Effect of Droplet Size on the Burning Characteristics of Liquid Fuels with Suspensions of Energetic Nanoparticles

Transcription

1 8 th U. S. National Combustion Meeting Organized by the Western States Section of the Combustion Institute and hosted by the University of Utah May 19-22, 2013 Effect of Droplet Size on the Burning Characteristics of Liquid Fuels with Suspensions of Energetic Nanoparticles Saad Tanvir 1 and Li Qiao 1 1 School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN, Introduction The objective of this paper is to understand the effect of droplet size (decreasing from a millimeter scale to a micron scale) on the combustion characteristics of nanofluid fuels (liquid fuels with suspensions of energetic nanoparticles). An experiment was developed to produce a droplet stream with droplet sizes ranging from µm and spacing between µm. The droplet stream was ignited using a heated coil, producing a stable droplet stream flame. Pure ethanol and ethanol with the addition of aluminum nanoparticles at varying concentrations were tested. Macroscopic visualization of the flames showed micro-explosions to appear in the flame as the nano aluminum burns and escape the flame front. Ethanol burned with a blue flame indicating little or no soot formation inside the flame. Residue analysis on the stream showed that the aggregation intensity increases with increasing particle concentration. The aggregate structures are dominated by chain like structures and spherical clusters. The burning rate increased with increasing particle concentration. For low concentrations nanofluids (up to 2wt.% aluminum), the burning rates remained stable, following the D 2 -Law of droplet burning. For higher concentrations, the burning rate reduces as a function of time hence deviating from the D 2 -Law. Increasing particle concentration increased the maximum temperature of stream flame. The nanofluid droplet stream burned at a higher temperature downstream as compared to upstream due to the burning of nanoparticles which burned at a higher temperature then that of ethanol. Metallic materials, such as aluminum, with their high combustion energies have been used as additives in propellants and explosives [1]. With recent advances in nanoscience and nanotechnology, the production, control and characterization of nanoscale energetic materials is possible. Due to their high surface areas, these nanoparticles offer shortened ignition delays, reduced burning times and more complete combustion than micron sized particles [1, 2]. Recently, the combustion and propulsion communities have shown an increased interest in developing high performance nanofluid-type fuels. The idea is to suspend nanomaterials (fuel additives such as energetic nanoparticles or nanocatalysts) in traditional liquid fuels to enhance performance. The unique features of the additives, could improve power output of propulsion systems and possibly reduce ignition delay [3, 4]. 1

2 Little work has been done on studying the ignition and burning behavior of nanofluid-type fuels. Tyagi et al. [5] explored the ignition properties of aluminum/diesel and aluminum oxide/diesel nanofluid fuels using a simple hot plate experiment. Results showed enhancement in ignition probability for nanofluid fuels as compared to pure diesel fuels alone. Beloni et al. [6] studied the effect of adding metallic additives ( pure aluminum, alloyed Al 0.7 Li 0.3, and nanocomposites 2B+Ti) to decane on flame length, flame speed, emissions and temperature over a lifted laminar flame burner. Similar studies by Jackson et al. [7] and Allen et al. [8] found that the addition of a small amount of aluminum nanoparticles to n-dodecane and ethanol in a shock tube significantly reduces ignition delay of both nanofluid type fuels. Young et al. [9, 10] explored the potential of using nano-sized boron particles as fuel additives for high-speed airbreathing propulsion. It was observed that boron particle can be successfully ignited in an ethylene/oxygen pilot flame. However, sustained combustion of boron particles can be achieved only over a critical temperature of around 1770 K. Van Devener et al. [3, 4] conducted one of the first works in studying the catalytic combustion of JP-10 using CeO 2 nanoparticles and later boron nanoparticles coated with a CeO 2 catalytic layer. Results showed a significant reduction in the ignition temperature of JP-10. The boron core of the particles also increased the energy density of the JP-10 fuel. Rotavera et al. [11] found that the addition of CeO 2 nanoparticles in toluene significantly reduced the soot deposition on the shock tube walls under high fuel concentration conditions. The combustion behavior of nanofluid-type fuels depend on multiple factors such as type, size and concentration of the nanoparticles added, the nanofluid fuel s colloidal stability as well as the base liquid fuels used. Furthermore, the unique physical properties of nanofluids such as enhanced thermal conductivity and optical properties [12-17] may also affect their burning behavior. Motivated by the aforementioned work, Gan et al. [18, 19] explored the burning characteristics of single fuel droplets (in the range of mm in diameter) containing nano and micro sized aluminum particles. The results show different burning behavior for micro suspension and nano suspensions. For the same particle concentrations, the microexplosive behavior was more aggressive in the microsuspension as compared to the nanosuspension. This was attributed to the difference in the structure of the agglomerates formed during the evaporation and combustion process. It was observed that for nanosuspension the aggregate formed was dense and porous via Brownian motion. On the other hand, the microsuspension resulted in an aggregate that was rigid and impermeable via fluid transport (droplet surface regression and internal circulation). It was also noted that ethanol based nanofluids were more stable than decane solutions. Gan et al. [18, 19] later expanded this work by studying the combustion behavior of boron and iron (due to their higher energy densities than aluminum) based nanofluids with both ethanol and n-decane as the base fluids. One of the observations made was that for a high boron particle concentration, nanofluid droplets burned inconsistently. Some boron particles burned simultaneously with the liquid fuel, where as the rest formed an aggregate on the fiber that burned after all the liquid fuel had completely burnt out for the n-decane case but not for the ethanol case (because the high flame temperature melted the agglomerate). A similar trend was observed for the iron nanoparticles. However, larger aggregates in the iron nanofluids exploded shortly after ignition resulting in the formation of jets in multiple directions. For dilute ethanol based suspensions, simultaneous combustion of ethanol and nanoparticles was seen; similar to that observed earlier [18, 19]. 2

3 These results show that particle aggregation plays an important role in the combustion behavior of nanofluid droplets. Note in these work, the diameter of the droplets is in the range of mm. For smaller droplets such as in a spray, however, particle aggregation may be a lessserious issue. The degree of aggregation and how it affects the overall combustion behvaior depend on a comparison of the time scales: the characteristic droplet evaporation (or combustion) time vs. the characteristic particle aggregation time. For a large droplet, the characteristic time of particle aggregation may be on the same order as to that of droplet evaporation and burning. As a result, large aggregation structures will form during the process of evaporation and burning. Eventually, a large agglomerate can be formed that will burn during a later stage. However, for much smaller droplets that are not significantly larger than the nanoparticles or an agglomerate (similar to a 10- m droplet vs. 100-nm nanomaterial), the aggregation timescale may be much longer than the characteristic droplet-burning timescale, which means that until the droplet is completely evaporated and burned, the particles inside may have insufficient time to form a solid aggregate. This would essentially change the distinctive combustion stages and the overall burning characteristics. Motivated by these, we developed a droplet stream combustion experiment which can produce a stream of droplets of micron sizes ( µm). The goal of this paper is to quantify the effect of droplet size on the combustion behavior of nanofluid fuels. 2. Experimental Methods 2.1 Fuel preparation and characterization The nanofluid fuels are prepared using physical and chemical (where required) dispersion methodologies as discussed in the earlier study [18, 19]. The appropriate amounts of particles were vigorously stirred with the base fuel. This was followed by sonication of the colloidal mixture in an ultrasonic disrupter (Sharpertek, SYJ-450D) to avoid and delay particle agglomeration. The sonication was performed in an ice bath to maintain a constant temperature of the nanofluid. The nanofluid was sonicated of 8 minutes. The sonicator generates a series of 4 second long pulses with 4 second spacing. Ethanol was used as a base fuel for the current study. Aluminum nanoparticles (averaged size of 80 nm, from Nano-structured & Amorphous Materials, Inc.) were considered as additives to ethanol. Figure 1 shows the SEM (Scanning Electron Microscopy) image of the nanoparticles. The amount of particles added is precisely measured using an analytical scale (Torban AGZN 100) with an accuracy of 0.1 mg. Nanofluid samples prepared (0.1-5 wt.% aluminum in ethanol) maintained excellent suspension quality for over 2 hours without the presence of a surfactant. This is because ethanol is a polar and hydrophilic liquid. Hence a good suspension of nanoparticles with hydrophilic oxide surface in ethanol is maintained. 3

4 Figure 1: SEM image of 80nm Aluminum particles 2.2 Experimental Setup Droplet Stream generation and ignition Figure 2 shows the schematic of the droplet stream generation system. The setup consists of a vibrating orifice droplet generator, a mechanical syringe pump system, a wave function generator, a linear amplifier, and a high speed camera along with a backlight. The droplet generator (Drop Generator LHG-01), containing a piezoceramic disk and 100 µm orifice, is oriented so that the stream is in a downward direction. A KdScientific syringe pump system supplies the nanofluid into the droplet generator at the specified constant volumetric flow-rate via Festo PL-6 tubing. The wave function generator (Model 519 AM/FM Function Generator) is connected to the linear amplifier (Piezo Systems, Inc. Model EPA-104) whose signal is sent to both the piezoceramic disk inside the droplet generator as well as to the digital oscilloscope (Tektronix, TDS 2024B) to monitor the actual output of the amplifier. 4

5 Figure 2. Schematic of the droplet stream generation system As the fluid is forced through the droplet generator, the square wave signal causes the piezoceramic disk within the droplet generator to oscillate and apply longitudinal disturbances to the fluid jet, thus perturbing the fluid. In accordance with the Rayleigh Instability theory, the fluid, when disturbed at the proper frequency, will break-up from a uniform jet stream into a uniform stream of equally sized and spaced spherical droplets. Quantitative analysis was conducted on the stream to monitor droplet size and spacing as a function of applied frequency and volumetric flow rate using a high speed camera (a monochrome Phantom V7.3 camera with a speed of 6688 fps at a resolution of and a color Photron Fastcam camera with a speed of 1000 fps at a resolution of ). A frequency of 20 khz was used for the preliminary combustion experiments. This gives the maximum distance (550 µm) between each droplet of diameter ~ µm. The volumetric flow rate had little impact on the droplet sizes and spacing for low applied frequencies. The orifice assembly and droplet generator were thoroughly cleaned after each test to ensure that no nanoparticle deposits are left on the walls of the tube and in the orifice plate. A heated nickel coil, attached to a high voltage power supply, was used to ignite the droplet streams. The coil was placed at a distance of 0.8 inches downstream of the orifice. A DSLR camera was used to capture the burning behavior of the stream. A protective screen was placed around the flame to get better imaging and to isolate the flame from external air disturbances. 3. Results and Discussion 3.1 Physical appearance of the flames and combustion residue analysis Flame tests were conducted for pure ethanol and ethanol with 0.1, 0.5, 1.0, 2.0 and 3.0 wt.% aluminum nanoparticles. Figure 3 (a-e) shows the comparison of the droplet stream flames of the fuels. The initial droplet size was 176 µm and an average spacing between the droplets was set at 550 µm for all tests conducted. Figure 3 (a) shows a blue droplet stream flame for pure ethanol. The blue stream flame is indication of little or no soot formation inside the flame. Once 5

6 0.1 wt% aluminum nanoparticles were added to ethanol, we saw micro-explosions to appear in the droplet flame because the aluminum particles burned. These explosions become more prominent as particle concentration increases. Figure 4 shows a closer look at this phenomenon. The burning and escaping of particles from the flame is similar to what was observed in previous work [18, 19]. As discussed earlier, due to the larger size of droplets used by Gan et al. [18, 19], the nanoparticles had the tendency of forming a large agglomerate and the agglomerate burned at a later stage after the liquid fuel had been completely combusted. This, however, was not observed in present flames. Figure 3. (a) Pure Ethanol (b) 0.1wt.% Aluminum in Ethanol (c) 1.0 wt.% Aluminum in Ethanol (d, e) 2.0 wt.% Aluminum in Ethanol 6

7 Figure 4. Nano aluminum combustion inside a 1.0wt.% Al in ethanol nanofluid flame Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX) analysis was conducted on samples collected from within the burning droplet stream as well as the escaping combusted nanoparticles that appear downstream of the flame (as shown in Figures 3 and 4). All samples were allowed to dry and their residue was scanned using SEM. Figure 5 (a), (b) and (c) show SEM images for samples collected from within the stream for 1.0, 2.0 and 3.0 wt.% Al in ethanol respectively. 7

8 (a) (b) Figure 5. SEM images of samples from within the stream flame; (a) 1 wt.% Al in Ethanol; (b) 2 wt.% Al in Ethanol; (c) 3 wt. % Al in Ethanol Aggregation type and sizes of the three samples Density increases: We noticed that both aggregation density and aggregate sizes increase upon further addition of nanoparticles to ethanol. For the 1 wt.% aluminum case (Figure 5a), we saw that aggregate sizes vary from a few nanometers to about 30 micrometers. Majority of the aggregates took the form of an elongated chain like structure. The reason of formation of such a structure is still unclear. There were however some spherical clusters of variable sizes present. A similar trend was observed for the 2 wt.% aluminum case (Figure 5b). The aggregate sizes were in fact bigger with some chain like agglomerates exceeding 50 µm. The presence of spherical clusters became more prominent as compared to 1 wt% aluminum case. Furthermore, the density of the aggregates present within the sample increase illustrating a larger presence of Al or Al 2 O 3 within the sample. A much different structure was observed however for the 3 wt.% aluminum case (Figure 5c). The structure comprises of large chain like lumps of aggregates. The density and size of the aggregates significantly increases from the 2wt.% case. 8 (c)

9 EDX analysis on the three samples shows a higher Al/O ratio for samples of higher aluminum concentration. The results show that the Al/O ratio increases from 0.66 for 1 wt.% aluminum case to as high as 1.58 for 3 wt.% aluminum. A higher Al/O can be attributed to an increased amount of unburned aluminum aggregates due to incomplete nanofluid combustion as the aluminum concentration in the sample increases. Figures 6 (a), (b) and (c) show SEM images of deposits of escaped burning aluminum particles (highlighted in Figure 6) for 1.0, 2.0 and 3.0 wt.% Al in ethanol streams respectively. While observing these images we find a similar trend to the samples collected directly from the stream flame. The aggregate density and sizes are much smaller for the 1 and 2wt.% aluminum cases (less than 10µm) than that of 3wt.% aluminum case where the size of some aggregates exceed 50µm. Another observation is that the shape of aggregates is much different in the 3wt.% case in comparison to the others. For the 1 and 2 wt.% aluminum case the aggregates are mostly in spherical clusters. Whereas for the 3 wt.% aluminum case the aggregates are dominated by chain like structure with spherical clusters attached to their ends. Furthermore the amount of aggregates per unit area increases upon addition of nanoparticles. This increase is more significant once we increase the aluminum concentration in the sample from 2 wt.% to 3 wt.%. EDX analysis on the three samples shows a higher Al/O ratio for samples of higher aluminum concentration. The results show that the Al/O ratio increases from 0.64 for 1 wt.% aluminum case to as high as 1.27 for 3 wt.% aluminum. A higher Al/O can be attributed to an increased amount of unburned aluminum in the combusting aluminum nanoparticle aggregates leaving the stream flame as the aluminum concentration in the sample increases. EDX analysis was also carried out for singled out aggregate structures for all the cases above. The value of Al/O ratio remained between 1.75 and The higher values attributed to denser spherical clusters and the lower to the less dense chain like aggregate structures. 9

10 (a) (b) Figure 6. SEM images of samples from deposits of escaped burning particles; (a) 1 wt.% Al in Ethanol; (b) 2 wt.% Al in Ethanol; (c) 3 wt. % Al in Ethanol 3.2 Effect of particle addition on burning rate Backlight shadowgraphy using the high speed (Phantom V7.3, Vision Research) camera was used to determine the burning rate - variation of droplet diameter as a function of time. Figure 7 shows the variation of the droplet diameter squared as a function of time for nanofluids with aluminum concentration varying from 0.1 to 4 wt.%. Starting with 0.5 inches downstream of the end of the coil, the measurements were taken in increments of 0.5 inches downstream of the flame source. The speed of the falling droplets within the stream was calculated using the high speed camera and was estimated to be 6.37 m/s. (c) 10

11 Figure 7. Variation of droplet diameter as a function of time for the ethanol-based nanofluid fuels with varying aluminum concentrations. From Figure 7 we observe that for pure ethanol and for nanofluids with low concentrations of aluminum ( wt.%) the squared of the droplet size decreases linearly with time. If linearly fit, the data points for pure ethanol and nanofluids with low aluminum concentrations ( wt.%) give an R 2 (Coefficient of Determination) value of equal to or over 0.99; indicating an excellent fit. Hence, for these cases we can conclude that the droplet size regresses following the classical D 2 -Law for droplet combustion. The 2 wt.% case gives an R 2 value of indicating good correlation with the D 2 -Law. For higher concentrations however, this is not the case. For 3 and 4 wt. % aluminum nanofluids, the droplet size regression deviates from the D 2 -Law forming bent curves. The deviation becomes more significant as the particle concentration increases. This behavior could be attributed to multiple factors. The change in physical properties such as thermal conductivity, viscosity, surface tension, may affect heat of vaporization. Moreover, the deviation from the D 2 -Law could be the effect of particle aggregation behavior. Particle aggregation affects fluid dynamics inside a combusting droplet and therefore potentially impacts the combustion process. However further investigation is required to fully understand this phenomenon. Figure 8 shows the variation initial burning rate (measured at a location of 0.5 downstream of the heating coil) and the burning rate further downstream (measured at a location of 3.5 downstream of the heating coil) as a function of aluminum concentration inside the 11

12 nanofluid. We observed that the initial burning rate increases with increasing particle concentration. Since aluminum nanoparticles have a higher thermal conductivity and radiation energy absorption ability, this leads to an increase in thermal conductivity and radiation absorption of the resulting Al/ethanol nanofluid ensuing faster evaporation and hence an elevated burning rate. As we move downstream of the initial measuring point, we notice that the rate of burning rate increases reduces. The trend is also evident from Figure 9. Figure 8. Variation of initial burning rate with the addition of aluminum nanoparticles For low concentrations nanofluids (up to 1wt.% aluminum), the burning rates remain stable, following the D 2 -Law of droplet burning. For higher concentration cases, the burning rate varies throughout the entire evaporation process in situations in which the D 2 -law does not apply. As we explore the burning rate variation as a function of time as we notice that the burning rate for higher particle concentration nanofluids follows a decreasing trend. This is illustrated in Figure 9. The decreasing trend is more evident in the 3 and 4 wt.% aluminum cases. This reduction in burning rate downstream of the flame can be attributed to the aggregation of nanoparticles inside the nanofluid during the combustion process. In section 3.1 (Figure 5c), we witnessed a significant increase in aggregation density in the samples collected from within the flame. The evident increase in aggregation at higher particle concentrations (3 and 4 wt.% aluminum) inhibits diffusion of the base fluid to the surface of the droplet. Even though the increase in particle concentration would increase the radiation absorption of the nanofluid; in this case however, this effect is overcome by the hindrance to fluid diffusion inside the droplet caused by particle aggregation. Hence the rate of droplet regression decreases, reducing the overall burning rate of the droplet. 12

13 Figure 9. Variation of Burning Rates as a function of time 3.3 Infrared imaging and temperature distribution of the droplet stream flames The temperature distribution of the droplet stream flames is determined using a high-speed megapixel infrared (IR) camera (SC6100 HD Series from FLIR Systems, Inc.). An integration time of ms and a frame rate of 30 Hz were used for recording infrared images from the flame. The camera was placed 0.125m from the stream flame. From the collected infrared images, we were especially interested the effect of the addition of nanoparticles on flame temperature. Figures 10 and 11 show the temperature distribution inside the droplet stream flame with and without the presence of nanoparticles upstream (measured at 3 inches downstream of the heating coil) as well as downstream (measured at 6 inches downstream of the heating coil) when the particles started to burn. For these experiments, the droplet diameter is 176 µm and the thickness of the droplet stream flames was estimated to be 9-11 mm. Note that the temperatures are not the actual flame temperatures and will be calibrated in the future. We find that the maximum temperature of the stream flame increases as the particle concentration increases. This is consistent with the trend of the measured burning rate, that is, the burning rate increases as the particle concentration increases. Furthermore, the temperature distribution within the stream flame is consistent with previous work on droplet stream flames [20]. We observe a local minimum temperature is at the axis of the droplet. The maximum temperature is reached on either side of the stream axis where the flame sheet is believed to be present suggesting a nearly cylindrical flame sheet around the droplet stream. Beyond this point the temperature reduces to ambient temperature. 13

14 2.5 inches Figure 10. Upstream thermal images of the droplet stream: (a) Pure Ethanol; (b) 1wt.% Al in Ethanol; (c) 2wt.% Al in Ethanol; (d) 3 wt.% Al in Ethanol As the nanofluid droplet stream moves downstream (Figure 11), we observed that the flame temperature increases as compared to the upstream temperatures. For the nanofluid cases, the red spots indicate burning of aluminum particles at a higher temperature. Furthermore, disruption was observed inside the flames suggesting an unsteady behavior of the droplet stream flame. There are two reasons for this: first, due to the continuously reducing droplet size, the stream becomes weak and the slightest ambient disturbance causes disruption in the flame. Second, the particles and/or particle aggregates present inside the droplets escape the surface of the droplets and start to burn causing micro-explosions within the stream. This could largely distort the stream flame. Macroscopically visualizing the stream for nanofluids, we did witness nano aluminum burning and particles escaping the flame (Figure 4). Another observation we see from Figure 11 is that the hottest part of the flame is the burning of aluminum and aluminum aggregates, reaffirming that aluminum burns at a higher temperature than ethanol hence increasing the temperature of the flame. Thin filament pyrometer technique will be used to determine the absolute flame temperature from the temperature of the inserted filament of known emissivity while accounting for the radiative heat loss using the correlation used by Blunck et al. [21]. Beside the heat release from burning particles, which tend to increase the droplet stream temperature, there is a possibility of an increased droplet temperature resulting from radiation absorption by nanoparticles. These effects will be quantified in the near future. 14

15 2.5 inches Figure 11. Downstream thermal images of the droplet stream: (a) Pure Ethanol; (b) 1wt.% Al in Ethanol; (c) 2wt.% Al in Ethanol; (d) 3 wt.% Al in Ethanol 4. Conclusions A droplet stream combustion experiment was developed to understand the effect of droplet size on the overall burning behavior of nanofluid fuels liquid fuels with stable suspensions of energetic nanoparticles. Ethanol with or without suspension of aluminum nanoparticles at varying concentrations were considered. Major conclusions from this work are: (1) A Macroscopic visualization of the flames showed micro-explosions to appear in the flame as the nano aluminum burns and escape the flame front. The blue stream flame of ethanol was an indication of little or no soot formation inside the flame. (2) Residue analysis on the stream showed that the aggregation intensity increases with increasing particle concentration. The aggregate structures are dominated by two types of aggregate forms: chain like structures and spherical clusters. More investigation is required on why such structures are formed. (3) The burning rate increased with increasing particle concentration. For low concentrations nanofluids (up to 2wt.% aluminum), the burning rates remained stable, following the D 2 - Law of droplet burning. For higher concentrations, the burning rate reduces as a function of time hence deviating from the D 2 -Law. (4) The maximum temperature of the stream increased with increasing particle concentration. The maximum temperature is reached on either side of the stream axis where the flame sheet is believed to be present suggesting a nearly cylindrical flame sheet around the droplet stream. The nanofluid droplet stream burned at a higher temperature downstream 15

16 as compared to upstream due to the burning of nanoparticles which burned at a higher temperature then that of ethanol. Thin filament pyrometer technique will be used to determine the absolute flame temperature and will help us quantify these effects. Acknowledgements This work has been supported by the National Science Foundation (NSF). References [1] R.A. Yetter, G.A. Risha, S.F. Son, Metal particle combustion and nanotechnology, P Combust Inst, 32 (2009) [2] E.L. Dreizin, Metal-based reactive nanomaterials, Prog Energ Combust, 35 (2009) [3] B. Van Devener, J.P.L. Perez, J. Jankovich, S.L. Anderson, Oxide-Free, Catalyst-Coated, Fuel-Soluble, Air-Stable Boron Nanopowder as Combined Combustion Catalyst and High Energy Density Fuel, Energ Fuel, 23 (2009) [4] B. Van Devener, S.L. Anderson, Breakdown and combustion of JP-10 fuel catalyzed by nanoparticulate CeO2 and Fe2O3, Energ Fuel, 20 (2006) [5] H. Tyagi, P.E. Phelan, R. Prasher, R. Peck, T. Lee, J.R. Pacheco, P. Arentzen, Increased hot-plate ignition probability for nanoparticle-laden diesel fuel, Nano Lett, 8 (2008) [6] E. Beloni, V.K. Hoffmann, E.L. Dreizin, Combustion of Decane-Based Slurries with Metallic Fuel Additives, J Propul Power, 24 (2008) [7] D. Jackson, R. Hanson, Application of an Aerosol Shock Tube for the Kinetic Studies of n-dodecane/nano-aluminum Slurries, in: 44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Hartford, CT., [8] C. Allen, G. Mittal, C.J. Sung, E. Toulson, T. Lee, An aerosol rapid compression machine for studying energeticnanoparticle-enhanced combustion of liquid fuels, P Combust Inst, 33 (2011) [9] G. Young, Metallic Nanoparticles as Fuel Additives in Airbreathing Combustion, in, University of Maryland, College Park: Mechanical Engineering., [10] G. Young, Effect of Nanoparticle Additives in Airbreathing Combustion, in: 14th AIAA/AHI Space Planes and Hypersonic Systems and Technologies Conference, Canberra, Australia, [11] B. Rotavera, A. Kumar, S. Seal, E.L. Petersen, Effect of ceria nanoparticles on soot inception and growth in toluene-oxygenargon mixtures, P Combust Inst, 32 (2009) [12] K. Kwak, C. Kim, Viscosity and thermal conductivity of copper oxide nanofluid dispersed in ethylene glycol, Korea-Aust Rheol J, 17 (2005) [13] D.X. Han, Z.G. Meng, D.X. Wu, C.Y. Zhang, H.T. Zhu, Thermal properties of carbon black aqueous nanofluids for solar absorption, Nanoscale Res Lett, 6 (2011). [14] M.J. Pastoriza-Gallego, L. Lugo, J.L. Legido, M.M. Pineiro, Thermal conductivity and viscosity measurements of ethylene glycol-based Al(2)O(3) nanofluids, Nanoscale Res Lett, 6 (2011). [15] G. Ramesh, N.K. Prabhu, Review of thermo-physical properties, wetting and heat transfer characteristics of nanofluids and their applicability in industrial quench heat treatment, Nanoscale Res Lett, 6 (2011). [16] R.A. Taylor, P.E. Phelan, T.P. Otanicar, R. Adrian, R. Prasher, Nanofluid optical property characterization: towards efficient direct absorption solar collectors, Nanoscale Res Lett, 6 (2011). [17] S. Tanvir, L. Qiao, Surface tension of Nanofluid-type fuels containing suspended nanomaterials, Nanoscale Res Lett., 7 (2012) 226. [18] Y. Gan, Y.S. Lim, L. Qiao, Combustion of Nanofluid Fuels with the Addition of Boron and Iron Particles at Dilute and Dense Concentrations, Combust Flame, (In Press). [19] Y.A. Gan, L. Qiao, Combustion characteristics of fuel droplets with addition of nano and micron-sized aluminum particles, Combust Flame, 158 (2011) [20] J.Y. Zhu, D. Dunnrankin, G.S. Samuelsen, Cars Temperature-Measurements in a Droplet Stream Flame, Combust Sci Technol, 83 (1992) [21] D. Blunck, S. Basu, Y. Zheng, V. Katta, J. Gore, Simultaneous water vapor concentration and temperature measurements in unsteady hydrogen flames, P Combust Inst, 32 (2009)