Understanding of Contradiction on Concentration Effect on Stability, Physical Properties, Evaporation and...

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.