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ENHANCING UNDERGRADUATE EDUCATION:
DESIGN OF A GAS TURBINE LABORATORY FACILITY
Kirk E. Hiles
1111 11 11111 111111I 1 1111
Gregg W. Dixon
United States Coast Guard Academy
ABSTRACT
An undergraduate gas turbine laboratory facility was
designed and installed by four senior Mechanical Engineering
students for their capstone design project at the U. S. Coast
Guard Academy. The seniors instrumented a 65 horsepower gas
turbine auxiliary power unit from an HH-3F Pelican helicopter
and installed it in the existing engine laboratory. The objective
of this project was to provide an opportunity for engineering
students to better understand thermodynamic principles of gas
turbine operation through hands-on experimentation. The
laboratory facility was designed to allow students to determine
the performance characteristics of the T-62-16B gas turbine and
relate them to a Brayton cycle model. This paper details the
installation and instrumentation of the gas turbine, the design
of the data acquisition system, the results obtained with initial
system tests, and future experimental plans.
NOMENCLATURE
Please refer to the gas turbine cycle schematic depicted in
Figure 4.
Cp - specific heat (constant pressure)
;lc - compressor efficiency
t - turbine efficiency
LHV - lower heating value for the fuel.
ma - mass flow rate of air
mr- mass flow rate fuel (kerosene)
P1 - compressor inlet pressure
P2 - compressor outlet pressure
P3 - turbine inlet pressure
P4 - turbine outlet pressure
Q rate of energy production
T1 - compressor inlet temperature
T2 - compressor outlet temperature
T3 - turbine inlet temperature
T4 - turbine exhaust temperature
-
BACKGROUND
As their capstone Mechanical Engineering design project,
four students developed a simple yet educational laboratory
facility which is useful for demonstrating the operating
characteristics of a gas turbine. Once the laboratory facility is
complete, the gas turbine will be used in a thermodynamics
class to study the Brayton cycle by relating classroom theory to
actual operation. The Mechanical Engineering section also
intends to incorporate the gas turbine into an experimental
methods course to teach instrumentation and measurement
techniques.
The project itself began because of the initiative of two
junior Mechanical Engineering students working at the Coast
. Guard's Aviation Repair & Supply Center (AR&SC) during a
summer internship program. As a result of their hard work and
positive rapport with the Coast Guard's aviation engineering
community, they were able to secure the donation of two T-62168 small gas turbines to the Coast Guard Academy's
Engineering Department. These turbines were designed as
auxiliary power unit engines for the HH-3F Pelican helicopter.
The decommissioning of this helicopter fleet throughout the
Coast Guard made several of the APU turbines available as
surplus.
Presented at the International Gas Turbine and Aexoengine Congress & Exhibition
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SIM MEL
INJECTOR MO
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COMMENSTION 041NICR
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nut
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as
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COMMIESSOR
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MLA letTart oats
1
OUTPUT MNE
TO CLUTCH MD
SIS IMAIIMSSION
(3)
CAL PIMP CONO
Figure 1.
Compressor and Turbine Schematic
T-62-16B GAS TURBINE
The T-62-16B turbine was originally built by the Solar
Corporation which is currently owned by the Alturdyne
Corporation. The turbine produces 65 horsepower (hp) at full
load, and has a centrifugal compressor and radial inflow design
(see Fig. 1). The turbine provided auxiliary power for the HH3F helicopter when the primary engines were secured.
At the beginning of the one semester project, the students
visited a gas turbine laboratory at the Military Academy (Putko,
1994) to help envision what the final product would look like.
After their visit to West Point, the students installed the T-6216B turbine in the Academy's engine laboratory after designing
the starting, fuel/air, and exhaust systems. Following the
installation, they instrumented the turbine using a data
acquisition system to obtain the required data for the experiment
they designed. Finally, they started the turbine ensuring all
safety precautions were followed, and collected data with the
installed instrumentation. This paper describes the activities
involved in the creation of an undergraduate gas turbine
laboratory in the context of a capstone Mechanical Engineering
senior design project
installation
The gas turbine as received from the aviation repair school
was mounted on a test bed that included a small fuel tank,
hydraulic oil tank, and oil reservoir for the gear box. The
primary installation concerns facing the student design team
included a starting DC power supply, exhaust system to
connect to the existing ducting in the engine laboratory, a fire
suppression system, and remote operation capabilities to
alleviate safety and noise concerns.
Using an existing 28V DC adjustable power supply, the
design team wired the starting power using portable plugs,
circuit breakers, and a control panel. This source is necessary
to power the controls in a hydraulic accumulator used for
starting and for the ignitor which starts the combustion process.
Unfortunately, the wiring installation for the starting system
was not quite as simple as expected. The Academy received the
gas turbine test bed without any supporting documentation
from the repair school. In fact, the school had not run the
turbine for over 18 months, and could not provide a simple
wiring diagram. The students were able to resolve the wiring
problems and trace out the starting circuit with the assistance of
a qualified electrician and the HH-3F Pelican technical
publication (Technical Publication, 1965).
2
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Figure 2.
Exhaust
The starting panel, complete with alarms and gauges, was
taken from an HH-3F Pelican and initially mounted on the test
bed. In order to operate the turbine remotely from outside the
engine laboratory booth, the team had to relocate the starting
panel from the test bed. The students decided to sever the
wiring to the starting panel and use a 35 pin connector at each
end of the cable run in order to make the turbine and starting
panel portable if needed. By relocating the starting panel,
students can start and operate the turbine in a quiet, safe
environment, well shielded from possible engine casualties.
The engine laboratory booth also has an installed halon system
which is being retrofitted with an "environmentally safe"
chemical to provide fire protection. In addition, the design team
decided to run the turbine on K-1 kerosene versus the standard
JP-fuels used on board the helicopters because of fuel
availability.
The final installation problem facing the students involved
the exhaust system. The students designed and contracted for
the construction of ducting to transition from the 0.2 m (8
inch) diameter turbine exhaust to the existing 0.25 m (10 inch)
diameter exhaust duct. The design of this transition ducting
required allowing for the high exhaust temperature and velocity
associated with gas turbines. At the same time, the designers
were concerned with minimizing back pressure through a 180
degree bend required to connect into the existing exhaust ducting
(see Fig. 2). One unexpected problem involving hazardous
Ducting Connection
materials arose when the students opened the installed exhaust
duct located inside the engine booth. They discovered a 3 inch
build-up of exhaust soot from 15 years of operating the other
research engines in the laboratory. This put an immediate halt
on starting the turbine for fear the high exhaust velocity would
stir up the soot and discharge it into the atmosphere. After
many weeks of effort to contract out the required clean up
(involving everything from writing the work specification, to
finding bidders, to researching the hazardous waste disposal
requirements, obtaining funding for the cleaning, awarding the
contract, firing the lowest bidder, and finally re-awarding the
work to a qualified company) the design team was able to get
the 90 foot long exhaust duct cleaned. The exhaust cleaning
turned out to be the critical path item of this one semester
project, which ran from January to May. The hazardous
material was discovered in February, and was not removed until
the first week in May, three days before the end of the semester.
The students learned numerous invaluable real-world
engineering lessons through their efforts to overcome this
unexpected obstacle.
The completed installation is depicted in Fig. 3.
instrumentation
Concurrent with the turbine installation efforts, the team
also focused on designing instrumentation to obtain desired
3
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Figure 3.
Completed Installation (pending exhaust connection)
improvements will allow measuring this pressure directly.
Since a simplified cycle analysis assumes constant pressure
across the combustor, only the post-compressor pressure was
measured. This was obtained by tapping a pressure transducer
into the altitude compensation line that returned to the fuel
control system. The voltage source for the transducer was
located outside the engine booth to allow for remote operation
along with the starting panel and data acquisition system (DAS)
(see Fig. 5).
A Macintosh based DAS with LabVIEW software was
selected by the students to provide real-time monitoring and
immediate reduction of the data. Once again, the DAS was
located outside the engine laboratory wall to provide for safe,
quiet analysis as the students observe the turbine operation
through the safety window. Finally, a rotameter was installed
in the fuel system to measure the fuel flow rate.
Instrumentation remaining to be installed includes a pitot-static
tube flange to measure the exhaust flow rate, and a
dynamometer to obtain the power output. This equipment was
procured after the capstone design project, and is pending
installation.
temperature, pressure, fuel flow, and air flow data. Using this
information, the students would be able to provide a practical
demonstration of open Brayton cycle characteristics.
The students were able to obtain the temperatures at the
compressor inlet, compressor outlet, and the exhaust outlet
using K-type thermocouples (see Fig. 4). The K-type
thermocouple was selected considering the temperature ranges
expected for the T-62-16B gas turbine operating at 65 hp. The
design team did not attempt to measure the post-combustor
temperature because of the spatial variation and rapid fluctuation
in temperatures associated with combustion. In addition, the
expense and design difficulties involved with obtaining an
accurate temperature measurement radially and circumferentially
around the combustor convinced the students to obtain this
critical parameter analytically. This measurement would have
required the installation of numerous thermocouples and the
technical services of the manufacturer to disassemble, install,
balance, and reassemble the turbine combustor assembly. As
described later in the paper, the students expected to estimate the
post-combustor temperature from the pre-combustor
temperature and the fuel flow rate by performing an energy
balance on the combustor.
The inlet and exhaust pressures were assumed to be the
ambient pressure measured with a barometer in the engine
booth. Analyses indicated that back-pressure in the exhaust
system should not be significant, but future system
Excierimental Analysis
The objective of the experiment designed by the students
was to determine certain performance characteristics of the gas
4
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Slate 2
[Combustor /S
(1)
= Mr
. LHV
tate 3
Compressor
t
Turbine
If the mass flow rate of air, m a, were measured directly, then T3
could be calculated from the air standard model energy balance
relationship for the combustor:
Work
_p
Out
State I
Q
State 4 1/F
Figure 4. Gas Turbine Cycle
T1
T2
T4
1) 1 434
P2(=P3 )
22.4°C (72.3°F)
172.9°C (343.3°F)
281.2°C (538.2°F)
Mt
4.07x10 3 kg's (8.98x10-3 lbm/s)
(2)
Table 2 Sample Data Assuming
Constant Heat Capacity
Parameter
(Constant C)
T3
Tic
it
r103
Table 1 Sample Data Under No Load
Measured Value
ma Cp (T3 T2)
Although the students were not able to complete the
installation of the planned system for air flow measurement,
they could estimate T3 for the no-load condition. This was
done by noting that under the air standard, constant heat
capacity model, the temperature rise in the compressor would be
the same as the temperature drop in the turbine. A more
accurate analysis using a variable heat capacity for air yielded
comparable results. Values calculated from the measured values
in Table I using both constant and variable heat capacity models
are given in Table 2.
turbine, and relate them to a Brayton cycle model (Cengel,
1994). These characteristics included the net power output,
back work ratio, compressor efficiency, turbine efficiency, cycle
efficiency, and air/fuel ratio. These principles will be
incorporated into future undergraduate thermodynamics classes
to enhance the students' understanding of theoretical models for
the cycle.
Using the temperatures, pressures, and flow rate measured
at various stages of the cycle (see Instrumentation section), the
students were able to calculate many of the performance
characteristics using an air standard analysis. Unfortunately,
because of funding limitations and the short duration of a one
semester senior design project, the students were unable to
measure the air flow rate or the power output directly. The
students were able to demonstrate operation of the turbine
system under a "no-load" condition in which the turbine output
shaft drove only the reduction gears which would be used to
drive an electrical generator when the turbine is used in an
auxiliary power unit.
Typical data obtained during steady state conditions during
no-load operation is given in Table I.
Parameter
=
rale dated Value
(Variable Cc )
431.7°C (809°F)
80%
425.1°C (797 °F)
74%
74%
0.677 kg/s (1.49 'bra's)
0.666 kg/s (1.47 Ibm/s)
80%
These values are reasonable for a gas turbine of this type, but
obviously, it would be more satisfying to measure the air flow
rate and the power output directly under varying conditions to
allow consistency checks on the data. When the air flow and
power output measurement capabilities are added to the system,
all of the instrumentation will be carefully calibrated to allow
students to account for the effects of measurement errors. Also,
a more accurate calculation model taking into consideration the
changing composition of the combustion products would be
appropriate, particularly for the lower air/fuel ratios anticipated
for load conditions. The calculated air/fuel ratio for the no-load
conditions turns out to be about ten times the stoichiometric
ratio. This is much higher than would be expected under
normal operating loads, but may be reasonable considering that
the turbine speed regulator operates by adjusting the fuel flow
rate to obtain the desired speed. This high air/fuel ratio is
101.3 1cPa(14.7 psia)
335.8 Oa (48.7 psia)
The turbine inlet temperature, 1'3 can be estimated by assuming
complete combustion of the fuel and performing an energy
balance on the combustor. The rate of energy release, Q,
resulting from fuel combustion would be given by:
5
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Figure 5.
Starting Panel
and Data Acquisition System
2. Putko, M. M. & Potter, R. A., 1994, "An Applied Gas
consistent with the observed low turbine exhaust temperature,
Tit .
Turbine Laboratory for Undergraduate Thermodynamics
4 A EE Annual
Proceedings.
Students", 29_
Edmonton Alberta, Canada, Vol 2, pp. 2804-2807.
CONCLUSION
The students involved in this project considered that the
3. Technical Manual, Gas Turbine Engine Power Unit, T.O.
2G-T62T-6, Department of the Air Force, 1965.
preliminary results obtained with the limited instrumentation
they were able to install justified the effort required to convert a
"field unit" turbine into a useful system for undergraduate
laboratory investigations. Much of their efforts were devoted to
solving the myriad of practical problems encountered in trying
to make a sophisticated system both safe and functional. With
the assistance of skilled technicians, they were able to
demonstrate operation of the turbine unit and take useful data
which, although limited, was consistent with predictions of
simple Brayton cycle models. Future system additions will
increase its usefulness and make the efforts of this small group
of students a significant addition to the laboratory resources
available to other engineering students.
REFERENCES
I. cengel, Y.A. & Boles, M.A., Thermodynamics. An
EnitneeringApproach 2nd Ed., McGraw Hill, Inc., 1994, New
York, NY, p. 472.
6
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