3.0 Equipment Description
3.1
Full Assembly
Please see Figure 4 below for an illustration of the test apparatus. It should be noted that
this figure of the test setup only shows the schlieren setup and does not show the pressure
or electrical system. For the descriptions, sizes, and weights of all the internal
components, please see Table 1 below. Please note that only major components of the
pressure system have been listed in the table. For more detailed information about the
pressure system components, please refer to Section 3.4, Pressure/Vacuum System
Documentation and the accompanying Table 6.
In addition to taking the experiment structure onboard the aircraft, the flight crew was
looking ahead to outreach activities by taking a digital camera and a toy gyroscope
onboard.
It should be noted that this experiment was not a free float experiment.
Figure 1 - Experiment Test Apparatus
Table 1 - Internal Components
Schlieren
Component
Size [in]
8 in. diameter
1.37 in. thick
Spherical Mirrors (x2)
Mirror Mounts (x2)
Flashlamp
Focal Point interrupter (sharp edge)
Weight [lbs]
Description
5.5
24 in. focal length
10 x 12 x 4
31.94
Aluminum / Bosch
7x5x3
3x3x0.75
5.0
N/A
Hard mount to frame
Hard mount to frame
Weight (lbs)
15
15
N/A
N/A
10
N/A
N/A
Description
Sowin TFT
Dell CPU
Pulnix TMC 9700
Cohu
RCA STA-3850
N/A
Captain Cook Turbo Igniter
Electrical
Component
Flat Screen Computer Monitor
Computer
Visual Imaging CCD Camera
Schlieren Imaging CCD Camera
Amplifier
Accelerometer
Spark Igniter
Component
Methane Sample Cylinder
Nitrogen Sample Cylinder
Pulsed Flame Apparatus
Methane Gas
Nitrogen Gas
Component
Digital Camera
Gyroscope Toy
Size (in)
12x12x4
15x7x20
N/A
N/A
14x14x7
N/A
N/A
Pressure**
Size (in)
Weight
11x3.5
7.0 lbs
9x2
5.0 lbs
N/A
6.0 lbs
N/A
4.9 g
N/A
4.0 g
Size (in)
N/A
N/A
Outreach
Weight lbs)
N/A
N/A
**Please see Section 3.4 for more detailed information
Description
Swagelok (304L-HDF4-1000)
Swagelok (316L-HDF4-300)
Home built
N/A
N/A
Description
Canon Still Camera
N/A
3.1.1
Equipment Layout and Flyer Positions
Please see Figure 5 for the apparatus layout for flight on the KC-135 used for takeoff,
landing, and during parabolas. The general aircraft floor plan used for this figure was
taken from the JSC RGO TEDP document number AOD 33896, May 2002. The location
of the experiment footprint was chosen as one of the two locations on the airplane that
takes advantage of both an overboard vent manifold and a power panel. As shown in the
figure, the long axis of the apparatus is aligned with the aft-forward direction and the two
flyers were located just in front of the experiment close to the middle of the fuselage. A
stress analysis was done on the frame of this apparatus assuming the above aft-forward
orientation on the KC-135. Please see Section 3.2.7 of this report, Structural Analysis,
for the results of this analysis. Restraints for the flyers were located in the positions
marked in the figure.
3.1.2
General Apparatus Hazards
Notable hazards include the containment of methane fuel and the integration of
pressurized nitrogen and methane gas containers. The schlieren gas density imaging
system presents notable hazards regarding the two required glass spherical mirrors and
high intensity flash lamp. These hazards were minimized through the design of the
experiment and through precautions taken during experimentation. The danger of
methane escaping into the test chamber was minimized through the use of kill switches,
as well as a manual shutoff valve easily at the flyer’s disposal. In addition, each
Swagelok-purchased storage tank was charged to only 100 psi, well below the 1800 psi
maximum allowable working pressure. The high-intensity flashlamp was only used
during experimentation, was completely enclosed while in use, and placed in a location
so as to ensure that no one could look into it. For more information about the schlieren
system, please refer to Section 3.5.1.
Figure 2 - Experiment layout and flyer positions
3.2
Structure
3.2.1
Design Constraints
Several constraints were taken into consideration during the structural design phase of
our project’s development.
3.2.2
Footprint Limitation
The first item considered was the geometric footprint constraint. The structure must fit
within a 20” by 60” rectangular footprint. This constraint was motivated by the layout of
bolt anchors in the aircraft cabin floor, which is laid out in a grid of 20” squares as seen
in Figure 6. These anchor points are the only points to which our rig can be secured to
the aircraft. The structural design centered around this constraint due to its fundamental
importance in the interface between the rig and the aircraft.
Figure 3 - Aircraft Floor Schematic
3.2.3 Ergonomics
Ergonomics was also taken into consideration during the structural design. It was desired
to have the main systems (i.e. pressure and schlieren) at waist level and the computer
interface (i.e. keyboard, track-pad, and monitor) at shoulder level. It was hoped that this
layout would provide easy system operation in all g-level environments.
3.2.4
Lean Flammability Ratio
Since safety was an ever-present consideration in our design, we wanted to assure that no
combustion occurred other than that which took place within the confines of our
experiment cycle. To provide this safety, the enclosure was made large enough to allow
for the maintenance of the lean flammability ratio for methane. The Lean Flammability
Ratio will be discussed in further detail in Section 3.4.2.
3.2.5
Schlieren System Accommodation
Most schlieren systems involve long-focal-length spherical mirrors whose focal length
must be “folded” by the use of flat mirrors to reduce the size required to house the overall
system. The experiment enclosure had to be made large enough to accommodate at least
the smallest possible schlieren system.
3.2.6 G-Load Specifications
NASA’s Structural Design Requirements section provided us with a set of maximum gloads which the rig must withstand. Table 2 summarizes these g-load specifications. The
g-loads were meant to approximate possible worst-case scenarios which may put higher
than normal forces on the structure (i.e. severe turbulence, hard-landing, etc.). Figure 7
shows the orientation of the rig relative to the loading directions.
Table 2 - G Load Specifications
Direction
Forward
Aft
Down
Lateral
Up
3.2.7
G-Load [g’s]
9
3
6
2
2
Structural Analysis
A structural analysis was performed to insure that the preliminary structural design would
meet all of the g-load specifications. The analysis was performed on a simplified
structural skeleton with all doors and sheet-metal skin removed. Internal system
components were approximated as point masses attached at the centers of mass of the
appropriate structural member. For each element of the structure, a force was applied
which was equivalent to the mass of that element multiplied by the acceleration (g-load)
for the case being analyzed. ISMIS, a MatLAB Toolbox, was used to perform the
required calculations involved in this analysis. Table 3 shows the result of this analysis.
The maximum tensile stress each member can withstand (yield stress) is 250 [N/mm2],
therefore no structural member was subjected to a stress that exceeded this limit during
any of the loading configurations. Figure 7 shows the orientation of the structure relative
to the aircraft and loading directions. The stress analysis results for each load
configuration are shown in Figures 8-12. It can be seen from the table and figures that
the structure can easily withstand the maximum g-loads.
Table 3 - Stress Analysis**
Configuration Maximum Stress (N/mm2) Percent of Yield Stress
Forward
67.9
27.2%
Aft
22.6
9.0%
Down
70.9
28.4%
Lateral
41.9
16.8%
Up
23.6
9.4%
** Maximum stress any member can withstand is 250 N/mm2
Figure 4 - Structure Orientation
Figure 5 - Forward Stress Analysis (N/mm2)
Figure 6 - Aft Stress Analysis (N/mm2)
Figure 7 - Down Stress Analysis (N/mm2)
Figure 8 - Lateral Stress Analysis (N/mm2)
Figure 9 - Up Load (N/mm2)
3.2.8
Component Attachments
Aluminum straps, seen in Figure 13, used along with Velcro, were used to fasten the
electrical components to the structure. In addition, the wires were bound to the structure
with wire ties.
Figure 10 - Component-mounting straps
In Figure 13 above, two straps of different sizes are shown that were used for mounting
of hardware to the test apparatus. As shown on the right side of Figure 13, rubber has
been glued to the inner surface to minimize slippage and stress.
The straps were attached to the structure by bolts in a manner that does not allow the
component to move relative to the rig. We assumed that there would be no slippage
between the strap and the component; therefore we assumed that if the component is
subject to the aforementioned g-load specifications, that load would be transmitted
directly to the connection bolts in the form of a pure shear force. According to Bosch
specifications, the shear strength of the connection bolts is 32 N/mm2, which is many
times higher than any shear force that would be applied in any of the g-load cases.
3.2.9
Floor Attachment
There were a total of four steel bolts that mount the test apparatus to the aircraft floor.
The bolts supplied (NAS 184-6 Steel Studs) were more than adequate to support the
fraction of the load that was applied to each mount.
3.3
Electrical System
The methods that were used for the electrical components to work together and ensure
proper operation of the experiment are described in detail in this section. The experiment
requires several electrical components to be synchronized so that accurate data can be
obtained. Furthermore, the electrical system was designed to be autonomous so that the
synchronization could be achieved with minimal crew interaction, thus reducing possible
errors. Finally, the electrical system was designed with many redundant safety measures
in mind, ensuring that the researchers onboard the KC-135 would not lose power from
their experiments or be in danger of excess methane releasing into the aircraft.
3.3.1
Electrical Analysis
The interaction of the electrical components with one another is detailed in the schematic
shown below (Figure 14). The specifications for each wire, which include the maximum
current flowing through that wire and the thickness of the wire, are given in Table 4.
Table 4 shows that each wire can adequately contain the current flowing through the
wire.
Figure 11 - Schematic of Electrical System
Table 4 - Wire Specifications
Wire ID
PP
P1
P3
P4
P5
P6
P7
PC
C1
C2
D1
F
G
L
MA
MB
PR
R1
R2
S1
S2
B1
B2
VA
VB
PS
A
Description
Aircraft Power Panel
Flashlamp Power
12V DC Power Supply
Audio Amplifier Power
UPC Power
Computer Monitor
24V DC Power Supply
UPS Power to Computer
Visual Camera Power Supply to
Camera
Schlieren Imaging Camera Power
Supply to Camera
Accelerometer
Flash Processor to Flashlamp
Igniter Ground Lead
Igniter Hot Lead
Visual Camera to Switch
Schlieren Camera to Switch
24V DC Power to Gas Relays
DAQ Board to N2 Purge Relay
DAQ Board to Methane Relay
Nitrogen Purge Relay to Solenoid
Methane Fuel Relay to Solenoid
AA Battery to Igniter Relay
Igniter Relay to Igniter Switch
Visual Camera to IMAQ Board
Schlieren Camera to IMAQ Board
Audio Amplifier to Speaker
DAQ Board to Audio Amplifier
Max. Current
8.6 A
3.5 A
2.0 A
1.0 A
6.0 A
2.0 A
1.0 A
4.35 A
0.6 A
Wire Gauge
12
18
direct
18
18
18
direct
18
20
0.35 A
20
0.01 A
0.01 A
0.01 A
0.01 A
0.01 A
0.01 A
1.0 A
0.025 A
0.025 A
0.5 A
0.5 A
0.2 A
0.01 A
0.01 A
0.01 A
3.16 A
0.1 A
20
20 X 8C
20
20
20 (BNC)
20 (BNC)
18 X 2
20
20
18
18
20
20
20
20
18
18
The schematic shows that six components are grounded to the surge protector. The surge
protector attaches to the aircraft power panel to ensure zero potential difference between
the electrical components and frame of the apparatus. The loads that are carried through
the components to the surge protector are detailed in the next section and in Table 4.
In addition, it should be noted that the flashlamp we will use is not a laser, but does
produce strong pulses of light. Thus, the flashlamp is configured in such a way that the
light is not directed at anyone’s eyes. Furthermore, the flashlamp will not be turned on
until the apparatus is closed.
3.3.2 Load Table
In accordance with NASA guidelines, the load table shown below was created (Table 5).
The load table describes the electrical power drawn from each power source to verify that
the experiment will not draw more current than is available.
Table 5 - Load Tables
Power Source
Name: Power Cord A
Voltage: 115 V AC, 60 Hz
Wire Gauge: 12
Max. Outlet
Current:
Power Source
Name: AA Battery
Voltage: 1.5 V DC
Wire Gauge: 18
Max. Battery
Current:
3.3.3
20 Amps
Load Analysis
Flash Lamp
24 V DC Power Supply
12 V DC Power Supply
Amplifier
Computer UPS
Computer Monitor
Total Current Draw:
Load Analysis
Electronic Igniter
0.2 Amps
Total Current Draw:
3.5 A
1.0 A
2.0 A
1.0 A
6.0 A
2.0 A
15.5 Amps
0.16 A
0.16 Amps
Automation
It is evident from this schematic that due to the number of electrical components being
used for this experiment, having the experiment run autonomously is a necessity. The
synchronization of the components includes having the flashlamp and schlieren imaging
camera starting operation at the same time and continuing operation at the same
frequency so that the rates the flashlamp is emitting light and the camera is recording data
are equal. Furthermore, both the luminosity imaging camera and the schlieren imaging
camera must begin operation at the same initial time and frequency so that the luminosity
and schlieren images align with one another and can be used to describe the flame at the
same instant in time. The final part of the synchronization includes having the speaker
begin pulsing at the instant the cameras start recording data so that it will be known when
the pulsing is occurring.
Due to its ability to allow user-friendly control over electrical components, LabVIEW
was used to automate the experiment. LabVIEW is able to synchronize the electrical
components described in the previous paragraph, as well as collect data through Data
Acquisition (DAQ) and Image Acquisition (IMAQ) cards. For this experiment, we
acquired a DAQ card and two IMAQ cards from a generous donation by National
Instruments. The DAQ card is used to record the accelerometer data, communicate the
desired amplitude and frequency to the speaker, and control the methane and nitrogen
solenoids. On the other hand, one IMAQ card records the luminosity image data while
the other IMAQ card records the schlieren image data.
The LabVIEW interface is shown below in Figure 15. From this figure, it is seen that in
addition to controlling the electrical components of the experiment, LabVIEW also
controls many other aspects of the experiment. These include the ability to alter the
frequency and amplitude of the pulse in real-time, meaning that those parameters can
change while the flame is pulsing. In addition, the rate that the accelerometer is
recording data can be altered so that changes in gravitational acceleration can be recorded
to the desired precision. Furthermore, the LabVIEW interface allows us to have the
option to save the data so that it can be analyzed.
Figure 12 - LabVIEW interface
Moreover, the LabVIEW program was created so that when the experiment is operating,
two windows will pop up showing both the luminosity and schlieren images that are
being recorded (Figure 16). These windows allow the users to make any modifications to
the cameras, such as focusing or calibrating, in real time.
Figure 13 - LabVIEW interface during experiment operation
3.3.4
Safety
In addition to providing automation, LabVIEW provides many safety features for our
experiment. These include limiting the amount of time the methane gas will flow before
the flame is ignited. If the flame does not ignite after this time, it is assumed that
something is prohibiting the flame from igniting, so the setup should be examined for any
possible problems. In most cases where the flame does not light in the specified amount
of time, it can be assumed that the amplitude and frequency of the pulse are not allowing
a sufficient amount of methane to accumulate in the ignition area. Therefore, on the next
test run, different values for the pulse amplitude and frequency should be tried. Limiting
the ignition time ensures that if there is a problem that prohibits the flame from igniting,
excess methane will not be wasted.
Another LabVIEW safety feature includes the option to purge the system of the methane
gas before any given trial run. Purging the system ensures that the pressure lines as well
as the test chamber are free of the combustible methane gas since there is not enough
oxygen available for the gas to combust.
In the event of an emergency, there are several options available to the crew to shutdown
the experiment. The most accessible method is a master on/off kill switch located on the
exterior of the structure (Figure 17). This kill switch can easily be reached by the
crewmember operating the computer. However, if for some reason he is unable to
activate the kill switch, the other crewmember will also be able to reach it. Another
option for the crew to shutdown the experiment will be to manually turn off the surge
protector. For a closer look at the kill switch, please see Figure 18.
master kill switch
Figure 14 - Master kill switch on top of structure
If activated, either of these methods will cause both the fuel and purge solenoids to
deactivate (lose power) and move to a default state. The default state of the solenoids
will immediately close the fuel supply to extinguish the flame, and initiate flow of the
purge gas to prevent any combustion from taking place. Once the purge gas has ensured
that the test chamber is safe, the crew members can manually shut it off to preserve the
nitrogen.
In addition, if the kill switch is activated, it will turn off all the electrical components
with the exception of the CPU and monitor, which are powered by an Uninterruptible
Power Supply (UPS). The UPS is basically a battery that allows the computer to operate
without electrical power from the plane for approximately five minutes. Furthermore, the
UPS prevents data loss if there is a temporary power loss, such as a black out or brown
out. The UPS will beep if there is a power loss so that the crew members will recognize
the situation and ensure that the computer is shut off properly. Having the computer
remain active during a situation in which the kill switch must be activated cannot cause
any event that would compromise the safety of those onboard the KC-135.
LabVIEW also provides an abort option through a large “STOP EXPERIMENT” button
and “QUIT” button on the LabVIEW virtual instrument panel (Figure 15). If the
experiment is running, the “STOP EXPERIMENT” button simply closes the methane
solenoid and leaves the nitrogen solenoid in the closed position. However, the “QUIT”
button puts both solenoids in their default positions and quits the LabVIEW program.
A final safety feature links what LabVIEW perceives is the state of the solenoids (open or
close) and the actual state of the solenoids. This safety feature is an essential tool
because it ensures that the LabVIEW program is operating correctly. If there is any
ambiguity in the state that LabVIEW identifies the solenoids to be in and the actual state
of the solenoids, then the kill switch will be activated.
Linking the virtual interface with the actual event is accomplished by using Light
Emitting Diodes (LEDs) on the LabVIEW interface and on the top of the experiment
structure (Figure 18). In both cases, the red light shows the state of the fuel solenoid and
the blue LED shows the state of the purge solenoid. If the red LED is on, then the fuel
solenoid is open and the methane gas is flowing. The figure below is showing this case.
Conversely, if the red LED is off, then the solenoid is closed and the methane gas is not
flowing through the pressure lines. Likewise, if the blue LED is on, then the purge
solenoid is open and the nitrogen gas is flowing through the lines. However, if the blue
LED is off, then the purge solenoid is closed and no nitrogen is flowing through the lines.
At no point should both the red and blue LEDs be on. Should this happen, then the
experiment will be aborted. Also, if LabVIEW is operating correctly, then the LEDs on
the virtual interface should correspond exactly to those on the structure. If the LEDs do
not correspond to one another, then the kill switch will be activated.
LEDs
Figure 15 - LED states during experiment operation (fuel flow on)
3.4
Pressure/Vacuum System Documentation
The pressure system that was re-designed and flown in the 2003 RGSFOP operated
nominally and successfully demonstrated its robust design. At the conclusion of the 2002
RGSFOP in which a pulsed methane-flame was first studied by a UT Austin student
team, many lessons were learned that led to the new design for this year’s flight
campaign. Being the central system of the project, changes to the pressure system
affected the design of both the structural and electrical systems. Descriptions of all
aspects of the pressure system as well as descriptions of the changes that were
implemented are described below.
Please see Figure 19 for an AutoCAD illustration of the pressure system that was used for
design and development and Figure 20 for a photograph of the system that was
subsequently flown.
3.4.1
System Description and Fluid Quantities
For a schematic showing all pressure system components used in the final system design,
please refer to Figure 21. For descriptions of all components labeled in Figure 21, also
refer to Table 6.
A methane storage cylinder (Swagelok, model 304L-HDF4-1000) was used with a
volume of 1 liter and a pressure rating of 1800psi but was only charged to 100 psi to hold
the required 4.6 grams of fuel. For information regarding measures taken to ensure safety
in the unlikely event of gas escape, please see the next section regarding the lean
flammability limit of methane fuel. A nitrogen purge system was used to eliminate the
chance of creating a fuel-air mixture in the methane line. The purge gas was stored in a
small storage cylinder (Swagelok, model 316L-HDF4-300) with a volume of 0.33 liters
and a pressure rating of 1800 psi but was only charged to 100 psi which was more than
enough gas for the entire campaign. Pressure relief valves set at 125 psi were placed just
downstream of the gas storage cylinders so that the cylinders could not be overpressurized while being charged on the ground prior to flight. Manual shut-off valves
were placed just after the relief valves, and were then followed by pressure regulators that
reduced the pressure to 40 psi. For the methane fuel line, the next component was a
micro-metering control valve with an accompanying Vernier handle that was used to set
the desired methane flow rate. The Vernier handle allowed precise flow rates to be set
and reset to allow repeatable conditions for ground and flight testing. The next methaneline component was a solenoid valve that was computer-controlled through LabVIEW
allowing the automatic control necessary to initiate several experiments in the short time
given on each parabola on the KC135. Lastly for the Methane line, a check valve was in
place that ensured no nitrogen or air could enter the methane line or cylinder, thus again
avoiding a fuel-air mixture. For the nitrogen line, the component after the pressure
regulator was a solenoid valve that was computer-controlled through LabVIEW. At this
point, the two gas lines merge into a tee connector. Please note that all lines before the
tee connector consist of ¼” stainless steel tubing with Swagelok stainless steel fittings. A
¼” stainless steel flex tube then connects between the tee connector and an emergency
relief valve set at 4 psi installed downstream of all components and directly connected to
the PFA. The Pulsed Flame Apparatus (PFA) is not considered a pressurized vessel
because it is open to the ambient air around it. Please see below for more specific
information about the PFA.
Figure 16 - Pressure System AutoCAD Design
Figure 17 - Photograph showing actual pressure system
3.4.2
Lean Flammability Limit of Methane Fuel
It is important to note that if all methane fuel is released into the test chamber and then
the igniter is activated, there is no chance of an explosion. This is because even though
the methane will combine with the ambient air in the test chamber and form a fuel-air
mixture, combustion cannot occur because the mixture will contain less than the critical
amount of fuel. This critical limit is known as the lean flammability limit of a
combustible gas [10].
The lean flammability limit of methane fuel is 5%. If all the stored methane were to
escape into the test chamber, the gas would expand to only 7.6 liters and, given that the
volume of free space in the chamber can be conservatively estimated to be 250 liters
(total enclosure volume less the approximate volume of all inside components), it is
found that the ratio of methane fuel to total free volume would be less than the above
limit:
V (CH 4 )
7.6 Liters
≅
= 3% < 5.0%
V ( free _ space) 250 Liters
(1)
When designing the new structure in AutoCAD, it was ensured that the volume of area
around the flame experiment was large enough to meet the lean flammability limit as
explained above including a very conservative factor of safety. The entire structural
volume was found to be approximately 900 liters. The flame test area occupies the upper
half of this volume, however, the many components that have been placed around the
flame nozzle must be taken into account when doing this computation. The volume of
interest was then very conservatively estimated to be 250 liters, resulting in a
flammability limit of roughly 3 percent.
Therefore, all built-in safety measures (kill switch, purge gas, and the fact that the flame
will be operating in non-premixed mode as described above) are redundant in terms of
safety because the system will not exceed the lean flammability limit. As a result, these
measures are most useful as a monitoring tool for gas leaks or flame-extinction and will
be used to save gas in the event of fuel release.
3.4.3
Operating Procedures
Following arrival at Ellington Field, our pressure system was attached to the supply
bottles of Methane and Nitrogen. The two sample cylinders attached to the apparatus
were then charged for ground testing. Ground operation was begun by first flushing the
pressure system with nitrogen purge gas. Then the electrical system was initiated and
both computer-controlled solenoid valves were set to the “closed” position. Next, the
manual on/off valves were opened and the pressure regulator was set to 30psi. Tests
(both ground and flight) then commenced by setting the desired flow rate with the
Vernier handle and running the experiment with the computer-controlled solenoid valves.
When the test matrix was completed, the manual on/off valves were closed, all remaining
methane in the tubing was burned off, and the system was purged with nitrogen once
again to ensure that excess methane did not remain in the lines.
Figure 18 - Schematic of Pressure System
Table 6 - Pressure System Design Specifications***
Schematic
Reference
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Component
Description
Pressure
Setting
(psi)
MAWP
(psi)
Quick-Connect Stem
Methane Sample
Cylinder
Relief Valve
Manual Shutoff
Valve
Pressure Regulator
Needle Valve
CH4 Solenoid
Valve (default closed)
Check Valve
1/4” stainless steel
tubing
Stainless steel flex
tubing
Relief Valve
Pulsed Flame
Apparatus
Quick-Connect Stem
Nitrogen Sample
Cylinder
Relief Valve
Manual Shutoff
Valve
Pressure Regulator
N2 Solenoid Valve
(default- open)
N/A
112
Regulator
Setting
(psi)
250
1800
Relief
Valve
Setting
(psi)
N/A
N/A
N/A
N/A
Swagelock
Swagelock
Cert.
Test /
Calib.
Date
3/25
3/25
125
N/A
3000
2500
125
N/A
N/A
N/A
Swagelock
Swagelock
3/25
3/25
N/A
N/A
N/A
3000
3000
500
N/A
N/A
N/A
40
N/A
N/A
Victor
Swagelok
ASCORed Hat
3/25
3/25
3/25
N/A
N/A
6000
??
N/A
N/A
N/A
N/A
Hoke
Swagelok
3/25
3/25
N/A
3000
N/A
N/A
Swagelock
3/25
4
N/A
3000
N/A
4
N/A
N/A
N/A
3/25
3/25
N/A
100
250
1800
N/A
N/A
N/A
N/A
Swagelok
House
Built
Swagelock
Swagelock
125
N/A
3000
2500
125
N/A
N/A
N/A
Swagelock
Swagelock
3/25
3/25
N/A
N/A
3000
500
N/A
N/A
40
N/A
Victor
ASCORed Hat
3/25
3/25
*** Note: All fittings will be Swagelok stainless steel fittings
Built By
3/25
3/25
3.4.4
Pulsed Flame Apparatus
The Pulsed Flame Apparatus (PFA) is essentially a methane exit nozzle that is mounted
by screws to a speaker purchased at Radio Shack. It is the only home-built component
involved in the pressure system and is not considered a pressurized vessel because it is
open to ambient air. Please see Figure 22 for an AutoCAD image of the PFA.
As shown, gas enters the PFA through the fuel inlet on the right. The flow then passes
through a one-inch layer of honeycomb where it is straightened to a more uniform and
predictable flow. Then, after passing through a mesh screen that is used to eliminate
possible flame flashback, the fuel is ignited just outside of the converging nozzle at the
top. It should be noted that there is a relief valve directly connected to the inlet that is set
at 4 psi.
Methane Fuel Nozzle
Flashback Protection Screen
Flow-Straightening honeycomb
Methane Fuel inlet
Pulsing Loudspeaker
Figure 19 - Pulsed Flame Apparatus
3.4.5
Flame Ignition System
A new ignition system was implemented for the current flight campaign. In 2002, a
piezo-electric igniter was used that was directly mounted to the PFA. This igniter was
both unpredictable and poorly mounted. It failed to light the flame on several occasions
and, because of its placement, caused flow disruption as methane exited the nozzle. This
disruption caused undesirable instabilities in the flame. This year, flame-ignition was
achieved through the use of a battery-powered high voltage spark igniter generously
donated by Barbeques Galore Inc. The igniter has a variable-width spark gap enabling
flexible configuration.
The igniter assembly is mounted on a swivel arm that is manually actuated by pulling or
pushing on a cable taken from a bicycle brake system. When the cable is pulled, the
igniter swings over the nozzle exit. Once in place, a button on the igniter is depressed,
causing a continuous spark until the button is released.
3.5
Schlieren Flow Imaging System
The schlieren system consists of two spherical concave mirrors, one high-speed flash
lamp, one CCD camera with neutral density filters, and a knife-edge. Schlieren imaging
techniques can show first-order density gradients in the vertical or horizontal direction
through the test section. In our case, by placing a flame in the test section, important
visual information about the internal structure of the flame can be discerned. With this
technique the relatively “cold” methane gas can be seen pulsing up through the middle of
the hot flame. Also, the flame’s hot combustion products can be seen interacting with the
ambient air. Figure 23 shows the setup used for our schlieren system.
Figure 20 - Schlieren Imaging System Schematic
3.5.1
How schlieren works
The schlieren imaging technique utilizes the fundamentals of spherical mirror optics. If a
divergent light source (i.e. point source) is placed at the focal point of a spherical mirror,
the spherical mirror will reflect a perfectly collimated light beam. This means that all of
the light rays are parallel (i.e. not converging nor diverging). Conversely, perfectly
collimated light is focused by a spherical mirror down to one point (i.e. the focal point of
the mirror). In addition, imperfectly collimated light (i.e. some rays are diverging, and
some are converging) will focus in the vicinity of the focal point but will not converge to
a single discrete point.
a.)
b.)
Figure 21 – Schlieren Schematic
a.) Perfectly collimated light rays throughout the test section; uniform
neutral image, b.) Collimated light is refracted by density gradients within
the flame; light, dark, and neutral regions within the image.
Figure 24a shows the test section with perfectly collimated, non-deflected light passing
through it. Figure 24b show the test section with a flame present. The density gradients
within the flame refract the parallel light rays by various amounts. Because these light
rays are no longer parallel, they do not all focus down to one point. The light rays that
are deflected downward are blocked by the knife edge, and the light rays that are
deflected upward make it past the knife edge and are recorded by the camera. This
creates an image of light, dark, and neutral regions that represent the amount in which the
collimated light was deflected by the density gradients. The intensity of the light and
dark regions suggest the severity of the density gradients within the flame.
3.5.2
Fabricated Schlieren Components
The mirror mounts consist of an 8” diameter cylindrical housing attached to a 10” by 10”
flat plate. An 8” concave spherical mirror will be secured inside the cylindrical housing
using four ¼”-20 thread per inch screws, and a ¼” steel and a ¼” rubber washer. The flat
plate backing of the mirror mounts will attach to another plate that has special profiles
that accommodate the insertion of a Bosch profile. This profile will be attached to swivel
hanger brackets that allow the profile to pivot about its longitudinal axis. This mirror
mount design allows for rotational and vertical adjustments. A schematic drawing of the
mirror mount is shown in Figure 25.
Figure 22 - Mirror Mounts