Combustion of Energetic Materials Department of Mechanical Engineering Combustion of Energetic Materials Neeraj Kumbhakarna Department of Mechanical Engineering Indian Institute of Technology Bombay Note: A gist of past and current work is given in these slides. Future research plans are summarized on the last slide 1

Background and Motivation Department of Mechanical Engineering Propellant performance improvement Understand combustion phenomena thoroughly (decomposition, oxidation, phase conversion, species diffusion, etc) Investigation of combustion processes in: Cyclotrimethylenetrinitramine (RDX) High-nitrogen propellant ingredients (TAGzT, GA and GzT) 1

Outline RDX – TAGzT solid propellant combustion model Department of Mechanical Engineering RDX – TAGzT solid propellant combustion model RDX liquid phase decomposition analysis GA liquid phase decomposition analysis

RDX-TAGzT pseudo-propellant model Department of Mechanical Engineering Liquid-phase chemistry is important Important from Initial Decomposition point of view

RDX-TAGzT pseudo-propellant model Department of Mechanical Engineering Triaminoguanidinium Azotetrazolate (TAGzT) Cyclotrimethylenetrinitramine (RDX) High-nitrogen compound: produces almost no undesirable smoke or soot Has a high positive heat of formation Very little literature available on its combustion Can produce high specific impulse Extensively studied 1

RDX/TAGzT pseudo-propellant Burn rate Burn-rate sensitivity to initial temperature

Chemical Kinetics mechanism (liquid phase) RDX-TAGzT pseudo-propellant model Department of Mechanical Engineering Chemical Kinetics mechanism (liquid phase) No. Reaction Aa,c E b,c RDX 1. RDX(l) → 3 CH2O + 3 N2O 6.02  1013 36,000 2. RDX(l) → 3 HCN + 1.5 (NO2 + NO + H2O) 2.51  1016 44,100 TAGzT TAGzT(l) → 2 TAG + AzT 1.00  1016 39,200 TAG(l) → N2H4 + N2H2 + NH2NC 5.00  1015 42,000 3. AzT(l) → 2 HCN + 4 N2 35,000 a A : preexponential factor. b E : activation energy. c All units are in mol, cm, s, K, and cal. Kumbhakarna N. R., Thynell S. T., Chowdhury A., and Lin P., Combustion Theory and Modeling, Vol. 15, no. 6, 2011, pp. 933-956

Major issues: Elementary reactions vs. Global reactions RDX decomposition (liquid phase): Introduction Department of Mechanical Engineering Major issues: Elementary reactions vs. Global reactions Identity of intermediate species Probing the condensed phase

RDX decomposition (liquid phase): Experiment Department of Mechanical Engineering Fourier Transform Infrared (FTIR) Spectroscopy : Confined Rapid Thermolysis (CRT) setup – 3 types of tests

RDX decomposition (liquid phase): Computation Department of Mechanical Engineering FTIR tests: Confined rapid thermolysis of Gas phase products Condensate Residue Thermochemical analysis Gaussian 03 suite of programs Heats of formation calculated using the approach given my Osmont et al. (Combustion and Flame, 2007) Heats of reaction calculated to assess feasibility of proposed reactions

RDX decomposition (liquid phase): Results Department of Mechanical Engineering Test 1 Average FTIR spectrum showing gas phase decomposition products of 0.460 mg of RDX at 285°C. Same spectrum as in part a after subtracting H2O.

RDX decomposition (liquid phase): Results Department of Mechanical Engineering Average Mass spectrum from rapid thermolysis of RDX at 285°C and 1 atm Ar, He and residual

RDX decomposition (liquid phase): Results Department of Mechanical Engineering Test 2 Oxy-s-triazine (1680 cm-1) (1496 cm-1) FTIR spectrum of Condensate at 285°C pressed in KBr pellet along with infrared spectrum of pure RDX. (b) Same spectrum as in part a after subtracting RDX.

RDX decomposition (liquid phase): Results Department of Mechanical Engineering Test 3 (1704 cm-1) FTIR spectrum of residue left behind after heating RDX at 220°C for 10 minutes in the CRT chamber (RDX melting point - 205°C)

RDX decomposition (liquid phase): Results Department of Mechanical Engineering Formation of 1,3,4-oxadiazole from RDX (ΔHR values in kcal/mol)

RDX decomposition (liquid phase): Conclusions Department of Mechanical Engineering Major species resulting from RDX decomposition: CO, CO2, NO, N2O, NO2, c-HONO, t-HONO, HNCO, H2CO, HCOOH, HCN. m/z=70 (1,3,4-oxadiazole) and m/z=97 (oxy-s-triazine) are the two heavy molecules detected in condensed phase. Reaction mechanism for the formation of 1,3,4-oxadiazole. Kumbhakarna, N. R., Wang, S., and Thynell, S. T., Proceedings of the 44th JANNAF Combustion Subcommittee Meeting, Crystal City, Arlington, VA, April 2011.

GA decomposition mechanism: Introduction Department of Mechanical Engineering Triaminoguanidinium Azotetrazolate (TAGzT) Guanidinium 5-aminotetrazolate (GA)

GA decomposition mechanism: Details Department of Mechanical Engineering Molecular modeling (Quantum Mechanics) based calculations to develop reaction mechanism Use Gaussian 09 suite programs 55 species and 85 elementary chemical reactions Continuum based model to simulate Thermogravimetric analysis, Mass Spectrometry and Differential Scanning Calorimetry results of Neutz et al. for GA J. Neutz, O. Grosshardt, S. Schäufele, H. Schuppler, W. Schweikert,, Propellants Explosives and Pyrotechitcs, 28 (4) (2003) 181-188.

GA decomposition: Most critical pathway Department of Mechanical Engineering G+ + 5ATz- = INT5 Enthalpy (kcal/mol) INT5a1+NH3 INT5a1b Azide is next protonated INT5 Reaction Coordinate Above is shown a probable sequence for NH3 and HN3 formations, the latter involves hydrogen transfer by guanidine. The residual further reacts with guanidine to form melamine and melamine-like structures. Many other reactions examined and could play an important role in the formation of N2, NH3 and HN3.

N2 formation via Bimolecular Reaction Department of Mechanical Engineering Gu+ + 5ATz- = Gu + NH2CHNN + N2 Enthalpy (kcal/mol) TS G + NH2CHNN + N2 Reaction Coordinate Protonation of ring nitrogen is not allowed in the solution phase. Protonation of ring carbon appears attractive with immediate ring opening and release of N2. Symmetry also increases rates significantly. NH2CHNN exothermically dissociates to form N2, Guanidine is likely to react highly exothermically with NH2CH Data from CBS-QB3

GA decomposition mechanism: Model formulation Department of Mechanical Engineering Liquid species: Gaseous species: Total liquid mass: i = NH3, HN3, N2, NH2CN, melamine

GA decomposition mechanism: Results Department of Mechanical Engineering Liquid mass loss profile (Heating rate = 10 K/min). a Activation enthalpy of key reaction reduced by 2 kcal/mol.

a Activation enthalpy of key reaction reduced by 2 kcal/mol. Heat rate profiles (Heating rate = 1 K/min). a Activation enthalpy of key reaction reduced by 2 kcal/mol.

GA decomposition mechanism: Conclusions Department of Mechanical Engineering The first step observed in mass loss is caused by formation and evaporation of NH3, HN3, N2 and NH2CN whereas melamine evaporation results in the second step. Decomposition at first proceeds through endothermic reactions, but is later replaced by exothermic reactions producing the N2, NH3, and HN3. Proton transfer between Gu+ and 5ATz- is not predicted to occur by the quantum mechanics calculations for the liquid phase. Kumbhakarna N. R., and Thynell S. T., Thermochimica Acta, Vol. 582, 2014, pp. 25-34.

Future Research plans Short term: Long term: Department of Mechanical Engineering Short term: Investigate various new energetic materials with potential applications as rocket /missile propellants. Test these new materials for their performance through experiments and modeling before recommending them for production Long term: Development of Strand burner/DSC setup for thermolysis experiments Development of a computational model for combustion stability analysis to predict propellant performance under fluctuating conditions – In short develop capability to provide a comprehensive one-stop solution to propellant combustion problems