## 2 Research Status on Anhydrous Hydrazine Fuel
### Critical Assessment of the Research on Hydrazine  
While the reviewed studies on anhydrous hydrazine fuel combustion kinetics have provided valuable insights, it is essential to acknowledge the limitations and identify areas that require further investigation. The combustion studies relied on incomplete kinetic mechanisms for hydrazine fuel. These mechanisms may not accurately capture all relevant reactions and pathways involved in combustion. Further research is needed to develop comprehensive and accurate kinetic mechanisms that provide a detailed understanding of hydrazine fuel combustion behavior. \begin{table}
\begin{tabular}{c c c c c} \hline
**Reaction** & **A (s\({}^{-1}\) or cm\({}^{3}\)mol\({}^{-1}\)s\({}^{-1}\))** & **n** & **Ea (cal/mol)** & **References** \\ \hline NH\({}_{2}\) + NH\({}_{2}\) = N\({}_{2}\)H\({}_{4}\) & \(3.12\times 10^{13}\) & 0 & 0 & [55] \\ NH\({}_{2}\) + NH\({}_{2}\) = N\({}_{2}\)H\({}_{4}\) & \(5.14\times 10^{10}\) & 0 & 0 & [56] \\ N\({}_{2}\)H\({}_{4}\) (+M) = NH\({}_{2}\) + NH\({}_{2}\) (+M) & \(5.00\times 10^{14}\) & 0 & 251.21 & [38] \\ NH\({}_{2}\) + NH\({}_{2}\) = NH\({}_{3}\) + NH & \(3.37\times 10^{7}\) & 2.82 & \(2.22\times 10^{3}\) & [55] \\ NH\({}_{2}\) + NH\({}_{2}\) = NH\({}_{3}\) + NH & \(5.00\times 10^{13}\) & 0 & \(9.94\times 10^{3}\) & [39] \\ N\({}_{2}\)H\({}_{4}\) + H = N\({}_{2}\)H\({}_{3}\) + H\({}_{2}\) & \(9.60\times 10^{8}\) & 1.5 & \(4.83834\times 10^{3}\) & [39; 56] \\ N\({}_{2}\)H\({}_{4}\) + H = N\({}_{2}\)H\({}_{3}\) + H\({}_{2}\) & \(7.00\times 10^{12}\) & 0 & 10.47 & [38] \\ N\({}_{2}\)H\({}_{4}\) + NH\({}_{2}\) = N\({}_{2}\)H\({}_{3}\) + NH\({}_{3}\) & \(3.70\times 10^{6}\) & 1.94 & \(1.62934\times 10^{3}\) & [39; 56] \\ N\({}_{2}\)H\({}_{4}\) + NH\({}_{2}\) = N\({}_{2}\)H\({}_{3}\) + NH\({}_{3}\) & \(1.80\times 10^{6}\) & 1.71 & \(-5.78\) & [38] \\ \hline \end{tabular}
\end{table} 
Table 1: Some Reactions Involving Hydrazine. Figure 3: Formation of NH\({}_{3}\) from NH\({}_{2}\). (Blue line from [PERSON] et al., 2010 [55]; Red line from [PERSON] et al., 2001 [39]). Despite the significant body of research, comprehensive and well-documented experimental data still lacks. More systematic and extensive experimental investigations are needed to validate and expand existing knowledge. Additionally, more data are required at low temperatures, as current mechanisms struggle to explain spontaneous combustion at low temperatures. Studies have primarily focused on fundamental reactions and kinetics. However, further exploration and understanding of complex phenomena, such as film-cooled drying mechanisms and fuel-oxidizer mixture flame construction, are needed. These phenomena significantly impact engine performance and safety. While detailed kinetic models have been developed, there is a need for more comprehensive modeling approaches. These models should accurately capture interactions between species and reactions, considering temperature, pressure, and other environmen  
Figure 4: H-atom abstraction reaction of N\({}_{2}\)H\({}_{4}\) with H. (Magenta line from [PERSON], 2000 [56]; Cyan line from [PERSON] et al., 2001 [39]). Figure 5: H-atom abstraction reaction of N\({}_{2}\)H\({}_{4}\) with NH\({}_{2}\). (Green line from [PERSON] et al. [38], 2001; Orange line from [PERSON] et al., 2001 [39]). tal factors. Advanced and validated models will enable more accurate predictions and simulations of hydrazine fuel combustion. Theoretical calculations and modeling techniques were heavily relied upon. Experimental validation and verification of these findings are necessary. More experimental studies are required to validate proposed mechanisms and reaction rates, providing robust and reliable data for future research and application. Figure 6 further summarizes the identified limitations.