Reactive Dynamics Study of Hypergolic Bipropellants:Monomethylhydrazine and Dinitrogen Tetroxide.

To gain an atomistic-level understandingon physical and chemicalprocesses occurring at the interfaces of hypergolic propellants, wecarried out the first reactive dynamic (ReaxFF) simulations to studythe reactive hypergolic mixture of monomethylhydrazine (MMH) and dinitrogentetroxide (NTO), in comparison with the ethanol (EtOH) and NTO mixturethat is reactive but nonhypergolic. Our studies show that the MMH–NTOmixture releases energy more rapidly than the EtOH–NTO mixtureupon mixing the fuels and oxidizers. We found that the major earlychemical reactions between MMH and NTO are hydrogen abstractions andN–N bond scissions. The MMH–NTO mixture has more reactionchannels than EtOH–NTO based on statistical analyses of chemicalreaction events and channels at early stages of the dynamics. Analyzingthe evolution of product distribution over reaction time shows thatthe oxidizer (NO2) diffuses into the fuels (MMH or EtOH)for the occurrence of reactions, demonstrating the influence of physicalmixing on chemical reactions. Our simulations suggest that effectivehypergolic systems require fuels with low energy barriers of H abstractionsand/or bond scissions and oxidizers with large diffusion mobilityfor efficient physical mixing. [ABSTRACT FROM AUTHOR]