## 2 Research Status on Anhydrous Hydrazine Fuel
### Research Status on UDMH Fuel
The authors reviewed the recent advances in adsorption, catalytic wet peroxide oxidation (CWPO), photocatalytic degradation, biodegradation, and advanced oxidation processes (AOPs) for removing UDMH and related compounds from water or air. The authors recommend carefully optimizing these techniques for specific applications and developing new methods to remove UDMH and related compounds from the environment efficiently. [PERSON] et al. [104] conducted experiments to investigate the catalytic oxidation of unsymmetrical dimethylhydrazine on Pt/SiO\({}_{2}\), identifying intermediate and final reaction products and determining temperature dependencies. They found that platinum has a multifunctional role in the oxidation process. They suggested a new method for detecting unsymmetrical dimethylhydrazine in the air. The study's significance lies in its contribution to understanding the complex catalytic oxidation process on Pt/SiO\({}_{2}\). The findings have implications for detecting and removing unsymmetrical dimethylhydrazine from various environments and emphasize further research. [PERSON] et al. [105] used molecular dynamics simulations to investigate the gasification mechanism of unsymmetrical dimethylhydrazine (UDMH) in supercritical water. They found that high temperatures favor the free radical degradation reaction pathway. They proposed a mechanism for forming various products due to the oxidation of UDMH. The study confirms previous research on hydrogen production dominating at high temperatures. It identifies the transformation of the element nitrogen in UDMH to nitrogen and ammonia. The study provides valuable insights into resource utilization, highlights the potential harm of improper treatment, and proposes an alternative technology. [PERSON] et al. [106] conducted an experimental investigation on the combustion and microexplosion of gelled unsymmetrical dimethylhydrazine (UDMH) fuel droplets. It identified three distinct phases and four main phenomena in the combustion process. It includes distinctive combustion stages for freely falling droplets and droplets on a hot plate. The effects of ambient pressure and oxygen fraction on the burning rate and microexplosions were explored, and theoretical and experimental results were compared and analyzed. Understanding the combustion of single-gelled fuel droplets is crucial in predicting the spray combustion characteristics of high-energy density fuels. The study provides insights into the combustion characteristics of UDMH fuel droplets, aiding in designing high-energy density fuels for optimal performance. However, the study has limitations, such as not fully representing the behavior of larger-scale systems and the need to explore the effects of different gelling agents on combustion characteristics. [PERSON] et al. [107] discussed research on the burning behavior of gelled UDMH droplets and the effects of oxidizer stream velocity and temperature on flame structure, droplet shape and size, and the burning lifetime of gelled droplets. The study found an increased burning rate constant with pressure and that an open oxidant convective environment significantly affects the gel droplet's burning process. The burning and flame structures were sensitive to the initial velocity of the oxidizer stream. The burning process of the gel droplet was divided into four stages: heating and swelling; bubble nucleation; volume expansion; and microexplosions. [PERSON] et al. [108] discussed the occupational health risks associated with UDMH, a hydrazine derivative commonly used as a hypergolic propellant. Due to its high vapor pressure, inhalation is the most likely exposure route. Binary mixtures of UDMH and 2-hydroxyethyl hydrazine (HEH) were studied, and it was found that intermolecular attractions between the two compounds contribute to their physical properties. Using binary mixtures of UDMH/HEH offers an improved combination of favorable attributes such as reduced vapor pressure and increased boiling points.