(184q) Computational Mechanism Development for Hypergolic Propellant Systems: MMH and DMAZ

Hypergolic bipropellants (fuel and oxidizer combinations that react spontaneously upon mixing) are used for various propulsion applications such as rocket thrusters. One hypergolic system of interest is monomethyl hydrazine (MMH) and red fuming nitric acid (RFNA). RFNA is a composite oxidizer consisting of ~84% HNO₃, ~13% N₂O₄, 3% H₂O, and small amounts of inhibitors. One drawback to using MMH/RFNA is that MMH is toxic; therefore, alternative hypergols to replace MMH such as dimethylaminoethylazide (DMAZ) are desirable. In order to explore new hypergolic rocket designs and new, safer gelled hypergolic fuels and oxidizers, understanding the reaction mechanisms for these hypergols with RFNA is important.

In this study, a MMH/RFNA reaction set proposed by researchers at the Army Research Laboratories (ARL) was used to probe the reaction pathways that might dominate [1]. This set, in conjunction with new calculations/estimations, was used in our PREMIX/CHEMKIN [2,3] calculations of freely propagating, adiabatic flames to identify key mechanistic pathways occurring at a range of conditions. Post-processing of the flame predictions revealed that the MMH/HNO₃/N₂O₄ mixture was converted mainly to H₂O, NO, N₂, and CO via OH and NO₂ reactions. In contrast to combustion with O₂, no significant chain branching occurred. A reduced mechanism based on the original ARL mechanism was also developed.

For DMAZ/RFNA, no reaction set has been proposed previously. A quantitative DMAZ reaction set was developed with Gaussian 03/C.02 and Gaussian 09/A.02 [4], ideal-gas thermochemistry from a rigid-rotor/harmonic-oscillator representation, transition-state theory, and Bimolecular Quantum-RRK reaction theory [5] or RRKM. The Complete Basis Set method CBS-QB3 was employed to obtain thermochemical and kinetics parameters for key species and reactions in the set.

Acknowledgments. This work is supported by the US Department of Defense under MURI contract W911NF-08-1-0171 and the NDSEG Fellowship Program. Computational support was provided by the National Science Foundation through TeraGrid resources under grant number TG-CTS090056.

[1] W.A. Anderson, M.J. McQuaid, M.J. Nusca, A.J. Kotlar, ?A Detailed, Finite-Rate, Chemical Kinetics Mechanism for Monomethylhydrazine-Red Fuming Nitric Acid Systems?, Report No. ARL-TR-5088, Army Research Laboratory, 2009. [2] R.J. Kee, J.F. Grcar, M.D. Smooke, J.A. Miller, ?A Fortran Program for Modeling Steady Laminar One-Dimensional Premixed Flames,? Report No. SAND85-8240, Sandia National Laboratories, 1985. Modification of PREMIX 2.5, 1991. [3] R.J. Kee, F.M. Rupley, J. A. Miller, ?Chemkin-II: A Fortran Chemical Kinetics Package for the Analysis of Gas-Phase Chemical Kinetics,? Report No. SAND89-8009, Sandia National Laboratories, 1989. [4] Gaussian 09, Revision A.02, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J. Fox, Gaussian, Inc., Wallingford CT, 2009. [5] P.R. Westmoreland, J.B. Howard, J.P. Longwell, A.M. Dean, "Prediction of Rate Constants for Combustion and Pyrolysis by Bimolecular QRRK," AIChE J., 32, 1971 (1986).