1. 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

2. 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

3. Outline RDX – TAGzT solid propellant combustion model
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RDX – TAGzT solid propellant combustion model
RDX liquid phase decomposition analysis
GA liquid phase decomposition analysis

4. RDX-TAGzT pseudo-propellant model
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Liquid-phase chemistry is important
Important from
Initial Decomposition
point of view

5. RDX-TAGzT pseudo-propellant model
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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

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

7. Chemical Kinetics mechanism (liquid phase)
RDX-TAGzT pseudo-propellant model
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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 (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

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

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

10. RDX decomposition (liquid phase): Computation
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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

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

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

13. RDX decomposition (liquid phase): Results
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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.

14. RDX decomposition (liquid phase): Results
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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)

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

16. RDX decomposition (liquid phase): Conclusions
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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.

17. GA decomposition mechanism: Introduction
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Triaminoguanidinium Azotetrazolate (TAGzT)
Guanidinium 5-aminotetrazolate
(GA)

18. GA decomposition mechanism: Details
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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)

19. GA decomposition: Most critical pathway
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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.

20. N2 formation via Bimolecular Reaction
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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

21. GA decomposition mechanism: Model formulation
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Liquid species:
Gaseous species:
Total liquid mass:
i = NH3, HN3, N2, NH2CN, melamine

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

23. 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.

24. 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. Future Research plans Short term: Long term:
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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