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WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 1
Accelerated Burning of Gun Propellants Caused by Pressure Oscillations Within the Perforations
of Propellant Grains
Gert Pauly – Rudolf ScheibelWehrtechnische Dienststelle für Waffen und Munition (WTD 91)D-49716 Meppen, Germany email: [email protected]
43rd Annual Armament Systems:Gun & Missile Systems Conference & ExhibitionApril 21 – 24, 2008, Sheraton New Orleans Hotel
New Orleans, LA, U.S.A.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 2
Contents
1. Pressure oscillations in holes of propellant grains
2. Connections between pressure oscillations, accelerated burning and temperature behaviour
3. Working hypothesis explaining the effect of accelerated burning caused by pressure ocillations
4. Conclusions
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 3
Messkurve Treibladungsanzünder 120 mm Mörser bei STUB
-100
0
100
200
300
400
500
-5 0 5 10 15 20
Zeit in [ms]
Dru
ck in
[bar
]
Druck
Example for Vieille-oscillations in a closed vesselWTD 91 January 2007
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 4
Oscillations superimposing the rise of pressure
0 10 20 30 40t [ms]
0
200
400
600
800
1000
Dru
ck
[ba r
]
TLP Typ I5420Länge 50 mmTemp. -40°CSamplerate 12 usLadedichte 0,1 g/mlBombenvolumen 700 mlFile 27779b
Pressure / time curve resulting from burning a tube propellant in a closed vessel.The oscillations are found in the encircled range.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 5
Pressure oscillations when burning a tubular propellant
0 2 4 6 8t [ms]
0
10
20
30
-10
-20
-30
Dru
ckdi
ffere
nz
[bar
]
TLP Typ I5420Länge 50 mmTemp. -40°CSamplerate 2 usLadedichte 0,2 g/mlBombenvolumen 700 mlFile 27782b Kanal 2
Dargestellter Bereich 200 bar - 768 barbei einem Pmax der Messung von 2329 bar
The picture was achieved by subtracting the original p / t - curve from the smoothed p / t - curve.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 6
Confirmation of the existence of pressure oscillations when burning propellant grains
Final report to ISL-VE05029-1
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 7
Confirmation of the existence of pressure oscillations when burning propellant grains
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 8
Abnormal (wavelike) erosions in the holes
The picture shows a sectional view of a triple-base 19-hole-propellant grain after interrupted burning at - 46°C (- 51°F). The wavelike erosions indicate the occurrence of standing waves in the holes.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 9
Frequency spectrum of a tubular propellant with a length of 50 mm
0 30 60 90 120[kHz]0
0,6
1,2
1,8
2,4
3
Inte
nsitä
t
X=19,7 kHz
X=50,0 kHz
X=99,8 kHz
TLP Typ I5420Länge 50 mmTemp. -40°CSamplerate 2 usLadedichte 0,1 g/mlBombenvolumen 700 mlFile 27779b Kanal 2
X=10,0 kHz
Characteristic maxima of frequencies associatedwith the fundamental frequency (10 kHz)
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 11
0 10 20 30 40 50 60 70 80 90 100 110 120 130 [kHz]
00,40,81,2
00,30,60,9
00,20,40,6
00,20,40,6
00,20,40,6
0123
5 mm
10 mm
15 mm
20 mm
30 mm
50 mm
Frequency spectra of different long propellant tubes (Loading density = 0.1 g/ccm)
Length
Frequency spectra of tubular propellants with different lenghts
( Loading density = 0.1 g/ccm )
30 mm
50 mm
20mm
5 mm
10 mm
15 mm
The shift of the frequencies proves that the oscillationsare connected with the tube lengths.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 12
Contents
1. Pressure oscillations in holes of propellant grains
2. Connections between pressure oscillations, accelerated burning and temperature behaviour
3. Working hypothesis explaining the effect of accelerated burning caused by pressure ocillations
4. Conclusions
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 13
Abnormal (wavelike) erosions in the holes
The picture shows a sectional view of a triple-base 19-hole-propellant grain after interrupted burning at - 46°C (- 51°F). The wavelike erosions indicate the occurrence of standing waves in the holes.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 14
Abnormal (wavelike) erosions in the holes
Double-base 7-hole-propellant grain after interrupted burning at - 40°C (- 40°F).
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 15
19-hole-triple-base-propellantR5730
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 16
German Armored Howitzer 2000PzH 2000 , Cal. 155 mm
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 18
R5730after
Inter-rupted burning
-46 °C = -51 °F
+60 °C = +140 °F
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 19
Pressure - time curves of the propellant R5730 in a closed vessel at – 40 (- 40°F) and +50°C (+122°F)
Both curves are temporally superimposed to improve the comparability. The cold propellant (-40°C)shows intense oscillations. The warm one (+50°C) shows only weak and short-time oscillations.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 20
Pressure - time curves of the propellant R5730 in a closed vessel at – 40 (- 40°F) and +50°C (+122°F)
Furthermore the cold propellant shows increasing oscillations for a while connected with
accelerated burning and overtakes the warm propellant during burning.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 21
Pressure - time curves of the propellant R5730 in a closed vessel at – 40 (- 40°F) and +50°C (+122°F)
Having overtaken - the oscillations of the cold propellant die away and the burning rate risesslower. The burning rate of the warm propellant rises faster and overtakes the cold one again.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 22
Pressure - time curves of the propellant R5730 in a closed vessel at – 40 (- 40°F) and +50°C (+122°F)
Finally the warm propellant reaches a higher maximum pressure than the cold propellant.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 23
The excessive burning corresponds with the intensity of pressure
oscillations
Dynamic Vivacity: V = dp/dt * 1/(pmax* p(t))
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 24
Contents
1. Pressure oscillations in holes of propellant grains
2. Connections between pressure oscillations, accelerated burning and temperature behaviour
3. Working hypothesis explaining the effect of accelerated burning caused by pressure ocillations
4. Conclusions
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 25
Gas Phase Reaction Zone
Unburned Propellant
Heating Zone (solid)
Foam/Liquid Reaction Zonewith bubbles – two phases
Flue Gas
Flame Zone
Q
Simple model of a burning propellant surface
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 26
Abnormal (wavelike) erosions in the holes
The picture shows a sectional view of a triple-base 19-hole-propellant grain after interrupted burning at - 46°C (- 51°F). The wavelike erosions indicate the occurrence of standing waves in the holes.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 27
Wavelike erosion on the surface of a hole after interrupted burning, Tpropellant = 20°C (= 68°F), magnification: 200 times, sample 92/02
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 29
Surrounding liquid
Increasing static pressure
Cavitation bubble imploding closeto a fixed surface generating a jet (4)of the surrounding liquid.
1 432
Ultrasound generates cavitation bubbles in liquids
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 30
Working hypothesis
The foamy layer is stressed with intense pressure oscillations. The layer is modified by pressure oscillations comparably like ultrasonic waves impact a surface covered with a liquid.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 31
Gas Phase Reaction Zone
Unburned Propellant
Heating Zone (solid)
Foam/Liquid Reaction Zonewith bubbles – two phases
Flue Gas
Flame Zone
Q Q
The intense oscillations cause a reduced foam / liquid zone and an increased heat flux.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 32
Relationship between pressure oscillations and accelerated burning using a triple-base propellant with and without perforations
Grains without perforations
Grains with perforations
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 33
Grains without perforations
Sample 90/02
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 34
Dependency of dynamic vivacity on temperature, non-perforated propellant.
0 0,2 0,4 0,6 0,8 1p/pmax
0
0,03
0,06
dyn.
Leb
hafti
gkei
t [1/
(bar
xs)]
0
9
18
27
-9
-18
Probe 90/02Temperatur 63°C, 21°C, -40°CLadedichte 0,20 [g/cm 3]
+63°C
-40°C
+21°C
-40°C
Druckoszillation
[bar]
From +63 (+145°F) to –40°C (- 40°F) the vivacity of the non-perforated propellant decreases with temperature. No noteworthy oscillations can be observed.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 35
Grains with perforations
Sample 91/02
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 36
Dependency of dynamic vivacity on temperature,perforated propellant.
0 0,2 0,4 0,6 0,8 1p/pmax
0
0,04
0,08
0,12dy
n. L
ebha
ftigk
eit [
1/(b
arxs
)]
0
9
18
27
-9
-18
Druckoszillation
[bar]
Probe 91/02Temperatur 63°C, 21°C, -40°CLadedichte 0,20 [g/cm 3]
+63°C
-40°C+21°C
-40°C
Reversal of the temperature behaviour for the perforated propellant within the temperature range from +63 (+145°F) to - 40°C (- 40°F). The vivacity of the perforated propellant increases with temperature. The excessive burning corresponds with the intensity of pressure oscillations.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 37
Expanded p/pmax- scale of the initial range of the dynamic vivacities with graphic depiction of the related pressure oscillations at different temperatures
0 0,05 0,1 0,15 0,2 0,25p/pmax
0,04
0,08
dyn.
Leb
haft
igke
it [1
/( bar
xs)]
0
20
40
Dru
cko s
zilla
tion
[bar
] - 4
0°C
0
20
-20
Dru
ckos
z illa
tion
[ba r
] 6
3 °C
0
-20
-40
Dru
ckos
zil la
tion
[bar
] 21
°CProbe 91/02Temperatur 63°C, 21°C, -40°CLadedichte 0,20 [g/cm3]
At +63°C: only weak oscillations - regular behaviour of the dynamic vivacityAt +21°C: intense oscillations - increased dyn. viv. compared to the +63°C-curveAt –40°C: intense oscillations - significant increase of the dynamic vivacity
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 38
Conclusions
• During combustion of perforated propellant grains in closed vessels a special form of pressure oscillations is generated independent from the known Vieille-oscillations.
• These oscillations have been proven at several institutes(WTD 91, ISL, Diehl).
• The oscillations often result in accelerated burning and modify the surfaces of the perforations.
• Working hypothesis: The pressure oscillations modify the two phases reaction zone and cause a reduced foam layer and anincreased heat flux.
WTD 91 43RD NDIA Gun & Missile Systems Conference & Exhibition, New Orleans, April 2008 © 39
Aim of the work
Presently ammunition with temperature independentmuzzle velocity is under development.
This work is a foundation for understanding one ofthe principle burning mechanism of propellants used for this ammunition. Pressure oscillations in the holesof perforated propellant grains are able to increase the burning rate at low temperatures (over)compensating the reduced burning rate of the energetic material at low temperatures.