Article pubs.acs.org/EF
Synthesis and Characterization of Aviation Turbine Kerosene Nanofluid Fuel Containing Boron Nanoparticles Fateme Sadat Shariatmadar and Shahram Ghanbari Pakdehi* Faculty of Chemistry and Chemical Engineering, Malek-Ashtar University of Technology, Tehran, Iran ABSTRACT: The present work studies the thermal and physical properties of aviation turbine kerosene (ATK)−boron nanofuels, including stability time, viscosity, thermal behavior, and energy content. Also, this study tries to explore the effects of the size and concentration of boron particles, surfactant type, and temperature on the stability and viscosity of nanofuel. Nanofuel samples were prepared and characterized at 0.5−4 wt % of particle loading and 0.1−2 wt % of surfactant loading ranges, for micro- and nanosized boron particles. Various surfactants, such as oleic acid, propylene glycol (PG), sorbitan oleate, Tween 85, and cetyltrimethylammonium bromide (CTAB), were used to stabilize the nanofluids. The results showed that sorbitan oleate was the best surfactant and the best weight ratio of boron particles/sorbitan oleate was about 2. With the increase of the nanoparticle concentrations from 2 to 4 wt % at 5 °C, the nanofuel viscosity was increased 24%, and with the increase of the temperature from 5 to 40 °C at a constant particle concentration (4 wt %), a 67% decrease was obtained in viscosity. Also, the effect of the particle concentration on the energy content and thermal behavior of nanofuel was determined, and it was noticed that 3 wt % boron nanoparticles could decrease the boiling point and increase the energy content of ATK fuel, significantly. aviation turbine fuel (ATF),23 the decline of diesel ignition delay time,7 and the combustion4 and evaporation5 characteristics of ethanol. They have clearly explained that the addition of the Al2O3 nanoparticle increases the thermophysical properties of the base fuels. Al2O3 nanoparticles at 1% volume concentration have shown that the viscosity of fuel increases by ∼38%.23 Wang et al.24 measured the viscosity of ethylene glycol− alumina and water−alumina nanofluids and observed that the viscosity of nanofluids was higher than that of the base fluids. Lee et al.25 measured the viscosity and thermal conductivity of water−alumina nanofluids at a low concentration of particles and remarked that the nanofluid viscosity had a nonlinear enhancement with the particle concentration. Nguyen et al.26 have shown that the viscosity of water−alumina nanofluids increases with particle loading and decreases with the temperature. Li et al.27 showed the effect of surface modification of nanoparticles on the viscosity and thermal conductivity of nanofuels. They modified the surface of Cu nanoparticles with O,O-di-n-cetyldithiophosphoric acid and prepared kerosene−Cu nanofuels. In another study, the heat transfer coefficient and thermophysical properties of ATF− alumina nanofuel were determined at various particle volume concentrations.23 The results showed a 55% increase in viscosity and only a 17% increase in thermal conductivity of ATF−Al2O3 nanofuel, for 0.3 vol % alumina at 50 °C. Another benchmark study on the nanofluid viscosity measurement showed that the viscosity of nanofluids increases with the particle concentration.28 Although many experimental data on nanofluid properties are available in the literature, the data on ATK-based nanofuels
1. INTRODUCTION Nanofluid-type fuels are a new class of nanotechnology-based fuels, which are widely used in the fields of combustion and propulsion. Nanoparticles are suspended in traditional liquid fuels and improve the energy content and performance of them.1−4 Recent studies have shown that adding energetic nanoparticles, such as boron and aluminum, to fuels can result in better performance, such as a shorter ignition delay time, higher energy content, and increased burning rate.2−10 Also, thermal properties of the base fuel can be changed because of a higher thermal conductivity of the particles.11,12 To date, many studies have explored combustion, thermophysical properties, and heat transfer performance of nanofluids. Jackson et al.13 using a shock tube found that the ignition delay time of n-dodecane could decrease by adding Al nanoparticles. Tyagi et al.7 reported that a small amount of aluminum nanoparticle (2 wt %) could improve the ignition of diesel fuel significantly. Van Devener and Anderson8 reduced the ignition temperature of Jet fuel (JP-10) by using the Cerium(IV) oxide (CeO2) catalytic nanoparticles. Van Devener and Anderson coated boron nanoparticles with ceria as a catalyst and produced air-stable particles.9,14 These unoxidized boron nanoparticles were used as fuel additives and were solvable in hydrocarbons. In another work, Young et al.15−17 used boron nanoparticles for air-breathing propulsion. A benchmark study for thermal conductivity of nanofluids was performed by Buongiomo et al.18 Their results showed the thermal conductivity of nanofluids increased with the particle concentration. Subsequently, other researchers19−21 have used different methods, including steady-state “cut bar method”, transient hot-wire method, and KD2 Pro, to find out the thermal conductivity of nanofluids. Regardless of different measurement methods, all of them observed that an increase in the temperature lead to a significant increase in thermal conductivity.22 Several researchers have studied the influence of Al2O3 nanoparticles on the thermophysical properties of © XXXX American Chemical Society
Received: June 7, 2016 Revised: August 7, 2016
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DOI: 10.1021/acs.energyfuels.6b01370 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels Table 1. Physical Properties of ATK Fuel and Surfactants chemical formula ATK oleic acid PG sorbitan oleate Tween 85 CTAB
C18H38COOH C3H8O2 C24H44O6 C60H108O8·(C2H4O)n C19H42BrN
molecular weight (g/mol)
normal boiling point (°C)
282.46 76.09 428.6
180−230 360 188.2 >260 100
viscosity (mPa s) 1.64 27.64 42 1200−2000 250−500
(20 (25 (20 (20 (20
°C) °C) °C) °C) °C)
364.45
Figure 1. SEM images of boron nanoparticles produced by the milling method. 2.5 g of boron microparticle was milled with 21.25 mL of n-hexane and 1.25 mL of oleic acid. Normal hexane was used to prevent the formation of caking and reduce the milling time, and oleic acid was used for coating of boron nanoparticles. The ball milling of boron microparticles was performed in a nitrogen atmosphere. Because oleic acid is soluble in methanol, the excess amount of oleic acid was removed by immersing the synthesized particles in methanol, and then the colloidal dispersion was centrifuged. Methanol washes the excess amount of oleic acid but not oleic acid that is bonded to the boron particle surface.14 2.3. Preparation of Nanofuel. In preparation of nanofuel, the uniform dispersion of particles in the base fuel is very important. Kerosene as a nonpolar fluid is less sensitive to charged particles, and thus, electrostatic stabilization is not effective in kerosene-based nanofuels. On the other hand, steric stabilization acts well in kerosene fuel, and the surfactant chains keep nanoparticles apart effectively.22 Kerosene-based suspensions were prepared using as-received boron microparticles and the fabricated nanoparticles. At first, surfactants were mixed with the fuel, and then particles were added. Then, the suspensions were sonicated for 30 min with a bath ultrasonic (350 W, 47 kHz, Pro-Sonic, Sultan Chemists) to disperse particles uniformly and avoid agglomeration.29 Sonication was performed in an ice bath to maintain a constant temperature (0 °C) for the mixture.29 2.4. Characterization of Boron Nanoparticles. Scanning Electron Microscopy (SEM, XL30, Philips) analysis was used to determine the size distribution and morphology of synthesized boron nanoparticles. Also, energy-dispersive X-ray spectroscopy (EDAX, EM208, Philips) was used to probe the presence of oleic acid coating on the surface of synthesized boron nanoparticles. 2.5. Characterization of ATK Nanofuel. 2.5.1. Nanofuel Stability. Detailed studies for steric stabilization in ATK−boron suspensions were performed with different types of surfactants, and the concentration of surfactants varied between 0 and 2 wt %. The particle concentration in all samples was constant (0.5 wt %). The stability of suspensions was determined by a Turbiscan Classic system (MA 2000,
are limited. ATK is an important hydrocarbon fuel for pulsed detonation engines (PDEs) and scramjets because of its high energy density and stable thermodynamic properties.1 The addition of energetic boron nanoparticles to ATK is a way to increase the energy content and performance of this fuel. Boron particles have a volumetric heat of combustion (∼136 MJ/L) higher than aluminum particles (81 MJ/L) and hydrocarbon fuels (jet fuels, ∼34−39 MJ/L).14 In the present study, the suspensions of a boron nanoparticle in ATK fuel were prepared and the effect of the surfactant type, particle size, particle loading, and temperature on the stability of ATK−boron nanofuels was investigated. Also, the viscosity, energy content, and thermal behavior of nanofuel samples were measured experimentally and compared at different boron particle concentrations.
2. EXPERIMENTAL SECTION 2.1. Materials. The boron microparticles (synthesized at MalekAshtar University of Technology, Tehran, Iran), which were used to produce boron nanoparticles, had 89 ± 1 wt % purity and a particle size range of 1−5 μm. Various surfactants, including oleic acid, propylene glycol (PG), sorbitan oleate, and Tween 85 (as non-ionic surfactants) and cetyltrimethylammonium bromide (CTAB) (as an ionic surfactant) were used (all surfactants were from Merck Co., Germany). ATK, a nonpolar solvent, was selected as the base fuel. The physical properties of different surfactants and ATK fuel are presented in Table 1. 2.2. Production of Boron Nanoparticles. Boron nanoparticles were produced by ball milling of as-received boron microparticles. The milling was carried out in a ball mill apparatus (Planetary Ball Mill, NARYA-MPM 2*250H, Amin Asia Co.) with two steel milling jars. To facilitate the particle size reduction to
