The study developed preliminary design concepts for the exploitation of the properties of LH2 in a turbofan engine intended for air transport use, and showed the benefits which accrue in reduction of aircraf direct operating cost. Design concepts for the engine fuel delivery and control system, including the engine high pressure fuel pump, were developed, and general concept feasibility was shown. For both the engine and the fuel delivery and control system, recommendations were made for the advanced development which is necessary to bring the technology to a state of readiness for design application. The study was of necessity abbreviated in nature: more intensive study of both the engine and fuel delivery and control system is recommended

Riple, J. C.

English

NASA Technical Reports Server

N92"21529
H2-FUELED HIGH-BYPASS TURBOFAN
J. C. K/ple
AiResearch Los Angeles D/vision
INTRODUCTION Torrance, CA 90509-2960
In 1976-77, the AiResearch Divisions of The Garrett Corporation," under contract
to the Lockheed-California Company, participated as team members in an effort to eval-
uate the potential of hydrogen fueled transport aircraft. The work was sponsored by
the National Aeronautics and Space Administration, Langley Research Center, and is
reported in full in the investigation final report, Brewe:.
AiResearch developed design concepts and the preliminary design of a LH2
fueled turbofan engine and of the significant components of the engine fuel delivery and
control system. The resulting data were used in the assessment of technical feasibility,
size, weight, performance, and direct operating cost. Also, the development which
would be required to bring this technology to a state of readiness for design application
was defined.
The studies made extensive use of previous work by Lockheed, in which various
configurations of LHz fueled transports were investigated, Brewer z. For the present
study, the subject aircraft was a 400 passenger. Mach 0.85 transport, having a range of
5500 nautical miles. This particular aircraft is described in greater detail by Brewe:.
ENGINE STUDIES
Engine studies were performed to establish a viable baseline concept for the tur-
bofan engine for a LH2 fueled transport and to assess technical feasibility and impact on
aircraft direct operating cost. The investigation phases included:
Feasibility investigation of various schemes to exploit the special properties
of hydrogen, particularly the heat sink capacity.
Parametric studies to select cycle variables and the engine configuration
which minimized direct operating cost. The factors considered in evaluating
direct operating cost were specific fuel consumption and engine weight.
Detailed definition of the selected engine design; including determining en-
gine performance throughout the flight envetope, weight and geometry, scal-
ing laws, engine estimated cost, noise and emission levels, and operating
limits and capabilities.
• Assessment of technology development required.
Hydrogen Exploitation
A study was made to determine how the unique properties of hydrogen could be
exploited to provide engine performance and/or weight benefits. The concepts which
were evaluated are shown schematically on t_e attached figure. The approach used
* Now divisions of the Allied-Signal Aerospace Company
15-I
https://ntrs.nasa.gov/search.jsp?R=19920012286 2020-03-17T13:11:25+00:00Z
was to select a turbofan cycle compatible with the aircraft requirements and to investi-
gate the effects of the selected concepts on this baseline. Previous Lockheed work,
Brewer 2, resulted in the definition of a turbofan cycle for a liquid hydrogen-fueled trans-
port, and this cycle was used as a baseline for the hydrogen exploitation feasibility
studies.
A summary of the results of the hydrogen exploitation study is included in the at-
tached table. The concepts which yield the largest reduction in DOC are fuel heating
and the expander cycle. The fuel heating concept was selected as it is less complex
and provides an equal DOC benefit. Hydrogen cooling of the turbine cooling air is also
attractive and offers advantages if higher turbine inlet temperatures are selected.
Cycle Definition and Configuration Studies
The cycle definition and configuration studies were accomplished in three phases:
A review of recent studies of advanced turbofan engines, references 3, 4, 5,
to identify and confirm the state-of-the-art, and to establish the technology
level expected to be available in the 1990-1995 time period.
Selection of a preliminary cycle for the LH_, fueled turbo fan engine, based
upon the results of the first phase study, plus other inputs.
Optimization of the preliminary cycle based upon trade-off studies, including
special consideration of a high temperature, high pressure ratio cycle.:
The final cycle selected as a result of the hydrogen exploitation studies and cyde
selection investigations has the following sign_cant features at the engine design point
(maximum cruise power, 10 668 m (35 000 ft) M 0.85):
• Fan pressure ratio of 1.7:1 and a bypass ratio of 10:1
• A booster pressure ratio of 1.45:1
• A compressor pressure ratio of 16.5:1
A rotor inlet temperature of 1379"C (2514"F) [1482°C (2700°F) maximum
rotor inlet temperature ]
• A cycle pressure ratio of 40:1
The selected engine is a twin spool, direct drive, separately exhausted turbofan.
A single stage fan and two booster stages are driven by a multistage, uncooled, axial
turbine. The gas generator consists of a 10-stage axial compressor, a through-flow cir-
cular combustor and a single-stage cooled axial turbine. The spool shafts are
concentric and the low pressure spool shaft passes through the high pressure shaft.
Four heat exchangers are included as part of the engine to provide (a) hydrogen
cooling of the turbine cooling air, (b) engine oil cooling, (c) hydrogen cooling of the
aircraft environmental control system air and (d) fuel heating.
15-2
Basic cycle and performance data are listed in the attached table.
Technology Development Required
The technology postulated for the LH2-fueled engine is representative of that
which would be incorporated in an engine entering service in the 1990 time period.
Much of the technology is not, however, unique to use of LH2 fuel and will be developed
in existing programs. Aerodynamics, materials, mechanical design and manufacturing
processes, while advanced, are equally applicable to future kerosene-fueled advanced
transport engines. However, technology development is recommended for two items
pertinent to the LH 2 fueled engine:
• Combustor
• H 2 cooling of the turbine cooling air
Combustor-Technology development is required to take advantage of the properties
of hydrogen and to execute a combustor design which is smaller, provides an improved
pattern factor, and is low in oxides of nitrogen emissions.
The design of hydrogen combustion systems is particularly amenable to analysis
relative to conventional kerosene combustion systems. The kinetic schemes and reac-
tion rates are well established except for turbulent flow. Therefore, a technology pro-
gram to develop a hydrogen combustion system would consist of analytical design
augmented by an experimental program to establish the turbulent flow kinetics and to
verify the analytical design.
H 2 cooling of turbine cooling air-There are two problems introduced when hydrogen
cooling of turbine cooling air is incorporated in an engine. The first is a design prob-
lem. Normally turbine cooling air is routed intemaUy through the engine from the com-
pressor to the cooled turbine. The routing is different when the turbine cooling air is hy-
drogen cooled. Complex design problems would have to be addressed but the task
could be best undertaken concurrently with engine design.
The second problem is caused by the lower temperature of the turbine cooling air.
Thermal gradients in the blades would be more severe than presently experienced for a
similar blade heat transfer system. These high thermal gradients can result in low cycle
fatigue damage. In order to realize the advantages of H2 cooling of the turbine cooling
air, it is recommended that parallel technology programs be undertaken to
1. Develop heat transfer systems which produce more tJniform temperatures"
2. Extend development of single crystal turbine blades which have higher cyclic
fatigue strength.
15-3
ENGINE FUEL DEUVERY AND CONTROL SYSTEM STUDIES:
Three main items were investigated:
The engine high pressure fuel pump: including preliminary definition of de-
sign requirements; identification and tradeoff study of candidate pump and
drive systems; special consideration of the pump bearing problem; and
selection of a final candidate, followed by further detailed definition.
The engine fuel control system: including preliminary definition of require-
ments; identification of candidate systems, followed by a final selection; and
preliminary consideration of engine starting and operating procedures.
The developmentwhich would be required to bring this technology to a
state of readiness for design application.
These items are illustrated in the attached figures.
Technology Development Required
The study of the engine fuel supply system identified and brought into focus vari-
ous areas of risk in the technology where advances in the state of the art are either nec-
essary or'highly desirable to facilitate the timely and economic development of a flight
system. The more significant of these items are:
-The engine high-pressure pump bearing system is a major techni-
advancedrequiring development. The current state of the art in advanced
high pressure LH2 pumps has evolved mainly from the development work which has
• been done on rocket engine turbopumps. As a result of this work, the problems of de-
signing for pump performance (head, flow range, and suction performance), and also
the problems of mechanical design and materials selection for cryogenic service, have
been adequately resolved and may be considered state of the art.
However, all rocket engine components inherently have a very short mission duty
cycle, while air transport equipment has a typical overhaul period of 5000 hours and
service life of 40,000 hours. The most critical problem in the development of a high-
pressure LHa pump suitable for airline service is the pump bearing system, and it is
recommended that the approaches described in this report be investigated.
It should be noted that these comments apply only to the bearings of the high-
pressure LH 2 pump, which are relatively highly loaded and which operate at high rota-
tional speed. The very lightly loaded bearings of a LH= fuel boost pump, which run at
lower rotational speed, can probably be developed adequately for airline service as a
further evolution of the existing design approach, using rolling element bearings and
separators having a dry lubricant capability.
Engine fuel control system-Operation of the cryogenic hydrogen fuel control system
presents several new problems such as starting with the supply line full of vapor, the
necessity for extremely rapid chill down of the engine high pressure pump, the
15-4
pl'obable necessity to control the flow of fuel in both the vapor and liquid states, and the
presence of significant volume capacitance in the fuel system combined with the use of
the relatively compressible H2 fuel. These problems make desirable analysis and com-
puter simulation of the selected engine fuel delivery and control system, followed by
fabrication and test of a breadboard system.
Overall system-It is desirable to make a preliminary investigation of systems interac-
tions involved in utilizing H2 as a heat sink for cabin air conditioning, engine oil cooling,
engine stator vane and rotor blade cooling, in combination with the engine exhaust fuel
heating concept. This may be done initially by computer simulation, and particular
attention should be paid to identifying critical off-design conditions.
CONCLUDING REMARKS
The study developed preliminary design concepts for the exploitation of the prop-
erties of LH2 in a turbofan engine intended for air transport use, and showed the bene-
fits which accrue in reduction of aircraft direct operating cost. Design concepts for the
engine fuel delivery and control system, including the engine high pressure fuel pump,
were developed and general concept feasibility was shown. For both the engine and
the fuel delivery and control system, recommendations were made for the advanced
development which is necessary to bring the technology to a state of readiness for de-
sign application. The study was of necessity abbreviated in nature: more intensive
study of both the engine and fuel delivery and control system is recommended.
REFERENCES
1". Brewer, G. D.,; et al. Study of Fuel Systems for LH2 - Fueled Subsonic Transport
Aircraft. NASA CR-145369, Final Report Contract NAS 1-14614, Lockheed -.
California Company, July 1978.
2. Brewer, G. D.,; et al. Study of the Application of Hydrogen Fuel to Long-Range
Subsonic Transport Aircraft. NASA CR-132559, Final Report Contract NAS
1-12972, Lockheed - California, January 1975.
3. Neitzel, R. E.; et al. Study of Turbofan Engine Designed for Low Energy
Consumption. NASA CR-135053, August 1976.
4. Gray, D. E.; Study of Turbofan Engines Designed for Low Energy Consumption.
NASA CR-135002, April 1976.
5. Gray, D. E.; Study of Unconventional Aircraft Engines Designed for Low Energy
Consumption. NASA CR-135065, June 1976.
6. Scott, .R.B.; Technology and Uses of Liquid Hydrogen. Oxford, New York, 1964.
7. Bierman, A. E.; and Kohl, R. C.; Preliminary Study of a Piston Pump for Cryogenic
Ruids. NASA Memorandum 3-6-59E, March 1959.
8. Bierman, A. E.; and Shinko, W. G.; Performance of a Piston Type Pump for Liquid
Hydrogen, NASA Technical Note D-276, March 1960.
9. Goldsmith, J. S.; and Bennett, G. W.; Hydrogen-Methane Fuel Control System for
Turbojet Engines. NASA-CR-121247, General Electric Company.
15-5
LH2 FUEL SYSTEM STUDY FOR
SUBSONIC TRANSPORT
PROGRAM OBJECTIVE
• EVALUATE POTENTIAL OF HYDROGEN FUELED
TRANSPORT AIRCRAFT
• SELECTION CRITERIA AIRCRAFT D.O.C., AND ENGINE
SYSTEM WEIGHT
• PARTICIPANTS
• SPONSOR: NASA LANGLEY RESEARCH CENTER
• AIRCRAFT STUDIES: LOCKHEED CALIFORNIA COMPANY
• ENGINE AND FUEL SYSTEM STUDIES:
GARRETT - AIRESEARCH
• TIME OF STUDY: 1976 - 1977
STUDY APPROACH
• ASSUME BASELINE AIRCRAFT: 400 PASSENGER, MACH 0.SS,
8800 NM RANGE
• PERFORM PARAMETRIC STUDIES OF ENGINE CYCLE VARIABLES
AND CONFIGURATION TO MINIMIZE AIRCRAFT D.O.C.
e IDENTIFY SCHEMES TO EXPLOIT LH2 PROPERTIES.
INVESTIGATE FEASIBILITY AND EFFECT ON AIRCRAFT D.O.C.
• ESTABLISH DETAILED DEFINITION OF SELECTED ENGINE
DESIGN AND PERFORMANCE
• ASSESS TECHNOLOGY DEVELOPMENT REQUIRED
15-6
CYCLE AND INSTALLED PERFORMANCE CHARACTERISTICS -
SELECTED LH2 FUELED BASELINE ENGINE
SIS. STANDARD DAY
POWER SETTING TAKEOFF
NET THRUST N, _J}
M 0.0S
10,eM, M
ps,omJr_
MAX. CRUISE
_ss_rt (so,_oe) a,loo (eM_
SFC,(k_l_N ((_/_nb) _04S (0.1US) 0_0e4 (urn4)
BYPASS RATIO 10.25 10.0
i
FAN AIRFLOW, kgJlM_ OhiO) 48:1.7 (10t8.4) 217,2 (471.8)
FANPRESSURERA_ cne) 1Jm4 1.7
'FAN PRESSURE RATIO (HUB)* 2.26 2.486
COMPRESSOR PRESSURE RATIO 18.5 IIL8
ROTOR INLET TEMPERATURE, 1482"C (2700) 131'9"C (2814)
"C, ('_
*HUll PRESSURE RATIO INCLUDES BOOSTER STAGES
INSTALLATION DRAWING - SELECTED ENGINE
ENGINE OIt. IqJiJP APT IWIDE Ikikllli INGINI WltOHf - _ POUNOI
NO]rZLES • THRt.qrl' REV|IIlUEII - m _S
TOTAL _ POUNDS
15-7
HYDROGEN EXPLOITATION CONCEPTS
imm_a
_°. %m
_t
" t . L.Q _._
I : _;J.,m..
i ............ __.
m
6. EXPAND_ CYCU[
HYDROGEN EXPLOITATION SUMMARY
¢N2
ImECOm.UmG 0.|
iNTER COmUNO 0.8
COOUB'rlE_IIINE GOOIJN8 AIR 0.8
PUEL.BOqNG 0.8
H_ lUg_mER CYCLE O.8
AP AINmC** _NE
Pm % Aw'r, KO AW'r,KO
0.041 -1.86 .-43 +76
0.04 -.0.93 -40 +100
NIA _ .-27 + 10
0.04 +118431
0.04 -431
+27
÷112
ADOC*
%
.-1.,13
.-0J7
,-0.41
-.:Ul0
-.2.9O
**RELATTVE TO THE BASEUNE SFC • 0-2042 (_)/IJ
y.Ts (AWT) + 1Jlu Sl,c -1
*DOC ('A,) - X 100
DOCu.R
15'8
LH2 ENGINE FUEL DELIVERY AND CONTROL SYSTEM
ENGINE STUDIES
ENGINE EXHAUST GAS FUEL HEATER
_H 2 IN
NO. H 2 PASSES__8
OUTSIDE DIA._____49.8 IN.
INSIDE DIA.. .22.2 IN.
LENGTH 7.6 IN
TOTAL WEIGHT__.__ 570 LIB
MATERIAL 304 CRES
TUBE O.D. 0.1118 IN
TUBE WALL 0.012 IN.
15-9
ALTERNATIVE ENGINE PUMP DRIVE CONCEPTS
m
q otuJ un IL__.-. ___ _-_ Id tPUCBBtltAlID timer ttwlol t
m
OOllram. u_tmo mlaotB NAmoq0
_mD ImlVll 8 IIBMJI
e II, N _b I_.l¢lrm¢ JOlrOet oa_ Iwlw dOVAm_BtJIt atA_ 01muir oemnlm m
LAYOUT OF ENGINE HIGH PRESSURE LH2 PUMP
me&_ Ua_url
t/ ; L'_
|iT OTA6f
15-10
REQUIRED UNIQUE TECHNOLOGY DEVELOPMENT
• COMBUSTOR DEVELOPMENT TO TAKE ADVANTAGE
OF H2 PROPERTIES
• SMALLER COMBUSTOR
• IMPROVED PATTERN FACTOR
• LOW NOx EMISSIONS
• H2 COOLING OFTHE TURBINE COOUNG AIR
• ROUTING OF H= THRU THE ENGINE TO COOL
THE TURBINE
• ADDRESS THE HIGHER THERMAL GRADIENTS
PROBLEM
• ENGINE HIGH PRESSURE FUEL PUMP
• BEARING SYSTEM
• FUEL CONTROL SYSTEM
• POTENTIAL FOR 2 PHASE FLOW
• SYSTEM VOLUME AND COMPRESSIBLE H2
CONCLUSIONS
EXPLOITATION OF H2 PROPERTIES PROVIDES
SIGNIFICANT IMPROVEMENT IN AIRCRAFT D.O.C.
AND WEIGHT
GENERAL FEASIBILITY OF THE DESIGN
CONCEPTS WAS SHOWN
REQUIRED UNIQUE TECHNOLOGY DEVELOPMENT
WAS IDENTIFIED
15-11



H2-fueled high-bypass turbofan

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