft makes a contribution to all four “corners” of NASA’s Subsonic Fixed Wing trade space, reducing fuel burn, noise, emissions and field length. To achieve the system performance required for the turboelectric approach, a number of advances in materials and structures must occur. These range from improved superconducting composites to structural composites for support windings in superconducting motors at cryogenic temperatures. The rationale for turboelectric distributed propulsion and the materials research and development opportunities that it may offer are outlined.
National Aeronautics and
Space Administration
Materials Aspects of Turboelectric Aircraft Propulsion
Presenter Gerald V. Brown Position Senior Research Engineer Organization GRC Structures & Materials Div.
Coauthors Hyun Dae Kim, James Felder
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National Aeronautics and
Space Administration
Materials Aspects of Turboelectric Aircraft Propulsion
Presenter Gerald V. Brown Position Senior Research Engineer Organization .^ GRC Structures & Materials Div.
Coauthors Hyun Dae Kim, James Felder -r~`• Jt;n.
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National Aeronautics and Space Administration
The Turboelectric Approach
The turboelectric approach does not replace the turbine engines or the fans, rather it enables them to be located and optimized independently for the greatest aircraft benefit.
The incentive for higher thermodynamic and propulsive efficiencies remains.
www.nasa.gov 3 National Aeronautics and Space Administration
N3-X Distributed Turboelectric
Propulsion System
Superconducting Wing-tip mounted continuous superconducting turbogenerators www.nasa.gov National Aeronautics and Space Administration
BENEFITS
Large core engines with low TSFC Electric power from generators drive superconducting generators.
is distributed to multiple fans.
Fans fill in center body wake to reduce drag, fuel burn and Multiple motor-driven fans ingest emissions.
•'`
boundary layer & give high bypass ratio for low fuel burn and emissions.
Forward and aft fan noise Is shielded by airframe.
Low velocity core exhaust reduces noise.
ri
- Upper surface suction increases lift coefficient at TO & delays separation.
Electric power distribution to multiple fans is more efficient Small diameter core engine inlets and lighter than mechanical. High-speed core engines are acoustically treatable.
have fewer turbine stages than direct fan-drive cores.
THE TURBOELECTRIC APPROACH CONTRIBUTES TO EVERY CORNER OF THE SFW TRADE SPACE www.nasa.gov National Aeronautics and Space Administration
OUTLINE
q
Rationale for turboelectric distributed propulsion
q Turboelectric components
q Selected areas of materials needs and opportunities
• Engine materials for high thermodynamic efficiency and light weight- - an ongoing need High-temp disks, blades & coatings, etc Materials to reduce engine weight • Low-AC-loss conductors for motor and generator stators • Composite formers, structure and torque tubes for motors and generators • High-performance cryocoolers • High-performance cryogenic power converters (inverters) • Conformal liquid hydrogen tankage • Flight weight superconducting transmission lines www.nasa.gov 6 National Aeronautics and Space Administration
Higher Bypass Ratio & Boundary
Layer Ingestion Save Fuel
N2A Compared to N2A, N3 -X has:
Twice the fan area and bypass ratio (BPR 20 vs. 10)
Ingestion of center body boundary layer
10 to 20% lower fuel burn
Reduced noise from core engine and fans (FPR~1.35)
Engine-out thrust symmetry
Lower throttle-dependent pitching moment
* Thrust requirement is 30,000 lbf at aerodynamic design point of 31,000 feet, MN 0.8, ISA.
Thrust requirement is 108,000 lbf at rolling take-off condition at sea level, MN 0.25, and ISA+27.
“Turboelectric Distributed Propulsion Engine Cycle Analysis for Hybrid Wing-body Aircraft”, James L. Felder, Hyun Dae Kim and Gerald Brown, AIAA-2009-1132, presented at 47th AIAA Aerospace Sciences meeting in Orlando, FL, Jan 7, 2009.
www.nasa.gov 7 National Aeronautics and Space Administration Distributed Turboelectric Propulsion System Requires Cryogenic and Superconducting Components for Light Weight Superconducting transmission lines between generators and motors Superconducting motors i to drive propulsive fans Tur ven i superconducting generator i Cryogenic Inverter for variable speed fans Cryocooler(s) for cryogenic components The temperatures needed for superconducting machines and the cryocoolers or LH 2 to produce them are no strangers to the space side of NASA.
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Fully Superconducting Motor or Generator
Superconducting
AC stator coils
packs
Materials needs and opportunities for motors and generators: Composite formers and containment for rotor Composite torque tubes Low-loss super- or normal- conductors for stator windings www.nasa.gov 9 National Aeronautics and Space Administration Composite Rotor Formers, Structural Support and Torque Tubes • Lightweight rotor structure, centrifugal containment and torque transfer elements are needed.
• Current technology uses vacuum Cross section of four One of four rotor coil packs impregnation of coils in a metallic structure coil packs ready for structural elements • Lower density composite substitutes must have appropriate thermal expansion coefficients and good thermal conductivity • ― Torque tubes ‖ are required to transfer R q WUDQVIHU q • Power density of superconducting motors torque between cold region and warm parts and generators: with low heat leak.
• Composites and titanium compete here SOA: 6 hp/lb • High strength and stiffness but low Goal: >30 hp/lb thermal conductivity is desired for torque tubes.
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Low-AC-Loss Superconductors
q Must reduce hysteretic, coupling and eddy-current losses q Superconducting machines require fine, twisted superconductor filaments in a Low-temperature superconductor - NbTi high-resistance matrix to reduce losses q Complex fine-filament composites were developed for low-temp superconductors including some brittle inter-metallic ones q Critical current improvement always sought from flux pinning improvements q YBCO ribbon has high AC losses q MgB2 is more easily made with fine filaments and twist but requires lower q Air Force striated ribbon reduced loss, but operating temperature than YBCO*.
not enough for our need q High resistance matrix is an issue for q New ORNL wrap-around YBCO wire may MgB 2 have promise q Phase I SBIR made progress (Hyper Tech Research) q SOA filament diameter : 50 μm. Goal: < 10μm ORNL Structural, Single-crystal, Faceted Fibers (SSIFFS) (2009 IR-100 Award) * Yttrium barium copper oxide www.nasa.gov 11 National Aeronautics and Space Administration
Low-AC-Loss Normal Conductors
q High-purity, fine-filament Al composite conductors were produced by Air Force for use at LH 2 temperature* q Room temperature resistance of normal q High-frequency performance not pursued Al or Cu is too high but is two orders of q Matrix alloy (Al-Fe-Ce) constituents must magnitude lower near LH 2 temperature not diffuse into pure aluminum Conductor with 61 pure Al filaments in a q But the AC losses can be nearly as bad high-resistance Al-Fe-Ce matrix for LH 2 r as for superconductors operation (AFRL). Precursor strand for conductor with 2989 filaments.
q As for superconductors, fine, twisted filaments and a high resistance matrix are q Nanotube conductors at room required for Al or Cu operating at LH 2 temperature are under study for aircraft temperature wiring applications, but present DC resistivity is over two orders of magnitude too high for motors Carbon nanotube multifilament conductor for high frequency applications at room temperature, (SBIR for Air Force) *“The origin and future of composite aluminum conductors”, Oberly, C.E.; Ho, J.C.; IEEE Transactions on Magnetics, Volume 27, Issue 1, Jan 1991 Page(s):458 - 463 www.nasa.gov 12 National Aeronautics and Space Administration
State-of-the-Art-Breaking Cryocooler
Reverse-Brayton, Stirling and pulse-tube coolers are candidates Phase I SBIR produced preliminary design th of reverse Brayton cryocooler with 1 /6 the weight of existing coolers and no loss in efficiency (Creare) High performance recuperator is required Light-weight turbo-compressor is required Cooler SOA is 30 lb/hp-input.
Reverse Brayton refrigeration cycle Goal is 5 lb/hp-input.
Recuperator needs high lateral thermal conduction and low longitudinal conduction.
Opportunity for nanotube mats, etc?
Reverse-Brayton Reverse-Brayton warm module cold module (prelim. design) (prelim. design) Recuperator plate * Recuperator stack * * “A Recuperative Heat Exchanger for Space-Borne Turbo-Brayton Cryocoolers”, R. W. Hill, M. G. Izenson, W. B. Chen and M. V. Zagarola www.nasa.gov 13 National Aeronautics and Space Administration
Cryogenic Power Converter (Inverter)
• Changes DC electrical power to AC power for variable speed motor drive • Room temp inverters are 95% efficient with power density up to 10 hp/lb • 99.8% efficiency expected at cryogenic temperatures • Power density goal: 20 hp/lb or more Higher efficiency at low temp from: • Some cryogenic inverter work has – Lower ― on resistance ‖ been done – Faster switching • 2 kW unit to be delivered to NASA High heat transfer to cryo fluids is possible (by MTECH Laboratories, Inc.)
New semiconductors especially for cryo • Semiconductor parts for cryogenic temperatures use are selected from standard parts Passive components can be greatly improved Expansion coefficient compatibility important to avoid brittle failure www.nasa.gov 14 National Aeronautics and Space Administration
Flight-Weight Superconducting Transmission Lines
SOA numbers: 5 W/m loss, 10 kg/m Target numbers: Mass goal: 5 kg/m Terminations & interconnects may be issues Superconducting transmission lines for ground-based electric grid should be further developed for flight weight.
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Light-Weight, Conformal Liquid Hydrogen Tanks
Three ways LH 2 might be used: q Jet-fueled aircraft (1) - - Replace cryocoolers with tanked LH 2 . Use GH 2 as fuel (LH 2 : ~8% of total fuel energy) q Jet-fueled aircraft (2) - - Size cryocoolers for cruise. Tanked LH 2 for excess cooling at TO (LH 2 < 1 % of total fuel energy) Typical LH 2 Tanks Conformal LH 2 Tanks LH2-fueled aircraft - - q Portion of fuel cools cryogenic components before being burned.
(Zero Co aircraft) q Conformal tanks could use of odd-shaped volumes in hybrid wing body q No current NASA activity for aircraft in this q Available LH 2 would reduce or eliminate area cryocooler requirement q NASA carbon-fabric-reinforced composites for composite tanks reduced tank q More AC loss can be tolerated in motors permeability to He by 70%. H 2 permeability and generators data needed.
q Use of pure normal conductors and/or MgB 2 2 becomes more favorable with LH N.B. The use of LH2 is only a possible option. It is NOT required to implement turboelectric propulsion!
www.nasa.gov 16 National Aeronautics and Space Administration Ships, Trains & Cars Already Benefit From Why not Airplanes?
Hybrid Electric Power Systems Advances in materials can help make this possible.
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References
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A. Luongo, Superconductor Science & Technology, 2. ― Hybrid Wing/Body Cruise Efficient Short Take - Off and Landing Transport Concept Using Distributed Propulsion System ‖ , by Hyun Da e Kim, Q q 6\VWHP" qq E\ Gerald V. Brown, and James L. Felder, presented to the International Powered Lift Conference, London, July 22-24, 2008.
q 3. ― Turboelectric Distributed Propulsion Engine Cycle Analysis for Hybrid Wing - body Aircraft ‖ , James L. Felder, Hy un Dae Kim and Gerald .LP q DQG q q Brown, AIAA-2009-1132, presented at 47 th AIAA Aerospace Sciences meeting in Orlando, FL, Jan 7, 2009.
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