## 2 Research Status on Anhydrous Hydrazine Fuel
### Research Status on UDMH Fuel
The proposed reaction pathway and kinetic model suggest that UDMH is relatively easy to gasify under supercritical water conditions and can be fully degraded at 400 \({}^{\circ}\)C within 3 min without producing nitrate or nitrite. [PERSON] et al. [99] examined the gas-phase structures of protonated unsymmetrical 1,1-dimethylhydrazine and proton-bound dimers of UDMH and Hydrazine using infrared multiple photon dissociation action spectroscopy. Results show that the proton binds to the methylated nitrogen atom in UDMH, which has two low-lying conformers that are probably populated. The study suggests that the vibrational spectra of such complexes could be helpful in remotely monitoring rocket launches. The authors compared the measured IRMPD spectra to spectra calculated at the B3 LYP-GD3 BJ/6-311+G(d,p) level of theory to identify the structures present in the experimental studies. The study also explored the thermochemistry and structures of protonated Hydrazine and UDMH and their clusters, utilizing different theoretical methods and basis sets to formulate complete basis set limits. [PERSON] et al. [100] explored two techniques for detecting leaks of unsymmetrical dimethylhydrazine (UDMH). The first technique involves a newly developed fluorescent, colorimetric sensor with high sensitivity and selectivity but has practical limitations. The second technique uses detection tubes which are cost-effective, easy to use, and provide direct-reading results. However, the detection tube method has a limited detection range. The authors recommend future research to concentrate on miniaturizing and integrating equip ment, enhancing detection sensitivity, and creating rapid visual positioning detection methods using new detection materials and portable detectors. The factors affecting ignition are the vapor pressure, viscosity, surface tension, and density of fluids, along with reaction rates. Blending two fuels can alter their physical properties to achieve desired ignition delays and lower toxicity than hyperglogic fuels. [PERSON] et al. [101] stated that bipropellant performance parameters are measured using high-speed cameras and optoelectronic diagnostics. Specific impulse and density-specific impulse were calculated using NASA chemical equilibrium with applications utility. The study found that 2-hydroxyethyl-hydrazine (HEHN) was not hyperglogic under normal conditions with oxidizers like dinitrogen tetroxide, WFNA, and RFNA. The ignition delays of hyperglogic fuels with WFNA and RFNA were measured, and miscibility with HEHN was estimated. The global ignition delay for UH20 to UH50 blends with RFNA was shown using an optoelectronic circuit. The chemical ignition delays were similar for all blends of UDMH and HEHN and were governed by UDMH. In contrast, physical ignition delays formed a significant component of global delays. Due to launches, rocket fuel spills are unavoidable, making organizing special impact zones to separate rocket stages containing unconsumed fuel residues necessary. [PERSON] et al. [102] proposed a method for analyzing unsymmetrical dimethylhydrazine and its transformation products in soil samples using liquid chromatography-mass spectrometry, which involves separating and detecting positive ions. They validated the method using model soils and emphasized the importance of analyzing and detecting UDMH in soil samples to monitor and manage soil contamination. The authors highlighted the need for strict sanitary and hygiene standards to manage soil contamination with unsymmetrical dimethylhydrazine, which is highly hazardous and restricted to a safe impact level of 0.1 mg/kg in soils. [PERSON] et al. [103] discussed recent advances in pretreatment, analysis, and removal techniques for hazardous pollutants such as unsymmetrical dimethylhydrazine (UDMH) and related compounds. They reviewed various removal techniques and emphasized the need for further research to optimize these techniques for specific applications.