Understanding of Contradiction on Concentration Effect on Stability, Physical Properties, Evaporation and Microexplosion Characteristics of Al/JP-10/Oleic Acid Nanofluid Fuel

Abstract

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.

Secondary Atomization and Micro-Explosion Effect Induced by Surfactant and Nanoparticles on Enhancing the Combustion Performance of Al/JP-10/OA Nanofluid Fuel

“…When the concentration of Al nanoparticles is beyond 1.5 wt.%, the combustion rate of the droplet decreases with an increasing Al nanoparticle concentration. This is possibly due to the agglomeration and aggregation of Al nanoparticles inside the droplets without the aid of a surfactant [21]. This trend is consistent with the influence of the nanoparticle concentration on the combustion rate of nano-graphene/refined kerosene nanofluid fuel without surfactant reported by Yadav et al [28].…”

“…For the Al/JP-10/OA nanofluid fuel system, one conflict is that there are different Al concentrations for obtaining the best suspension stability, physical properties, evaporation, and micro-explosion characteristics, as demonstrated in our previous work [21]. Similarly, the concentrations of OA surfactant and Al nanoparticles possibly play an important role in influencing the combustion performance.…”

“…The materials used in this work and the preparation method for the nanofluid fuel are consistent with those in our previous work [21]. Al nanoparticles with a median size of 50 nm were selected as the additive, OA was used as the surfactant, and JP-10 was used as the base fuel.…”

“…Simultaneously, it is noted that our previous work [21] deeply revealed the contradiction of the concentration effect on the stability, physical properties, evaporation, and microexplosion characteristics and obtained the best Al and OA concentrations to maintain the most suitable comprehensive performance. Therefore, the best formula for a Al/JP-10/OA nanofluid fuel system to improve the combustion performance must comprehensively consider and balance multiple aspects in practical engineering applications.…”

“…Correspondingly, to enhance the dispersion stability of Al nanoparticles in JP-10, a surfactant is required. The surfactant with the best effect on the stability enhancement of the Al/JP-10 system is OA [21]. Therefore, in this work, the Al/JP-10/OA nanofluid fuel system was selected to conduct experiments and further evaluate its combustion characteristics.…”