View
15
Download
0
Category
Preview:
Citation preview
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
1
8th
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 Tanvir1 and Li Qiao
1
1
School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN, 47907
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 100-500 µm and spacing
between 200-600 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 D2-Law of droplet burning.
For higher concentrations, the burning rate reduces as a function of time hence deviating
from the D2-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.
1. Introduction
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].
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
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 Al0.7Li0.3, 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 air-
breathing 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 CeO2 nanoparticles and later
boron nanoparticles coated with a CeO2 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 CeO2 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 0.5 – 2.5 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].
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
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
0.5-2.5 mm. For smaller droplets such as in a spray, however, particle aggregation may be a less-
serious 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
(100-500 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.
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
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.
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
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 800×600 and a color Photron Fastcam camera with a
speed of 1000 fps at a resolution of 512×512). A frequency of 20 kHz was used for the
preliminary combustion experiments. This gives the maximum distance (550 µm) between each
droplet of diameter ~190-200 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
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
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
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
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.
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
8
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 Al2O3 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.
(a) (b)
(c)
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
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 2.28. The higher values attributed to denser spherical
clusters and the lower to the less dense chain like aggregate structures.
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
10
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.
(a) (b)
(c)
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
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 (0.1-2.0 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
(0.1-1.0 wt.%) give an R2 (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 D2-Law for droplet combustion. The 2 wt.% case gives an R
2 value of
0.986 indicating good correlation with the D2-Law. For higher concentrations however, this is
not the case. For 3 and 4 wt. % aluminum nanofluids, the droplet size regression deviates from
the D2-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 D2-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
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
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 D2-Law of droplet burning. For higher concentration cases, the burning rate varies
throughout the entire evaporation process in situations in which the D2-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.
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
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 0.8925ms 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.
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
14
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.
2.5 inches
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
15
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 D2-
Law of droplet burning. For higher concentrations, the burning rate reduces as a function
of time hence deviating from the D2-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
2.5 inches
Paper # 070HE-0036 Topic: Heterogeneous combustion, sprays & droplets
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) 1819-1838.
[2] E.L. Dreizin, Metal-based reactive nanomaterials, Prog Energ Combust, 35 (2009) 141-167.
[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) 6111-6120.
[4] B. Van Devener, S.L. Anderson, Breakdown and combustion of JP-10 fuel catalyzed by nanoparticulate CeO2 and Fe2O3,
Energ Fuel, 20 (2006) 1886-1894.
[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) 1410-1416.
[6] E. Beloni, V.K. Hoffmann, E.L. Dreizin, Combustion of Decane-Based Slurries with Metallic Fuel Additives, J Propul Power,
24 (2008) 1403-1411.
[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., 2008.
[8] C. Allen, G. Mittal, C.J. Sung, E. Toulson, T. Lee, An aerosol rapid compression machine for studying energetic-
nanoparticle-enhanced combustion of liquid fuels, P Combust Inst, 33 (2011) 3367-3374.
[9] G. Young, Metallic Nanoparticles as Fuel Additives in Airbreathing Combustion, in, University of Maryland, College Park:
Mechanical Engineering., 2007.
[10] G. Young, Effect of Nanoparticle Additives in Airbreathing Combustion, in: 14th AIAA/AHI Space Planes and Hypersonic
Systems and Technologies Conference, Canberra, Australia, 2006.
[11] B. Rotavera, A. Kumar, S. Seal, E.L. Petersen, Effect of ceria nanoparticles on soot inception and growth in toluene-oxygen-
argon mixtures, P Combust Inst, 32 (2009) 811-819.
[12] K. Kwak, C. Kim, Viscosity and thermal conductivity of copper oxide nanofluid dispersed in ethylene glycol, Korea-Aust
Rheol J, 17 (2005) 35-40.
[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) 354-368.
[20] J.Y. Zhu, D. Dunnrankin, G.S. Samuelsen, Cars Temperature-Measurements in a Droplet Stream Flame, Combust Sci
Technol, 83 (1992) 97-114.
[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) 2527-2534.
Recommended