A catalyst containing reactor is being tested using a fuel-rich mixture of Jet A fuel and hot input air. The reactor product is a gaseous fuel that can be utilized in aeropropulsion gas turbine engines. Because the catalyst material is susceptible to damage from high temperature conditions, fuel-rich operating conditions are attained by introducing the fuel first into an inert gas stream in the reactor and then displacing the inert gas with reaction air. Once a desired fuel-to-air ratio is attained, only limited time is allowed for a catalyst induced reaction to occur; otherwise the inert gas is substituted for the air and the fuel flow is terminated. Because there presently is not a gas turbine combustor in which to burn the reactor product gas, the gas is combusted at the outlet of the test facility flare stack. This technique in operations has worked successfully in over 200 tests

Hulligan, David D.

Rollbuhler, R. James

English

NASA Technical Reports Server

NASA Technical Memorandum 105258
Safety Considerations in Testing a Fuel-Rich
Aeropropulsion Gas Generator
R. James Rollbuhler
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio
and
David D. Hulligan
Sverdrup Technology, Inc.
Lewis Research Center Group
Brook Park, Ohio
Prepared for the
Combustion Fundamentals and Applications Meeting
sponsored by the Combustion Institute
Nashville, Tennessee, April 21-24, 1991
NASA
https://ntrs.nasa.gov/search.jsp?R=19920007843 2020-03-17T13:05:44+00:00Z
SAFETY CONSIDERATIONS IN TESTING A FUEL-RICH AEROPROPULSION GAS GENERATOR
R. James Rollbuhler
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
David D. Hulligan
Sverdrup Technology, Inc.
Lewis Research Center Group
Brook Park, Ohio 44142
ABSTRACT/SUMMARY
A catalyst containing reactor is being tested using a fuel-rich mixture of Jet A
fuel and hot input air. The reactor product is a gaseous fuel that can be utilized
in aeropropulsion gas turbine engines. Because the catalyst material is susceptible
to damage from high temperature conditions, fuel-rich operating conditions are
attained by introducing the fuel first into an inert gas stream in the reactor and
ko	 then displacing the inert gas with reaction air. Once a desired fuel-to-air ratio is
Ln	 attained, only limited time is allowed for a catalyst induced reaction to occur;
w
	
	
otherwise the inert gas is substituted for the air and the fuel flow is terminated.
Because there presently is not a gas turbine combustor in which to burn the reactor
product gas, the gas is combusted at the outlet of the test facility flare stack.
This technique in operations has worked successfully in over 200 tests.
INTRODUCTION
One way of improving the combustion process in gas turbine combustors is to use
a gaseous, rather than a liquid, fuel in the primary combustion process. But a gas-
eous form of fuel is not ideal to carry in an aeropropulsion propulsion system. Liq-
uid fuel forms are preferred because of their high energy content per unit of storage
volume, their transportability, their handling ease and relative safety, lower costs,
and world-wide airport availability.
A technique for incorporating the best features of fuel liquid and gaseous con-
ditions for aeropropulsion applications is to gasify the liquid fuel in a reactor
which is part of the propulsion package and then inject the product gas into the pri-
mary combustion chamber. By using the right type of catalytic material in the reac-
tor, a product gas rich in hydrogen, carbon monoxide and/or light-end hydrocarbons
can be produced from a liquid hydrocarbon fuel such as Jet A. NASA laboratory bench
testing has demonstrated that this product gas can be generated at fuel-rich opera-
ting conditions without producing soot as a by-product (Ref. 1).
It is necessary to operate this gas reactor at a rich fuel-to-air input ratio so
that only enough oxygen is available to partially oxidize the hydrocarbon fuel on the
catalyst surface. Prior NASA work has shown that this can be accomplished at an
equivalence ratio of 4-8, and an equivalence ratio of 1 would be stoichiometric con-
ditions (Ref. 2). At these conditions a gaseous fuel is generated that contains 2 to
8 vol % hydrogen, 6 to 14 vol % carbon monoxide, and 4 to 5 vol % light-end hydro-
carbons; depending on the input parameters.
The chief operating difficulty with such a gas generating reactor has been how
to achieve an equivalence ratio of 4-8 without going through stoichiometric fuel-to-
air ratios during startup and shutdown conditions. In conventional gas turbine com-
bustors the starting technique is to start with a flowing air stream into which fuel
is injected in increasing quantities and, as the overall reaction equivalence ratio
increases to something less than stoichiometric, the desired operating reaction tem-
perature is attained. However, if this technique was employed to reach fuel-rich
operating conditions, the fuel and air mixture would go through stoichiometric condi-
tions, and no matter how brief a time interval this might be, high operating tempera-
tures would occur that can irreversibly damage the catalyst and/or reactor.
To avoid thermal damaging startup and shutdown conditions when operating fuel-
rich catalytic reactors, this paper presents the technique developed at NASA Lewis
Research Center. Also a technique is proposed that might be more practical for
actual aeropropulsion applications when using this gasification process.
EXPERIMENTAL APPARATUS
The principle focus of this experimental program is the investigation of differ-
ent catalyst materials and operating parameters in producing a usable fuel gas for
primary combustion applications. A simple gas generator reactor was made from stain-
less steel pipe sections, internally insulated, into which a fuel atomizing injector
and catalyst test pieces could be mounted. A schematic drawing of this rig is shown
in Fig. 1.
The test rig is located in a test facility that can supply up to 450 g combus-
tion air per second at input temperature up to 1090 K. The facility can also supply
gaseous nitrogen at the same conditions. Liquid hydrocarbon fuel (e.g., Jet A) can
be supplied up to 250 g per second at 1724 kPa pressure.
The fuel is injected into the test rig through a 19 port air-blast atomizing
injector. The injector is mounted about 45 cm upstream of the catalyst reactor
section. The reactor section contains catalyst retaining monolithic ceramic or
metallic discs. The discs are 25 to 75 mm thick and about 150 mm in diameter. The
discs have from 4 to 100 axial flow passages per square centimeter of cross-sectional
area. Up to eight discs can be installed at one time in the test rig. The disc
walls are sometimes pre-coated with some type of noble metal catalyst by the supplier
using proprietary techniques.
Rig instrumentation includes flowmeters for measuring the air, inert gas, and
fuel flowrates; pressure and temperature sensors for determining conditions before
the fuel injector, after the injector and before the reactor, and after the reactor;
and gas analyzers for determining the reactor product gas constituents.
EXPERIMENTAL PROCEDURE DISCUSSION
The major problem in conducting the testing at fuel-rich operating conditions,
is how to attain the desired fuel-to-air ratio without going through stoichiometric
maximum temperature conditions. The technique devised is to use a nitrogen gas flow
through the gas generator reactor when introducing fuel or when terminating a test.
At startup, after the desired fuel flowrate has been attained by being injected and
2
vaporized in the nitrogen gas flow, the nitrogen flow is gradually terminated as
combustion air flow starts. Both the nitrogen and air streams are at the same
temperature and pressure. Figure 2 is a flow schematic showing the procedure where
flowrates are plotted as a function of operating time. The test termination sequence
is just the reverse of the startup procedure: the air flow decreases and is replaced
with the inert nitrogen gas flow, once the air flow is terminated, then the fuel flow
into the nitrogen stream is stopped.
Also shown in Fig. 2 is the procedure for emergency shutdown in case combustion
air flow is unexpectedly lost during a test. The rig flowmeters will indicate an
increase in equivalence ratio and when the flow computer senses that the ratio is
greater than 10, then a shutdown procedure will be initiated whereby the nitrogen gas
begins flowing and the air control valve is shut, and fuel flow is then stopped.
Likewise, if the fuel flow should unexpectedly start decreasing during a test, the
equivalence ratio would start decreasing and when it became less than 3, the flow
computer will again order a shutdown procedure. During startup the former shutdown
situation is held in abeyance till the fuel and air flows are at steady-state
conditions.
EXPERIMENTAL PROCEDURE DISCUSSION
The above technique has worked successfully in over 200 tests. This is illus-
trated for a typical test in Fig. 3 where the gas temperatures at different axial
locations in the test rig are plotted as a function of operating time. The gas
stream temperatures initially are at approximately the same value with hot nitrogen
gas flow. When the fuel is injected, the temperature of the gases downstream of the
fuel injector begin to decrease as the fuel vaporizes. As the nitrogen flow is re-
placed with air flow, the catalyst reactor and downstream gas temperatures begin to
increase. Testing is carried out at steady-state input conditions till the gas tem-
peratures stabilize and gas composition has been determined.
In spite of purging the test rig for several minutes at termination of a given
test, there was residual fuel and heavy end hydrocarbons on the test reactor ele-
ments. This condition could be occurring during the shutdown procedure when the air
flow is being replaced with nitrogen flow but the fuel is still flowing through the
hot reactor. Then when the nitrogen purge is terminated and air is re-introduced
into the rig, the hydrocarbons left on the elements will react and heat up the reac-
tor, probably at stoichiometric conditions but limited mass quantities. If precau-
tions are not taken, localized reaction temperatures can exceed the noble metal
catalyst temperature limits and/or the melting point of metallic portions of the
reactor. The rig operator has to monitor the local gas temperature readings during
this switch back from nitrogen to air flow and if any localized temperature starts to
suddenly increase, switch back to nitrogen. It is a matter of switching back and
forth between the nitrogen and air flows till the residual fuel on the reactor sur-
faces has been completely oxidized without exceeding upper temperature limits.
EXPERIMENTAL PROCEDURE DISCUSSION
Another safety aspect in this testing is the disposal of the product gases gen-
erated in the test rig. Because there is presently no primary combustor in which to
completely burn the gas generator products, another technique had to be employed to
3
render them suitable for atmospheric dispersion. Safety-wise the gaseous product
could not just be vented as it was a fire hazard as well as a poison with high con-
centrations of hydrogen, carbon monoxide, and hydrocarbons.
The solution to disposing of the gases is to burn them in a commercial flare
stack. The facility test rig was connected directly into a flare stack whose burner
was about 5 meters above the test facility roof. The stack had a natural gas and air
pilot burner at its exit and this burner had to be lit before and during any testing
in the facility. The burning plume of exhaust gas during testing gave an indication
from its appearance of how the reactor was performing. Downwind gas sampling did not
indicate any dangerous levels of atmospheric pollution.
FUTURE CONSIDERATIONS
While the startup and termination procedure using a nitrogen purge has been suc-
cessfully in the current fuel-rich, catalytic reactor test program, it is not a prac-
tical technique for flight propulsion applications. It would be a burden to have to
use a secondary fluid system (i.e., nitrogen gas) every time the aircraft propulsion
system was started or shut down.
The main function of the hot nitrogen gas flow is to provide thermal energy for
vaporizing the injected liquid fuel. If the nitrogen were cold, or nonexisting, the
injected fuel would find little available energy to vaporize it and it would tend to
puddle in the generator. Then when the hot air made contact with it there would be
all levels of fuel-to-air mixture ratios in the reactor.
If the injected liquid fuel can be heated to its vaporization temperature, then
when the air is introduced it will contact a fuel vapor and there will be a uniform
transitions from an infinite equivalence ratio to a desired 4-8 ratio.
A way of imparting energy to the fuel in the injector is to surround each of the
injection feed tubes, currently there are nineteen 1 mm tubes, with a heated air
flow. The initial fuel flow might be kept low so that the available heat will vapor-
ize the fuel. The air flow can be heated in an auxiliary electric heater.
With minimum fuel flowrates the equivalence ratio will be low but with increas-
ing reactor temperature the fuel flow can be increased to achieve a safer, higher
fuel-air mixture. The auxiliary air heater need only be used for startups and shut-
downs could be accomplished by ramping the fuel off as the air flow decreases.
Presently these ideas are just concepts, but plans are being made to evaluate
them in the present test rig.
REFERENCES
1. Brabbs, T.A., and Olson, S.L., "Fuel-Rich Catalytic Combustion - The First
Stage of a Two-Stage Combustor," NASA TM-87042, 1984.
2. Brabbs, T.A., Rollbuhler, R.J., and Lezberg, E.A., "Fuel-Rich Catalytic Combustion
- A fuel Processor for High-Speed Propulsion," NASA TM-103177, 1990.
4
Atomizint
Comb Up to 450 GM/SEC
Air	 Up to 1090kUp to 250 Kpa press,
— Monolithic metallic or
ceramic honeycomb
Liquid hydrocarbon fuel	 discs. catalytically coated
Figure 1.—Fuel-rich, catalytic reactor schematic.
Gaseous products: up to
1350K, 13% hydrogen,
18% carbon monoxide,
10% light hydrocarbon
gases, and inerts
1500
1000
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OY
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1500
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Normal Startup	 Normal Shutdown
0	 100	 200	 300
	
x+0	 x+100	 x+200	 x+300
Operating time, seconds	 Operating time, seconds
x+0	 x+100	 x+200	 x+300	 x+0	 x+100	 x+200	 x+300
Operating time, seconds 	 Operating time, seconds
Figure 2.—Fuel-rich catalytic reactor flow sequencing vs. operating time where x = finite time after starting a given test.
6
60	 1100
50	 1000
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100	 150	 200
	
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70	 1200
10	 600
0	 500 L
Light end hydrocarbons in the exhaust
1-------------------
I
1
Fuel on Air on I
11 	
1
	
^	 Post catalyst gas temperature1
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Figure 3.—Fuel-rich catalytic reaction program flow system gas temperatures and exhaust gas conc.
7
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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED
1991 Technical Memorandum
4. TITLE AND SUBTITLE 5. FUNDING NUMBERS
Safety Considerations in Testing a Fuel-Rich Aeropropulsion Gas Generator
WU-537-02-206. AUTHOR(S)
R. James Rollbuhler and David D. Halligan
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
REPORT NUMBER
National Aeronautics and Space Administration
Lewis Research Center E-5976
Cleveland, Ohio 44135 - 3191
9. SPONSORING/MONITORING AGENCY NAMES(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING
AGENCY REPORT NUMBER
National Aeronautics and Space Administration
Washington, D.C. 20546- 000 1 NASA TM-105258
11. SUPPLEMENTARY NOTES
Prepared for the Combustion Fundamentals and Applications Meeting sponsored by the Combustion Institute, Nashville, Tennessee,
April 21-24, 1991. R. James Rollbuhler, NASA Lewis Research Center; David D. Hulligan, Sverdrup Technology, Inc., Lewis Research
Center Group, 2001 Aerospace Parkway, Brook Park, Ohio 44142. Responsible person, David D. Hulligan, (216) 433-6629.
12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE
Unclassified - Unlimited
Subject Category 07
13. ABSTRACT (Maxirrwm 200 words)
A catalyst containing reactor is being tested using a fuel-rich mixture of Jet A fuel and hot input air. The reactor product
is a gaseous fuel that can be utilized in aeropropulsion gas turbine engines. Because the catalyst material is susceptible to
damage from high temperature conditions, fuel-rich operating conditions are attained by introducing the fuel first into an
inert gas stream in the reactor and then displacing the inert gas with reaction air. Once a desired fuel-to-air ratio is
attained, only limited time is allowed for a catalyst induced reaction to occur; otherwise the inert gas is substituted for the
air and the fuel flow is terminated. Because there presently is not a gas turbine combustor in which to burn the reactor
product gas, the gas is combusted at the outlet of the test facility flare stack. This technique in operations has worked
successfully in over 200 tests.
14. SUBJECT TERMS 15. NUMBER OF PAGES
Safety; Catalytic combustion 8
16. PRICE CODE
A02
17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT
OF REPORT OF THIS PAGE OF ABSTRACT
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Safety considerations in testing a fuel-rich aeropropulsion gas generator

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