| Hydrazine and its derivatives as traditional propellant fuels have vapor toxicity and carcinogenicity,high operating cost and potential safety hazards.Hypergolic ionic liquids(HILs)have the advantages of low vapor pressure,low toxicity,wide liquid temperature range and high thermal stability.They are believed to be the most promising new generation of propellant fuels to replace hydrazine and its derivatives.In this thesis,23 kinds of ionic compound are synthesized,17 of them belong to HILs.Their properties are calculated and tested,including viscosity,density,melting point,decomposition temperature,heat of formation,specific impulse and ignition delay time.The results show that these HILs possess the density of 0.908-1.270g·m L-1,the viscosity of 15.2-763 c P,the decomposition temperature of more than200°C,and the shortest ignition delay time of 8 ms.The influences of cation and anion structures on the properties of HILs are studied for the first time.The longer the side chain of cations,the higher the viscosity,the lower the density and the lower the heat of formation.The higher the unsaturation of cation side chain,the higher the heat of formation but the lower the thermal stability.These studies found that the low viscosity has a strong correlation with the short ignition delay time.The hypergolicity of HILs is explored,the frontier orbital energy gaps between anion and nitric acid are calculated.It is found that hypergolic anions possess smaller energy gaps than non-hypergolic anions.The concept of hypergolic reactive groups is proposed,and the number and type of these groups largely determine the degree of ignition delay time.The free energy and enthalpy changes of initial reactions between three anions and oxidants are calculated.The steps of evaluating and predicting hypergolicity are summarized.It is difficult for a single ionic liquid to meet all the requirements of practical application.Two strategies to modify HILs are proposed to solve this problem.The addition of 0.02 wt%graphene can reduce the viscosity of 1-cyanopropyl-3-methyl-imidazolium dicyanamide by 13.8%at 15°C and shorten the ignition delay time by49%.The viscosity of ionic liquids can be greatly reduced by a small amount of ethanol.The viscosity of 1-cyanopropyl-3-methyl-imidazolium dicyanamide can be reduced by 16.4%at 25°C after adding 5 mol%ethanol and its ignition delay time also can be reduced by 41%.The molecular dynamics simulations indicate that the interactions of anion and cation are influenced by ethanol and ionic diffusivity is improved.The strategy of designing hypergolic multi-ionic liquids is put forward to combine the advantages of different ions and get stable liquid fuel with improved performances.Three different systems are studied and show different features:imidazolium-dicyanamide-cyanoborohydride shows the shortest ignition delay time of3 ms at a proper ratio.Imidazolium-oxygen acid-dicyanamide gets improved in terms of density,oxygen balance and specific impulse,it can be applied as a monopropellant fuel.Imidazolium-guanidinium-dicyanamide possesses higher density and specific impulse,and ignition delay time can keep original level.The radial distribution functions and self-diffusion coefficients are calculated through molecular dynamics simulations.And it is found that the interaction system between three ions are totally different original single ionic liquid.The diffusivity of ions changes with ionic ratio,and self-diffusion coefficients show similar variation trend with viscosity.This thesis makes a comprehensive study on HILs,and develops a variety of new ideas and strategies from structure design to performance modification,which provide theoretical basis and scientific data for their practical application as alternative propellant fuel. |
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