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Aluminum (Al) nanoparticles were coated with ammonium perchlorate (AP) to obtain AP-coated Al nanoparticles with different coating amounts. The coating layers were characterized by TEM and TG. Resu...

The ignition and combustion processes of concentrated nAl/JP-10 nanofluid fuel were studied by using a CO2 laser ignition system with online diagnosis, intermediate sampling, and offline analysis. The energy release properties of aluminum (Al) nanoparticles in droplets and the influence of oxygen content on agglomerate evolution were studied. The phase separation of liquid fuel and Al nanoparticles occurs during the combustion process of concentrated nAl/JP-10 nanofluid. The burning forms of Al nanoparticles within the droplet include local, splash out, and agglomerate burning. Among them, agglomerate burning is the primary form of energy release. During the combustion process, Al particles gradually form an Al agglomerate, and the oxidation reaction of Al nanoparticles mainly occurs after the diffusion flame disappears. Oxygen content has a significant effect on the agglomerate burning of Al nanoparticles. When oxygen content is > 10%, the Al particles are successfully ignited. When oxygen content reaches 50%, a deflagration of the agglomerate occurs, and the Al particles rapidly oxidize to completely release heat and form a dense alumina sphere.

A CO2 laser ignition system was used to ignite the pure JP-10 (endo-Tetrahydrodicyclopentadiene, C10H16) and aluminum (Al)/JP-10 nanofluid droplet. Online combustion diagnosis and combustion residue analysis were combined to study the effect of solid content and atmosphere on the ignition and combustion characteristics of the Al/JP-10 nanofluid droplet. The combustion process of JP-10 can be divided into three stages, namely, ignition, steady burning, and extinguishment, while the combustion process of Al/JP-10 nanofluid can be divided into four stages, namely, ignition, mixed burning, mass burning, and extinguishment. Aluminum nanoparticles can effectively improve the volume calorific value of fuel. With the increase in solid content, the ignition time of the droplet is significantly shortened and the combustion intensity is increased. However, the increase of solid content introduces particle agglomeration problems, which decreases the oxidation degree of Al nanoparticles. Compared with air, the intensity of droplet combustion increases significantly in oxygen atmosphere. The highest combustion temperature of the fuel droplet with a solid content of 10% reached 1843 °C, the oxidation efficiency of the residues increased significantly, and the combustion efficiency of aluminum particles reached 99.26%.

The adsorption mechanism of oleic acid(OA) on the surface of aluminum(Al) nanoparticle was studied using ReaxFF molecular dynamics simulation. A surface-oxidized Al nanoparticle was constructed to simulate the single-molecule and multi-molecule adsorption processes of OA on the surface of Al nanoparticle. It was found that single OA molecule adsorbed on the surface of the Al nanoparticles through its –COOH group to form a carboxylate structure, thereby forming a chemical adsorption monolayer on the surface of Al nanoparticle. During the multi-molecule adsorption process, the chemical adsorption layer will become denser with the increase of initial density of OA in the system. When the initial density is large enough, excess OA molecules were adsorbed outside the chemical adsorption layer by physical adsorption and form a chemical-physical bilayer adsorption structure on the surface of the particles. The simulation results were verified by the adsorption layer thickness determined with XPS and the bonding structure detected with FTIR. The adsorption mechanism of OA on the surface of Al nanoparticle was found to changes from a chemical monolayer adsorption to a chemical-physical bilayer adsorption with the increase of OA concentration.

A comprehensive ignition model for single boron particles in an oxygenated environment containing O2 and H2O is developed. Microcharacteristics of the boron oxide layer on the surface of boron particles at elevated temperatures are studied. Two typical distributions of species inside the surface oxide layer are detected. One is composed of three layers [B2O3, (BO)n, and B2O3], while the other is composed of two layers [(BO)n and B2O3], both according to the order from the internal to external side of the layer. In the model development, two submodels, submodel I and submodel II, are developed with regard to two different observed species distributions in the surface oxide layer. For submodel I, it is assumed that both (BO)n and O2 are the governing species diffusing into the liquid oxide layer. For submodel II, only (BO)n is the governing species. These two submodels are combined into a new bi-directional model consisting of four key kinetic processes: evaporation of the liquid oxide layer, global surface reaction between oxygen from the environment and boron, reaction between the inner boron core and oxygen, and global reaction of boron with water vapor. The ignition time predicted by the model is in good agreement with previous experimental data.