S. A. Weckert and T. W. Joyner- Diagnostic Imaging of Detonation Waves for Waveshaper Development
IX. Detonation Waves
Transcript of IX. Detonation Waves
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6/20/2007 Detonation 5
Chemical kinetics is initiated behind the shockwave
In connection with the problem of the process of the chemical
reaction in a detonation wave, the objections raised against theconceptions of Le Chatelier and Vieille of the 19th century with regardto the ignition of the gas by the shock wave are refuted. Ya. B.Zeldovich On the theory of the propagation of detonation in gaseoussystems JETP 1940
Ya. B. Zeldovich 1940
J. H. von Neumann 1942
W. Dring 1943
Detonation as a shock-initiated,
convected explosion of combined
chain-thermal nature
6/20/2007 Detonation 6
Wave Speed is Determined by Thermodynamics
CJ Hypothesis:
1. Wave travels at slowest possible speed consistent with themodynamics
2. Product velocity relative to wave is sonic (= sound speed)
Physical explanation:Expansion waves catch up to wave and slow it down until CJ state is reached.
6/20/2007 Detonation 7 6/20/2007 Detonation 8
Steady Reaction Zone
lawratekineticbygiven:
where
21
2
1
1
,,12
2
2
i
Ye
N
i i
i
i
i
ik
YP
c
dx
dYu
M
u
dx
dPu
M
u
dx
duu
Mdx
du
C2H4
CO2
H2O
CO
C2H4-3O2-9N2, 20kPa Warnatz
OH
H
O
Convection-reaction balance
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6/20/2007 Detonation 9
C2H4-3O2-9N2, 20kPa Warnatz
Characteristic thicknesses determined by energyrelease time and rate
Characteristic induction zone width
Characteristic energy release zone width
2ccdudP
6/20/2007 Detonation 10
Chemical Length and Time Scales
0.8 1 1.2 1.4
10-2
10-1
100
Normalized velocity, U/UCJ
InductionZonelength,cm
0 0.5 10
1000
2000
3000
0
0.01
0.02
0.03
0.04
0.05
OH
T
Distance, cm
Temperature,
K
OH
mole
fraction
2H2-O2-60%N2
6/20/2007 Detonation 11
Measuring Detonations
GDT
280mm diameter, 7.3m long
Velocity from time of arrival
Pressure from piezoelectric gaugesCell size from soot foils
Structure from schieren, shadowgraph, PLIF imaging
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Propagating Pressure Wave
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6/20/2007 Detonation 13
Taylor-Zeldovich Expansion Wave
closedend
L
x
particle path
t
0
openend
2
1 - at rest
3
detonation
expansion fan
Stationary region
6/20/2007 Detonation 14
Multifront waves
150 x 150 mm
Schlieren OH emission
6/20/2007 Detonation 15
Laminar and Turbulent Detonations
scale:4mm
2H2-O2-85%Ar
Po=20kPa
C3H8-5O2-60%N2
Po=20kPa
6/20/2007 Detonation 16
Turbulent detonations?2H2+O2+2CO
0.0263 atm 2.7 km/s 0.3 atm 2 .2 km/s
Generalizations of available observations suggests that turbulence
is a common property of detonation waves. This leads to the
speculation that perhaps the limits of propagation of detonation arein part by the conditions required for generating and maintaining a
turbulent zone of combustion. D. R. White Turbulent Structure of
Gaseous Detonation PF 1961
Overdriven Near CJ
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6/20/2007 Detonation 17
Cellular Structure of Detonations
H2+O2+7Ar mixture
Self-propagating near CJ velocity
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The sooted foil and cellular structure
C2H4-O2 75% Ar H2-O2 40% Ar C3H8-O2 C2H2-O2
Notice that because of its innate complexity, there is virtually no hope that
theoreticians will piece together an a prioritheory for detonation structure; they
must necessarily rely on detailed experimental observations. R. A. Strehlow
1970
Equilibrium Configurationtime average steady
B.V. Voytsekhovsky and V.V. Mitrofanov and M.Ye. Topchiyan "The
Structure of a Detonation Front in Gases 1966
6/20/2007 Detonation 19
Detonation Cell Widths
Cell width measurements
A sooted aluminum sheet
Soot foil:
1 < < 1000 mm, ~ A
6/20/2007 Detonation 20
Cell SizeMeasurements forCommon Fuels
Data from R. Knystautas,McGill university
CH4C4H10C3H8C2H6
H2C2H2
Fuel Smoke PressureFoil Oscillations
EQUIVALENCE RATIO
DETONATION
CEL
LSIZE
(cm)
0 1 2 3 4
100
50
20
10
5
2
1
0.5
0.2
C2H4
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6/20/2007 Detonation 21
Chemical structure of DetonationPLIF and Schlieren Images
6/20/2007 Detonation 22
How PLIF works
B12 : stimulated absorptiion
B21: stimulated emission
P2: predissociation
Q21: collisional quenching
A21: spontanious emission
Signal Intensity:
SF = C B12 N0 I
Quenching Q21 = f (T,background)
Absorption I = f (x)
Boltzmann fcator N0 = f (T)
Overlap integral = f (T,p,background)
A21
A21+ Q21 +P2
.
.
6/20/2007 Detonation 23
What PLIF Measures
Distance behind shock [cm]
N(OH)[mol/m
3
]
0 1 2 3 40
0.1
0.2
0.3
0.4N(OH) based on ZND calculation
calculated fluorescence based on ZND
experimental PLIF fluorescence
Compare predicted fluoresence
from ZND and PLIF models
with measured fluorescence
Experimental data obtained by
vertical averaging over
horizontal stripe
2H2+O2+85%Ar, 20kPa6/20/2007 Detonation 24
2H2-O2-12Ar,P1=20kPa
18x150mm test section
image height 60mm
Reference: J. Austin, F. PIntgen and J.E. Shepherd, Reaction
Zones in Highly Unstable Detonations, 30th Combustion
Symposium, Chicago, 2004.
image height 150mm
Narrow channel simultaneous PLIF-Schlieren
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6/20/2007 Detonation 25
Reaction zone structure
Normalized velocity (U/UCJ
)
InductionLength(cm)
0.8 0.9 1 1.1 1.2 1.3 1.4
10-2
10-1
100
2 H2 + O2 + 17 Ar
Sharp rise in OH-concentration profile marks end of induction-zone
Induction zone length is stongly dependent on shock-velocity
keystone shapes features of lower reactance
6/20/2007 Detonation 26
Reaction zone structure
Sharp rise in OH-concentration profile marks end of induction-zone
Induction zone length is stongly dependent on shock-velocity
keystone shapes features of lower reactance
2H2+O2+17Ar,20kPa (Pintgen et al 2002)
20 mm
6/20/2007 Detonation 27
0
2
4
6
8
10
1214
16
18
20
0 2 4 6 8 10MCJ
Ea/RTS
Neutral stability
boundaryC3H8-O2-N2
H2-O2-N2
H2-O2-AR
H2-N2O-N2
H2-N2O-O2-N2
H2-O2-CO2
C2H4-O2-N2
f=1
weakly unstable
(low Ea/RTS)
highly unstable
(high Ea/RTS)
stable
unstable
Lee and Stewart
JFM 1990
Classification of Detonation Front Structure
6/20/2007 Detonation 28
2H2+O2+17Ar 2H2
+O2
+ 8 N2
H2+ N2O +3 N2
C2H4-3O2-10.5N2 C3H8-5O2-9N2 C3H8-5O2-9N2
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6/20/2007 Detonation 29
Numerical Tools for Shocks andDetonation (CJ) Computations
NASA CeC code
STANJAN (in CHEMKIN)
Cantera Shock and detonation toolbox from
Caltech
GASEQ Computation not quite correct for
detonations
CHEETAH (export controlled) LLNL
6/20/2007 Detonation 30
Numerical Tools for Reaction ZoneStructure
Chemkin-based programs Reaction Design
ZND fortran program
Cantera-based programs Caltech shock and detonation toolbox
NASA,
6/20/2007 Detonation 31
Detonation Phenomena
Initiation by Blast Waves
Diffraction through tubes openingsand orifices
Limiting tube diameter
Deflagration-to-DetonationTransition
6/20/2007 Detonation 32
Initiation of Detonations
Direct initiation Requires a strong blast wave Fuel-oxygen mixtures
Exploding wire or
Electric discharge (spark) in air Fuel-air mixtures
High explosives Fuel-oxygen mixtures with DDT initiation
Deflagration-to-detonation transition Weak ignition source (glowplug or spark plug)
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6/20/2007 Detonation 33
Direct Initiation
What is the critical E needed to start a detonation?
6/20/2007 Detonation 34
Blast Wave Initiation
Subcritical, EEc
6/20/2007 Detonation 35
Plastic Bag
Containing C2H4-air
Inside View ShowingInstrumentation
Direct Initiation of Spherical Detonation
6/20/2007 Detonation 36
High-Explosive Detonating Cord Positioned on Bag Axis
Direct Initiation of Cylindrical Detonation
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6/20/2007 Detonation 37
LEGEND
0.0 1.0 2.0 3.0 4.0
EQUIVALENCE RATIO
100,000
10,000
1,000
100
10
1
0.1
0.01
INITIATIONENERGY(gramstetryl)
C2H4
H2
C2H2
C3H8
CH4
Spherical InitiationEnergy Data
Ec ~ 400UCJ2 3
6/20/2007 Detonation 38
Detonation Wave Diffraction
Detonation can fail, i.e., shock wave and
reaction zone decouple duringdiffraction
detonation
shocked reactants
shockproductsflowd
6/20/2007 Detonation 39
Detonation Diffraction Cases
Success Failure
Supercritical Critical Subcritical
Increasing cell size and reaction time
6/20/2007 Detonation 40
Tube Diameter = 1.83 m ; Bag Diameter = 3.66 m
Critical Tube Diameter Test
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6/20/2007 Detonation 41
Data from I.O Moen et al.
EQUIVALENCE RATIO
C
RITICALTUBEDIAMETERdc
(m)
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
5.0
2.0
1.0
0.5
0.2
0.1
PROPANE
ETHYLENE
HYDROGEN
ACETYLENE
NoGo
Critical TubeDiameter Data
Fuel-airdc~ 13
ordc~ 400
6/20/2007 Detonation 42
RS
Critical Radius for Reinitiation
6/20/2007 Detonation 43
Tube Initiation ConfigurationHigh-Explosive Initiation
Influence of Confinement on Propagation
6/20/2007 Detonation 44
Transmitted Air
Shock Wave
Detonation Wave
Bag Trajectory
(Contact Surface)
Still Frame from High-Speed Film
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6/20/2007 Detonation 45
Deflagration to DetonationTransition in gases
Flames and detonation propagation regimes Effect of confinement on flame propagation
Mechanisms of flame acceleration
Mechanisms involved in DDT
Pressure waves and structural response
6/20/2007 Detonation 46
Flames can become detonations!
6/20/2007 Detonation 47
Example: DDT in tubes
Obstacles or roughness is verysignificant
6/20/2007 Detonation 48
The path of DDT
DDT Process
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6/20/2007 Detonation 49
Flame passing an orifice
6/20/2007 Detonation 50
burned unburned
1. A smooth flame with laminar flow ahead
2. First wrinkling of flame and instability of upstream flow
3. Breakdown into turbulent flow and a corrugated flame
4. Production of pressure waves ahead of turbulent flame
5. Local explosion of vortical structure within the flame
6. Transition to detonation
DDT Process
6/20/2007 Detonation 51
Effect of FA on Pressure
6/20/2007 Detonation 52
Criteria For FA and DDT
Sufficient expansion ratio (>4)
Sufficiently high burning velocity Sufficient confinement
Need to reach choking regime
Sufficiently large volume L > 7large volumes Dorofeev)
d > obstructed tubes (Lee) d > 13diffraction
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6/20/2007 Detonation 53
Scaling of Detonation Onset
6/20/2007 Detonation 54
Effect of Expansion Ratio
6/20/2007 Detonation 55
References
1. A discussion of high explosive detonation from a practicingengineers perspective is given by: P. W. Cooper. ExplosivesEngineering. VCH, 1996.
2. More in-depth discussions are given in the compilation of: J. A.
Zukas and W.P. Walters, editors. Explosive Effects andApplications. High Pressure Shock Compression of CondensedMatter. Springer, 1995.
3. The classic reference on detonation is: Ya. B. Zeldovich and A. S.Kompaneets. Theory of Detonation. Academic Press, NY, 1960. Thisis an English translation of original Russian. Out of print and inmany ways out of date.
4. A more up to date theoretical treatment is given by: W. Fickettand W. C. Davis. Detonation. University of California Press,Berkeley, CA, 1979 Now available as a Dover paperback.
5. Gaseous detonations are discussed in most textbooks oncombustion.