Study On The Preparation And Two-phase Coupling Combustion Mechanism Of AL/JP-10 Nanofluid Fuel

The calorific value of fuel is an important factor that restricts the performance of the new generation aircraft.By adding aluminum nanoparticles into the liquid fuel,aluminum-containing nanofluid fuel is obtained which can maintain fluidity of the fuel.With the high volume calorific value and excellent ignition combustion characteristics of aluminum nanoparticles,the volume energy density and ignition and combustion characteristics of the bi-phase fuel is greatly improved.In order to deepen the understanding of the preparation method and staged combustion mechanism of aluminum-containing nanofluid fuel and master the influence law of various factors on the bi-phase dispersion and ignition combustion characteristics,the preparation and energy release characteristics of the aluminum-containing nanofluid fuel are studied by both experiment and theoretical analysis.Hopefully,the results can provide some theoretical reference to the practical engineering application of this kind of fuel.First,the rheological properties and stability of the aluminum-containing nanofluid fuel were analyzed by comprehensive fluid analysis.It is found that nanoparticles tend to agglomerate and settle in the bi-phase system.The suspension stability can be effectively improved by adding non-ionic surfactant.The effects of surfactant types and preparation methods on the dispersion characteristics of this kind of fuel were studied and oleic acid was selected as the best additive.The aluminum-containing nanofluid fuel presents"shear thinning"non-Newtonian fluid characteristic.The addition of oleic acid can effectively help to form slurry suspension and reduce the overall viscosity of the system.In order to clarify the modification mechanism of oleic acid,the adsorption layer characteristics and adsorption mechanism of oleic acid on the surface of aluminum nanoparticles were studied by means of experiment methods like SEM,FTIR,surface tension test and ReaxFF molecular dynamics simulation.It is found that oleic acid can form a stable adsorption layer on the surface of aluminum nanoparticles through the chemical reaction between the carboxyl end of oleic acid and the surface of aluminum nanoparticles,so as to improve the bi-phase compatibility between aluminum nanoparticles and hydrocarbon fuel.When the concentration of oleic acid is low,oleic acid will form a single chemisorption layer with thickness of about 1.55nm.When the concentration of oleic acid is further increased,the excess oleic acid molecules will generate a physical adsorption layer outside the chemical adsorption layer,forming a chemical physical double-layer adsorption structure.The ignition combustion characteristics of Al/JP-10 bi-phase fuel droplet were studied using CO₂ laser ignition test system.It is found that aluminum nanoparticle can effectively shorten the ignition delay time of hydrocarbon fuel.The combustion process has obvious stage-distributed characteristics,which can be mainly divided into five stages:ignition stage,mixed combustion stage,stable combustion stage,agglomerate combustion stage and extinction stage.With the evaporation and combustion of hydrocarbon fuel,the aluminum particles in the droplets will agglomerate to form porous agglomerates,which will hinder the internal diffusion of oxygen,resulting in incomplete combustion of aluminum components in the agglomerates.With the increase of solid content,the combustion efficiency decreases.The ambient oxygen content has an obvious effect on the ignition combustion characteristics.The minimum ignition concentration of liquid fuel is lower than 10%while the solid aluminum particles can be ignited at oxygen concentration above 20%.Increasing the ambient oxygen concentration can effectively improve the combustion efficiency of hydrocarbon fuel and aluminum nanoparticles in the droplets.At high oxygen concentration,the combustion intensity of aluminum particles is obviously strengthened and the melting and secondary ignition of aluminum particles appear in the combustion process,which turns the combustion products into smooth alumina dense structures.After confirming the positive effect of oxygen concentration on combustion,an oxidant,ammonium perchlorate?AP?,was introduced as the surface coating material of aluminum nanoparticles to supply oxygen to the aluminum agglomerates in the process of droplet combustion,so as to improve the overall combustion efficiency of fuel.It is found that the effective coating layer of AP on the surface of aluminum nanoparticles can be formed by recrystallization method and the coating efficiency is about 60%.With the increase of AP content,the combustion efficiency of aluminum particles and hydrocarbon fuel in the droplets increased.However,due to the comparatively lower calorific value of AP itself,the overall combustion intensity of the droplets increased first and then decreased with the increase of AP amount.The AP coating layer decomposes in the combustion process.It first decomposes at low temperature during the combustion phase of hydrocarbon fuel,which promotes the complete combustion of hydrocarbon fuel.During In the early stage of combustion of aluminum agglomerates,AP decomposes for the second time at high temperature,which produces a lot of gas products to break through the agglomerate structure and provide local oxygen supply,thus promoting the oxidation of aluminum particles.Based on the mechanism of vaporization and combustion of hydrocarbon fuel and combustion of aluminum particles,an unsteady two-phase coupling ignition and combustion model of aluminum-containing nanofluid fuel was established,and the ignition delay time and combustion time of the droplets under different heating temperature,solid content and droplet diameter were calculated by MATLAB.The model was verified by comparing with the experimental results abroad,and it was found that the model can be used for the prediction the ignition and combustion characteristics of aluminum-containing nanofluid fuel.In conclusion,the preparation and energy release characteristics of the aluminum-containing nanofluid fuel are systematically studied,and the influence of the formula and various physical and chemical properties are analyzed,which lays a good theoretical foundation for the practical application of the aluminum-containing nanofluid fuel.