Ignition,Combustion And Propulsion Of High-Energy-Density Fuels With Additives

There has always been a consistent ambition to improve the volumetric energy content of fuel to extend the flight distance of aerospace vehicles(like missiles and rockets)since they are always volume-limited.High-energy-density(HED)fuel,density higher than conventional refined fuel,can provide more propulsion energy and thus extend the flight range and increase the payload.However,limited by the characteristic of hydrocarbon molecules,it is hard to further improve the density of liquid fuel by chemical synthesis.Moreover,low hydrogen content in the HED fuel may induce slow ignition and low combustion completion level in scramjet engines,especially under low pressure,oxygen/fuel ratio and hypoxic environment.To solve those problems,here a relatively comprehensive and systematic study on enhancing the energy,density,stability,and combustion performances of several HED fuels(JP-10,HD-03,HD-03-I,and QC)is reported.In the aspect of improving the energy and density of HED fuels,aluminum nanoparticles(Al NPs)are selected as the most effective energetic nanoparticles by theoretical calculation,and several nanofluid fuels containing different dosages of Al NPs are synthesized.The density and volumetric energy of HED fuels increase with the increasing addition of Al NPs,and the nanofluid fuels can flow freely.A small-scale rocket combustion test shows that quadricyclane(QC)has the highest combustion efficiency,gravimetric specific impulse,and density specific impulse among the four kinds of HED fuels in the oxygen-to-fuel ratio of 1.6?2.0.Adding 15 wt%Al NPs can increase the density specific impulse of QC from 2276 N·s/m³ to 2340 N·s/m³,and the combustion flame of 15 wt%Al NPs/QC is brighter and lasts longer than that of pure QC.In the aspect of improving the stability of nanofluid fuels,Al NPs with smaller particle sizes(ca.16 nm)are synthesized by wet chemical reaction instead of purchase(ca.50 nm).Another new approach to improve the stability of nanofluid fuels is to form gelled nanofluid fuels.Here,an organic gellant(Gn)with low-molecular-mass and excellent compatibility with liquid fuels is synthesized,and four kinds of HED gelled fuels are prepared.Compared with Si O₂ gelled fuels,Gn gelled fuels show lower critical gellant concentrations(less than 1 wt%),higher thixotropy,along with better thermal and centrifugal stability.Especially,the stability performances of NPs with high concentrations(up to 30 wt%)in HED fuels are significantly improved by forming gelled fuels.Compared with Al NPs nanofluid fuels(ca.50%NPs still suspend in fuels after six weeks),almost no NPs sedimentation is found in gelled fuels after centrifugation and long storage.In the aspect of enhancing the ignition and combustion of HED fuels,energetic NPs(synthesized Al NPs),noble metal(Pt and Pd NPs),and hypergolic liquid fuel(QC)are successively used to improve the ignition and combustion of JP-10.In this dissertation,the small-scale rocket combustion test,the CO₂ laser ignition test,the shock tube test,the hot-plate ignition test,and the oxygen bomb calorimetric test are conducted to measure the parameters of specific impulse,ignition delay time,ignition temperature,and combustion efficiency,etc.Results show that 100 ppm Pd NPs/JP-10nanofluid fuel shows the lowest apparent ignition activation energy of 41.5 k J/mol,while 1 wt%QC/JP-10 blended fuel gives the highest combustion efficiency of 96.6%at the excess air ratio(?)of 2.The presence of 5 wt%Al NPs results in a reduced ignition delay time(ca.50%),a decreased ignition temperature,and facilitates the energy release of fuels during the combustion.The combustion mechanism is inferred as that the abundant active sites of Pt and Pd NPs can accelerate the breakage of C-H bonds of JP-10,while the strained and caged chemical structure of QC makes it easy to break C-H bonds so as to produce active free radicals and H atoms,and aluminum atoms preferentially react with O₂ to produce highly reactive atomic oxygen(O)and aluminum monoxide(Al O)radicals,thereby accelerating the combustion reaction.