n-Decane-based nanofluid fuels could be one of the most promising alternative fuels as aviation kerosene for aerospace application. However, the physical and heat-transfer properties of n-decane-based nanofuels have been rarely studied, and the influence of the concentration of nanoparticles on the evaporation characteristics of n-decane-based fuels has been sparsely investigated. This paper investigated physical and heat-transfer properties and evaporation characteristics of graphite/n-decane nanofluid fuels and emphasized the concentration effect of adding graphite nanoplatelets (GNPs) on these characteristics. It was found that there are a linear increase of density and thermal conductivity, a binomial increase of viscosity, and a binomial influence on surface tension as GNP concentration increases, while the boiling point almost remains constant, and the latent heat of vaporization largely decays. There exists a critical GNP concentration of 1.75 wt % for the evaporation performance. At 0∼1.75 wt %, the increase of GNP concentration benefits the evaporation. At 1.75∼4.0 wt %, the enhancement of GNP concentration deteriorates the evaporation performance. A detailed discussion of this evaporation behavior was made, which could be attributed to multiple factors, for example, the aggregation of nanoplatelets, the changes of physical and heat-transfer properties owing to the nanoparticle concentration effect, the surfactant concentration, and the ambient temperature. The concentration of surfactants has a binomial effect, and the ambient temperature has a linear effect on the evaporation rate. This study would promote in depth understanding of physical and heat-transfer properties and evaporation characteristics of nanofluid fuels and develop the application in turbine engines and ramjet engines.

An Al/JP-10/oleic acid nanofluid fuel system has demonstrated potential in advanced combustion for aviation turbine engines. To improve the energy density of nanofluid fuel, a higher Al concentration requirement needs to be met. Correspondingly, a higher surfactant oleic acid concentration is required to maintain better dispersion stability. The increment of Al and oleic acid concentrations results in more frequent microexplosions, but a slower evaporation rate. Therefore, this paper proposes to deeply understand the contradiction of the concentration effect on the stability, physical properties, evaporation and microexplosion characteristics and obtain the best Al and oleic acid concentrations to maintain the most suitable comprehensive performance. Experiments on the stability, physical properties, evaporation and microexplosion characteristics were conducted, respectively. The analysis and discussion were then made to reveal the Al and oleic acid concentration effect on the stability, physical properties, evaporation and microexplosion characteristics. The results show that the optimum mass ratio of Al:oleic acid is 1:2 for the nanofluid fuels with Al concentrations of 2.5 wt.% or below, 1:2.5 for 5.0 wt.% or above to obtain the best stability. The physical properties of the nanofluid fuels such as density, surface tension and viscosity are linear, quartic and quadratic functions of Al concentration, respectively, relating to the internal flow and microexplosion of fuel droplets. With increasing oleic acid and Al concentration, the evaporation rates reduced, and the microexplosions became more frequent and intense. At a high ambient temperature of 600 °C, the evaporation rates were kept almost equivalent for JP-10, JP-10/oleic acid, and Al/JP-10/oleic acid fuels. It was found that the increment of ambient temperature can compensate for the reduction of the evaporation rate owing to the addition of oleic acid and Al nanoparticles, improving the evaporation and microexplosion performance.