Modeling High Explosive Reaction Networks Richard P. Muller 1, Joe Shepherd 2, William A. Goddard, III 1 1 Materials and Process Simulation Center, Caltech and 2 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 dynamicsCompressible turbulence Computation of material properties Computational Science

What are High Explosives? Most familiar one is TNT Produce a great deal of energy, gas C n H 2n O 2n N 2n  n CO + n H 2 O + n N 2 Oxygen balanced: no reactant O 2

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 HCNCNNCON2O HOCNHNCONH2N2 +OH +H+N2O +NO +H +NO HCNNHNNCON2 HNCOHNONONH2 +O +OH +H +OH +M +H +N +NO +M CNC2N2HCN +OH+HCN +H +H2 +CN

Additions to HE Reaction Kinetics GRI Mechanism –Right physics for small (C 2 NO 2 ) species, but no HMX, RDX, TATB Include Melius (1990) Nitromethane Mechanism Add in Yetter (Princeton) RDX Decomposition Pathways –Comb. Sci. Tech., 1997, 124, pp Determine analogous HMX Pathways Compute themochemical properties for all new species Final mechanism: –68 species –423 reactions

RDX Decomposition Steps

HMX Decomposition Steps

New Species Required in Mechanism RDX RDXR RDXRO HMX HMXR HMXRO

Fit NASA Parameters to QM Calculations Obtain thermochemistry from QM –Get QM structure at B3LYP/6-31G** level –Compute/scale frequencies –Obtain C p, S, H from K Fit to NASA standard form for thermochemical data:

Heat Capacity Fit

Entropy Fit

Enthalpy Fit

Testing the Mechanism CV Calculations –T = 1500 K –P = atm Species Profiles Induction Times

RDX/HMX Induction Times vs. Pressure

RDX Combustion, P = 1000 atm

HMX Combustion, P = 1000 atm

Validation: Nitromethane Nitromethane (CH 3 -NO 2 ): 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

Important Unimolecular PETN Reactions

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: