Research On Combustion Characteristics Of Polyethylene-based Fuel For Solid Fuel Ramjet

Solid fuel ramjet(SFRJ)has the characteristics of simple structure,high reliability and low cost,and has broad application prospects.In this paper,the combustion characteristics of polyethylene-based solid fuel ramjet(SFRJ)were studied.(1)Study on the preparation of hydrocarbon fuel for solid fuel ramjet.The multicomponent polyethylene-based solid fuel was produced by this method,which had good compactness,no obvious shrinkage cavities and cracks,and met the experimental requirements.On this basis,the mechanical properties of the produced solid fuel were further analyzed.It was found that carbon black changed the mechanical properties of HDPE,making it brittle and easily broken;paraffin significantly reduced the tensile strength of HDPE;but carbon fiber could enhance the mechanical properties of HDPE.(2)The regression rate of polyethylene-based solid fuel was measured accurately by data reconstruction measurement method.Compared with the actual mass change after the experiment,the error was within 0.1% and the reliability was high.The accuracy met the engineering application requirements.In addition,the method could truly reflect the change of fuel inner profile structure,accurately and finely obtained the 3D distribution of the mean local regression rate,which provided an effective reference for the study of regression rate.Moreover,the method of data reconstruction was suitable for different conditions of solid fuel with innerhole axisymmetric,it had universality and general applicability.(3)In this paper,the three-dimensional distribution of the local average burning rate was studied by data reconstruction measurement method.The correlation between the mean local regression rate and total average regression rate was obtained,and the correlation between the total average regression rate and inflow air mass flux was obtained by linear fitting method.The effects of inflow conditions,engine configuration,and propellant composition on the performance of SFRJ were studied by the direct connect experiment on the ground.The results indicate that increasing swirl strength,increasing air mass flux,reducing inlet diameter of combustion chamber and reducing paraffin percentage are all helpful to improve the performance of SFRJ,while increasing the length of combustion chamber is limited to improve the performance of SFRJ.The performance of SFRJ was affected by the change of components:1)paraffin and carbon black increased the combustion rate,but paraffin had obvious effect on the regression rate;2)the addition of carbon fiber hindered the pyrolysis process of solid fuel and made it unable to Self-sustaining combustion.(4)The commercial fluid calculation software FLUENT was used to treat the fuel surface with compiling the user-defined function(UDF)of pyrolysis and mass added.And the combustion characteristics of the propellant with paraffin and carbon black under different inflow conditions were simulated.The results showed that the inflow conditions were the main factors affecting the combustion of polyethylene-based propellants.Compared with the nonswirling condition,the velocity of the shear layer and the reflow zone was higher and stronger under the swirling condition.The residence time of the propellant pyrolysis products in the reflux zone could be increased.Moreover,the pyrolysis products can be fully mixed with the incoming air to further improve the combustion efficiency.