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

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

Illustrations of the proposed facility

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

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

Basic research initiatives

Detonation of high explosives

Solid dynamics Compressibleturbulence

Computation of material

properties

Computational Science

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

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

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

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

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

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

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

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

Heat Capacity Fit

Entropy Fit

Enthalpy Fit

Testing the Mechanism

• CV Calculations– T = 1500 K

– P = 1-100000 atm

• Species Profiles• Induction Times

RDX/HMX Induction Times vs. Pressure

RDX Combustion, P = 1000 atm

HMX Combustion, P = 1000 atm

Validation: Nitromethane

• Nitromethane (CH3-NO2): liquid high explosive

• Extensively studied• Compare to shock-tube data (Guirguis, 1985)

Validation: Nitromethane

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

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

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