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Modeling High Explosive Reaction Networks
Richard P. Muller1, Joe Shepherd2, William A. Goddard, III1
1 Materials and Process Simulation Center, Caltech
and2 Graduate Aeronautical Laboratory, Caltech
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What is ASCI?
• DoE Project to Improve Simulation Science– Stockpile Stewardship
• 3 National Laboratories (LANL, LLNL, SNL)• 5 Level One University Centers (Caltech, Stanford, Utah,
Illinois, Chicago)• More Level-2 and Level-3 Centers
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Illustrations of the proposed facility
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Overview of virtual facility (VTF)
• Computational Engines– Eulerian AMR solvers – Lagrangian solver for high fidelity solid dynamics– Fluid-solid coupling
• Turbulence model development– PRISM– High resolution compressible CFD
• Materials properties computations• Materials properties data base• Facilities for high performance computing• Facilities for high performance graphics • Python scripting interface drives all simulations
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ASCI Projects at the MSC
• High Explosives:– Equations of State for Reactants and Products
– Reaction Networks
• Solids– Equations of State for Ta, Fe
• Methodology– Improved parallelization for QM
– Improved parallelization for MD
– Interface to mesoscale
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Basic research initiatives
Detonation of high explosives
Solid dynamics Compressibleturbulence
Computation of material
properties
Computational Science
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What are High Explosives?
• Most familiar one is TNT• Produce a great deal of energy, gas
• CnH2nO2nN2n n CO + n H2O + n N2
• Oxygen balanced: no reactant O2
CH3
NO2O2N
NO2
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High Explosives - Objectives• To make significant improvements in the state of the art in
simulations of the detonation of high explosives• Three tracks
– First principles• EOS of explosives, binders• Reaction networks• Reactive hydrodynamics using reduced reaction networks
– Evolutionary• Extend existing engineering models• Incorporate into high resolution computations using AMR
– Integrated simulation• Integration into framework for simulation• Model problem: corner turning problem or cylinder test
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Reaction Networks for High Explosives
HCN CN NCO N2O
HOCN HNCO NH2 N2
+OH+OH
+OH +OH
+OH
+H +N2O+NO
+NO
+H +H +NO
HCN NH NNCO N2
HNCO HNO NONH2
+O
+O
+OH
+H
+H
+H
+OH
+M
+H+N
+NO
+M
CN C2N2HCN
HCN
HCN
+OH +HCN+H
+H
+H2
+CN
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Additions to HE Reaction Kinetics
• GRI Mechanism– Right physics for small (C2NO2) species, but no HMX, RDX, TATB
• Include Melius (1990) Nitromethane Mechanism• Add in Yetter (Princeton) RDX Decomposition Pathways
– Comb. Sci. Tech., 1997, 124, pp. 25-82
• Determine analogous HMX Pathways• Compute themochemical properties for all new species• Final mechanism:
– 68 species
– 423 reactions
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RDX Decomposition Steps
N N
N
NO2
NO2O2N
N N
N
NO2O2N
N N
N
NO2O2N
H2C N
H2C N NO22
N N
N
NO2O2N
N N
N
NO2O2N
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HMX Decomposition Steps
N
N
N
N
NO2
O2N
O2N H2C N
H2C N NO23
N
N
N
N
NO2
O2N
O2NN
N
N
N
NO2
O2N
O2N
N
N
N
N
NO2
NO2
O2N
O2NN
N
N
N
NO2
O2N
O2N
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New Species Required in Mechanism
N N
N
NO2
NO2O2N
N N
N
NO2O2N
N
N
N
N
NO2
NO2
O2N
O2N
N
N
N
N
NO2
O2N
O2N
RDX
RDXR
RDXRO
HMX
HMXR
HMXRO
N
N
N
N
NO2
O2N
O2N
N N
N
NO2O2N
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Fit NASA Parameters to QM Calculations
• Obtain thermochemistry from QM– Get QM structure at B3LYP/6-31G** level
– Compute/scale frequencies
– Obtain Cp, S, H from 300 - 6300 K
• Fit to NASA standard form for thermochemical data:
T
aT
aT
aT
aT
aa
RT
H
aTa
Ta
Ta
TaTaR
S
TaTaTaTaaR
Cp
645342321
7453423
21
45
34
2321
5432
432ln
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Heat Capacity Fit
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Entropy Fit
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Enthalpy Fit
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Testing the Mechanism
• CV Calculations– T = 1500 K
– P = 1-100000 atm
• Species Profiles• Induction Times
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RDX/HMX Induction Times vs. Pressure
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RDX Combustion, P = 1000 atm
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HMX Combustion, P = 1000 atm
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Validation: Nitromethane
• Nitromethane (CH3-NO2): liquid high explosive
• Extensively studied• Compare to shock-tube data (Guirguis, 1985)
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Validation: Nitromethane
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Next HE Species
• TATB and PETN Decomposition Steps
• F-containing species important in binder
– Same fraction of F and Cl as binder– Explore reactions of intermediates
NH2
NO2
NH2
NO2
H2N
O2NO
O2N
O
NO2
O
O2N
O
O2N
F
ClF
F
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Important Unimolecular PETN Reactions
O
NO2
O
NO2O
NO2
O
NO2
O.
O
NO2O
NO2
O
NO2
+ NO2
O.
O
NO2O
NO2
O
NO2
C
O
NO2O
NO2
O
NO2
H2C O
CH2
O
O2NH2C CH2
+ NO3
C
O
NO2O
NO2
O
NO2
+ NO3
CH2
O
O2N
O
NO2
CH2
O
O2N
O.
+ NO2
CH2
O
O2N
O
NO2
CH2
OO2N
O.
H2C O
CH2
O
O2N
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Other Important Issues
• Ideal gas law poor approximation– Underestimates volume
– Overestimates density, reaction rates, factor of 15 (?)
• Put JWL EOS in CV simulation:– Tarver [J. Appl. Phys. 81, 7193 (1997)] values:
VwEeVwRBeVwRAp VRVR /)/1()/1( 2121
Value Fit #1 Fit #2
A (GPa) 1032.2 617
B (GPa) 90.57 16.93R1 6.0 4.4R2 2.6 1.2w 0.57 0.25
Eo (GPa cm3/cm3 g) 10.8 10.1