## 2 Research Status on Anhydrous Hydrazine Fuel
### Research Status on MMH Fuel
\[\mathrm{CH_{3}NHNH_{2}\rightarrow}\mathrm{CH_{3}NH+NH_{2}} \tag{7}\]  
\[\mathrm{CH_{3}NHNH_{2}+NH_{2}\rightarrow}\mathrm{CH_{3}NNH_{2}+NH_{3}} \tag{8}\]  
The rate coefficients of the MMH pyrolysis system combined with the measured total MMH decomposition rates indicate that reaction (7) is the main MMH decomposition channel. The rate coefficients (2 atm, 900-1300 K) are k\({}_{1}\) = 1.50 \(\times\) 10\({}^{58}\)\(\times\) T\({}^{-12.84}\) exp(\(-\)39,580/T) s\({}^{-1}\)k\({}_{2}\) = 3.70 \(\times\) 10\({}^{14}\) exp(\(-\)2620/T) cm\({}^{3}\) mol\({}^{-1}\) s\({}^{-1}\), respectively. The changes made to the MMH pyrolysis mechanism significantly improved the measured and simulated NH\({}_{2}\), NH\({}_{3}\), and MMH time histories over the entire range of study. [PERSON] et al. [60] studied the pyrolysis of MMH in a surge tube and measured the time histories of NH\({}_{2}\) concentrations in MMH/argon mixtures in the temperature range from 1100 to 1400 K, with pressures from 0.3 to 5 atm and showed that the above k\({}_{1}\) has a pressure dependence at 0.3 to 5 atm and the measured reaction rate constants follow a pressure-dependent trend. [PERSON] et al. [65] pointed out that simple N-N and C-N bond fission to generate radicals CH\({}_{3}\)NH + NH\({}_{2}\) or CH\({}_{3}\) + NHNH\({}_{2}\) dominates the decomposition kinetics. The pressure dependence and product branching during the dissociation of CH\({}_{3}\)NHNH\({}_{2}\) were predicted by solving the master equation. This study analyzed the kinetics of NH\({}_{2}\) + CH\({}_{3}\)NH and CH\({}_{3}\) + NHNH\({}_{2}\) unblocked binding reactions and the corresponding MMH dissociation reaction kinetics associated with rocket motor combustion over a wide range of temperatures and pressures, yielding NH\({}_{2}\) + CH\({}_{3}\)NH channels as the dominant channels. [PERSON] et al. [66] identified various MMH decomposition pathways using QCISD(T)/cc-pV\(\infty\)Z//CASPT2/aug-cc-pVTZ or QCISD(T)/cc-pV\(\infty\)Z//B3 LYP/6-311++G(d,p) quantum chemical methods. The results show that CH\({}_{2}\)NNH\({}_{2}\) has an energy barrier of 13.8 kcal mol\({}^{-1}\)- and \(\beta\)-cleavage to methyleneimine is the main pathway for the decomposition of CH\({}_{2}\)NNH\({}_{2}\) radicals. The high-pressure limiting rate coefficient of the reaction is 3.88 \(\times\) 10\({}^{19}\)T\({}^{-1.672}\)exp(\(-\)9665.13/T) s\({}^{-1}\). In addition, the pressure-dependent rate coefficient exhibits a slight temperature dependence in the temperature range from 1000 to 2500 K. They also calculated the reaction's dissociation and isomerization rate coefficients by E/J-resolution RRKM theory and porous master equation analysis at 300 to 2500 K and 0.01 to 100 atm pressures. The calculated rate coefficients associated with the latest thermochemical property data are essential in developing the kinetic mechanism of pyrolysis and oxidation of MMH and its derivatives. NO\({}_{2}\) is one of the main components of NTO, which continuously abstracts H atoms on MMH intermediate N at low temperatures to produce products (CH\({}_{3}\)NNH\({}_{2}\) and HONO), after which HONO cleaves exothermally to produce OH radicals, which is the main reaction that induces ignition. [PERSON] and [PERSON] [67] characterized the path static point of NO\({}_{2}\) extraction of H atoms from MMH by CCSD(T)/6-311++G(3 df,2p)//MPWB1K/6-31+G(d,p) and CCSD(T)/6-311+G(2 df,p)//CCSD/6-31+G(d,p) calculations. Five transition states connecting the CH\({}_{3}\)NHNH-NO\({}_{2}\) complexes, including CH\({}_{3}\)NHNH-HONO, CH\({}_{3}\)NNH\({}_{2}\)-HONO, CH\({}_{3}\)NNH\({}_{2}\)-HNO\({}_{2}\), and CH\({}_{3}\)NHNH-HNO\({}_{2}\) complexes, were determined. The highest point of the minimum energy path from the CH\({}_{3}\)NHNH\({}_{2}\) + NO\({}_{2}\) reaction asymptote to the HONO-containing product is 8.6 kcal/mol of the transition state. This value is considerably higher than the 5.9 kcal/mol estimated from the theoretical results of extracting H atoms from NH\({}_{3}\) by NO\({}_{2}\). [PERSON] et al.