## 2 Research Status on Anhydrous Hydrazine Fuel
### Research Status on MMH Fuel
[68] further investigated the reaction kinetics and mechanism of H-atom extraction from MMH by NO\({}_{2}\) theoretically. The dissociation and isomerization steps between the intermediate complexes were necessary for distributing the dissociated bimolecular products. At lower temperatures, the major products are cis-CH\({}_{3}\)NHNH and HONO. The branching rate of the CH\({}_{3}\)NNH\({}_{2}\) formation pathway increases with increasing temperature. On the same reaction potential energy surface, six reactions, such as the isomerization reaction of CH\({}_{3}\)NNH\({}_{2}\) catalyzed by HONO with cis/trans-CH3 NHNH, are proposed as competing reactions. Temperature- and pressure-based kinetic model rate expressions were proposed. [PERSON] et al. [69] used Fourier transform infrared spectroscopy (FTIR) to experimentally study the gas-phase chemistry of the spontaneous combustion system of MMH with oxidant NO\({}_{2}\)/N\({}_{2}\)O\({}_{4}\) at room temperature and 1 atm N\({}_{2}\) and performed quantum mechanical calculations (CCSD(T)/M06-2X) of possible reaction pathways. Based on these studies, they proposed that the oxidation of MMH in the NO\({}_{2}\) atmosphere occurs through two mechanisms: sequential extraction of H and generation of HONO; and the reaction of MMHwith asymmetric ONONO\({}_{2}\) to generate methyl nitrate. These mechanisms successfully explain all the intermediates observed experimentally. In addition to the H-atom abstraction of MMH by NO\({}_{2}\), OH reactive radicals are an essential component of the pyrolysis reaction. [PERSON] et al. [70] and [PERSON] [71] experimentally measured the total reaction rate of H-atom removal from MMH by OH, where [PERSON] et al. [71] obtained the absolute second-order OH rate coefficient expression in the temperature range of 232 to 637 K as k\({}_{2}\) = (4.59 \(\pm\) 0.83) \(\times\) 10\({}^{-11}\) exp (85 \(\pm\) 35)/ T cm\({}^{3}\) molecule\({}^{-1}\) s\({}^{-1}\). The hydroxide (OH) radical H-atom abstraction reaction showed no identifiable pressure dependence at He or N\({}_{2}\) buffer gas pressure up to 530 torrs. [PERSON] et al. [72] performed a direct kinetic study of the multichannel reaction of MMH with OH radicals and identified five hydrogen extraction channels. Electronic structure information on the potential energy surface was obtained at the B3 LYP/6-311G(d,p) level. The energies on the reaction path were refined by the BMC-CCSD method. The results show that H-atom abstraction from -NH- is the main pathway for Conformer I at low temperatures; with increasing temperature, H-atom abstraction from -NH\({}_{2}\) is a competing pathway. For Conformer II, a similar conclusion can be drawn. Starting from the Boltzmann distribution function and considering the weight factor of each conformation to calculate the total rate constant, the three Arrhenius expressions between 200 and 1000 K were fitted as k\({}_{T}\) = 1.63 \(\times\) 10 T\({}^{-244.03}\)exp(1411.5/T) cm\({}^{3}\) molecule\({}^{-1}\) s\({}^{-1}\). [PERSON] et al. [73] further obtained the detailed H-atom abstraction reaction rates of MMH + OH for the four channels by theoretical calculations in cm\({}^{3}\) molecule\({}^{-1}\) s\({}^{-1}\) and found that the rate coefficient for the extraction of central amine H to generate CH\({}_{3}\)NNH\({}_{2}\) radicals is k\({}_{1}\) = 3.37 \(\times\) 10 T\({}^{-161.295}\)exp(1126.17/T) and an extraction of terminal amine H to generate trans-CH3 NHNH radicals rate coefficient of k\({}_{2}\) = 2.34 \(\times\) 10 T\({}^{-171.907}\)exp(1052.26/T), a rate coefficient of terminal amine H extraction to generate cis-CH\({}_{3}\)NHNH radicals of k\({}_{3}\) = 7.41 \(\times\) 10 T\({}^{-202.428}\) exp(1343.20/T), and a rate coefficient of methyl H atom abstraction to generate CH\({}_{2}\)NHNH\({}_{2}\) radicals of k\({}_{4}\) = 9.13 \(\times\) 10 T\({}^{-212.964}\) exp(\(-114.09/T\)). In addition, the radical CH\({}_{3}\)NH generated by N-N bond breaking in MMH is unstable.