Combustion Performance And Mechanism Of Paraffin-based Particle Composite Fuels For Hybrid Rocket Propulsion

Hybrid propulsion is a propulsion system in which different phases of fuel and oxidizer stored separately.The system combines characteristics of liquid propulsion technology and solid propulsion technology,which features high security,high reliability,low cost,pro-environment,easy thrust regulation and realization of shutting down and reboot.All of these makes the system has an extensive and broad application prospects in the propulsion field of low-cost launch and round-trip space shuttle.Currently there are two main types of hybrid propulsion solid fuel,which are paraffin-based fuel and HTPB-based fuel.Nevertheless,poor capability of paraffin-based fuel in tolerance of temperature and mechanical effect,and low fuel regression rate of HTPB-based fuel severely restrict the engineering application of hybrid propulsion.In order to solve the problem,methods of adding high caloric value nanometer metallic material and material with high thermal conductivity and high radiation absorption have been tried,but the improvement in regression rate still hardly meet the engineering requirements.Therefore realization of high regression rate becomes a pivotal issue for the engineering of hybrid propulsion technology.A new concept of structure self-disintegration put forward by Nanjing University of Science and Technology is a method of raising regression rate by modifying structure.However,the principle and theory of structure self-disintegration has not been built yet,and the combustion law of fuel has not been understood.Therefore in the experiments recorded in this paper,we take the composite fuel of paraffin and particle as the testing fuel to study combustion characteristics,combustion law and combustion theory of paraffin-based particle composite fuels(PPCF).The experiments justify the concept of structure self-disintegration and its effectiveness.In the experiments,influence law of additive particles on the combustion performance of PPCF has been obtained,the self-disintegration model of PPCF has been built,and mechanical properties of paraffin-based fuel have been modified.The research achievements have been made in the following aspects:(1)The experiment system and analyzing methods have been designed and optimized.The tough challenges of observing the radial and axial structure of combustion flame and accurately measuring regression rate of fuel have been conquered.The control accuracy of combustion chamber pressure and oxidizer flow reaches around 3%and 1%,respectively.Application range of combustion chamber pressure ranges from 0.1 MPa to 2.5 MPa.(2)Combustion performance and mechanical properties of macrocrystalline paraffin of 54#,58#,62#and 66#and microcrystalline paraffin of 58#,60#,70#and 90#have been investigated.The results show that the regression rate of paraffin fuel decreases with the increasing of its melting point,its mechanical performance increases with the increasing of its melting point.58#macrocrystalline paraffin has the best combination property.(3)Ways of mechanical modification of paraffin-based fuel as well as mechanical properties and regression rate of modified paraffin-based fuels have been investigated.The results show that mechanical properties of fuel improved by nanoscale fiber is much better by that of micron fiber,polymeric additives which make paraffin crystallization much smaller,could improve the mechanical properties of paraffin-based fuel remarkably,that the relation between the melting liquid viscosity of the formulation and regression rate meet power function relationship.The regression rate of formulation can be predicted or controlled by measuring or regulating the viscosity of the melted liquid,so that the simplified experimental process provides the basis for the preparation of paraffin-based fuel with excellent mechanical properties and combustion performance.(4)Composite fuel formulations with 5%,10%,15%and 20%combustible particles such as polyethylene,double-based propellants and magnesium have been designed.Regression rate and combustion law of PPCF under different oxidizer flow rate and 1MPa combustion chamber pressure has been obtained.The results show that the self-disintegration phenomenon of PPCF is more obvious when adding particles with high mass fraction and small grain diameter,so that its regression rate and mass burning rate are higher.Regression rate of the formulation with 10%mass fraction of polyethylene particles improved 23.0%compared with pure paraffin,regression rate of the formulation with 20%mass fraction of cylindrical double-based propellant and spherical oblate double-based propellant improved 49.8%and 61.6%,respectively,regression rate of the formulation with 15%20?m mass fraction of magnesium powder improved 59.0%.(5)Plate combustion experiments of PPCF under different oxidizer flow and combustion chamber pressure has been conducted.The results show that higher oxidizer flow rate is helpful to form stronger turbulent mixing effect,promote the structure self-disintegration effect of fuel,that higher combustion chamber pressure makes the combustion flame surface sticks closer to fuel surface and increase thermal feedback from combustion flame surface to fuel surface,which benefits the formation of self-disintegration phenomenon of PPCF.The applicative structure self-disintegration combustion model has been built based on the combustion characteristics of PPCF,and variation tendency of calculation results are almost the same with the experiment result.Analyzing chemical propulsion performance of pure paraffin and PPCF with the help of NASA-CEA program.