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Results from Gaseous Methane/Oxygen Mixture Testing
Reema RevelesMike Bangham, James Allen, Jairus Schwartz, Ross
Lambert, and Brendan ManganBangham Engineering Inc.
2018 International Explosives Safety Symposium & Exposition
• LOX-LNG fueled launch vehicles
– BE-4 by Blue Origin
• Advantages of LOX/LNG
– Denser than LH2 requiring smaller
tanks
– Simpler turbopump design
– Unlike RP-1 methane can be
used to self-pressurize
– Cost
• DoD Safety Standards
Introduction
Blue Origin’s BE-3 throttles during acceptance testing. Credit: Blue Origin
Energetic liquid TNT Equivalence
LO2/LH2Larger of 8 W2/3, or,
14%W, where W is total weight of LO2/LH2
LO2/RP-1 10%
2
• Establish Quantity-Distance for LOX-LNG explosions
• Expect gaseous explosion envelopes cryogenic
• Methane – oxygen gas test setup
Methane/Oxygen Unconfined
Explosion/Combustion Test Series
3
Balloon sizes
6 ft.(7 tests)
12 ft.(18 tests)
14.5 ft.(5 tests)
16 ft. (15 tests)
Methane Mixture ratios
Stoichiometric
+-5% by volume
+-10% by volume
+-15% by volume
Test Site
Probe setup top view
4
MUCTA test site
• Pressure probes
– Piezoelectronic Quartz ICP blast
pressure pencil probe
Instrumentation
5
Metal Track Assembly
Angular
Adjustment
Cable
Protection
Fig: Blast pressure pencil
probe mounting assembly
12.0 ft. diameter balloon, 37%
CH4, 63% GOX by volume
• Photron AX200 monochrome camera– Max. pixel resolution: 1024 x
1024
– Max. frame speed: 6,500 fps at 1 megapixel
– Captures the combustion flame front
Cameras
6
• Phantom v2512 colored camera – Max. pixel resolution:1280 x
800
– Max. frame rate: 25,700 fps
– Wide-angle view capturing the shock wave created from the blast
Fig: High speed
camera tower with
accompanying support
and camera
enclosures
• Long distance acoustic sensors– PCB 377C10 piezoelectric microphone
• Triaxial Accelerometers mounted inside witness object– +-500g pk PCB Piezoelectric 356A02
Instrumentation
7
CAD of witness object
mounted on the pole with
pressure probe
Triaxial accelerometer
mounted to welded stud
plate inside witness
object
SRS of 16-ft diameter
balloon CH4-GO2
blast event at 50 ft.
from COE
• Sensor arm with pressure probes mounted inside the
balloon for the last test
– PCB Piezoelectronics model 113B26 ICP pressure sensors
Instrumentation
8
Fig: CAD diagram
of Sensor arm
dimensions and
specifications
Fig: Sensor
arm after the
test
• As 𝑟 → 𝑟0, i.e. at the edge of the gas cloud 𝑂𝑃 →180𝑝𝑠𝑖
• 𝐎𝐏𝐦𝐚𝐱~ 𝟐𝟐𝟎𝐩𝐬𝐢 to account for increase with eq. ratio and 10% margin
Overpressure curve fit
9
Impulse
10
• As Impulse decays with scaled distance, it increases with
increasing mass.
• The autoignition limit on impulse needs to be verified in the
cryogenic test
Impulse = 38.05 𝑚𝐶𝐻40.37 𝑟/𝑟0
−0.86 psi − ms
Increasing mass
16 ft Methane/Oxygen Video
Flame speeds
• Flame speed is based on
speed of burning gas
outwards from the ignitor till
it reaches the balloon ~560-
600ft/s
• Subsequent detonation
around 5000-15000 ft/s
100
1000
10000
0 5 10 15
Velocity(ft/s)
Time(ms)
12-ft.slowcombustion
12-ft.detonation
100
1000
10000
0 5 10 15
Velocity(ft/s)
Time(ms)
16-ft.slowcombustion
16-ft.detonation
12
• Equivalent weight of TNT
TNT Equivalency
13
• Inaccurate
representation of
vapor cloud
explosions
Overpressure comparison
14
• In general, TNT based predictions are higher than MUCTA in
the near field, and matches the far field data.
• The discrepancy increases with increasing fuel mass
• The comparison with cryogenic explosions might reveal a
larger discrepancy
1
10
1 10
Pea
k o
ver
pre
ssu
re (
psi
)
Scaled distance, Z (ft/lb1/3)
12-ft diameter balloon
Kinney prediction
Brode prediction
Kingery-Bulmash prediction
MUCTA experiment 1
10
100
1 10
Pea
k o
ver
pre
ssure
(psi
)
Scaled distance, Z (ft/lb1/3)
16-ft diameter balloon
Kinney prediction
Brode prediction
Kingery-Bulmash prediction
MUCTA experiment
• TNT predicted impulse is only dependent on the scaled distance
• MUCTA models impulse decay with scaled distance and a simultaneous rise with increasing mass of fuel involved in the explosion
• Limiting of impulse with autoignition needs to be modeled.
Impulse comparison
15
0
10
20
30
40
50
60
0 5 10 15 20 25 30
Po
siti
ve
ph
ase
Imp
uls
e (p
si-m
s)
Scaled distance, Z (ft./lb1/3)
MUCTA exp. 12-ft.
MUCTA exp. 16-ft.
TNT based prediction
Long Distance Acoustics
• Blast shock waves decay to acoustic pressure waves at far field distances from the COE
• Overpressure and impulse models are not applicable
• Community noise and safety around test ranges are affected by blast testing.
0.5
1
1.5
2
2.5
0 5 10 15 20
Sh
ock
Mac
h N
um
ber
Distance/massCH41/3, Z (m/kg1/3)
6-ft diameter12-ft diameter16-ft diameterCurve fit 2.4Z^-0.35
• ISO 9613-1:1993 standard is used to model the acoustic decay
• High frequency content is rapidly absorbed by air, low frequency content is transmitted through longer distances and through any structures in the way.
• The waves inside the room can get amplified and cause room modes to occur- result in building damage through a resonance phenomenon similar to the amplification of sound in a drum
Low frequency propagation
17
Long Distance PCB
Microphone 1 - 861 ft
Long Distance PCB
Microphone 2 - 966 ft
SPL = -11.18ln(x) + 233.25dB
120
130
140
150
160
170
180
190
200
0 500 1000 1500 2000
So
un
d P
ress
ure
Lev
el [
dB
]
Distance from COE [ft]80
90
100
110
120
130
140
150
160
170
180
10 100 1000 10000
Sou
nd P
ress
ure
Lev
el [
dB
SP
L]
Sound Frequency [Hz]
r/r0 = 6.5 r/r0 = 10 r/r0 = 25r/r0 = 75 r/r0 = 150 r/r0 = 250
Faster decaySlower decay
OP/p0 = 6.25(r/r0)-1.29
0
0.1
0.2
0.3
0.4
0.5
0.6
0 100 200
OP
/p0
Normalized Distance from COE (r/r0)
Slower decay than blast wave
• The images from the combustion zone shows that the methane-oxygen mixture transitions from a deflagration to detonation (DDT) in most of the tests.
• This bounds the pressure to an upper limit at the edge of the gas cloud irrespective of the volume
• Overpressures decay as a power law of r/r0
• Impulse decays with r/r0 and increases with mass.
• Acoustic decay is modeled to represent community noise and safety issues.
Conclusions
18
Future Work
19
• Phase 1 – gas explosion tests to set probable envelope -completed
• Phase 2 – cryogenic explosion tests to establish final QD and compare with TNT based equivalent weights -ongoing
• Phase 3 – ground impact to establish public safety risks -TBD
• ULA Contract FA8811-16-9-0004
• Douglas Gogel, ULA
• Redstone Test Center (RTC) Huntsville, AL
Acknowledgements
20
THANK YOU
21