1 Copyright © 2014 by ASME
LAMINAR PARTIALLY PREMIXED FLAMES OF BLENDS OF PRE-VAPORIZED
JET-A FUEL AND PALM METHYL ESTER
ARUN BALAKRISHNAN University of Oklahoma,
Aerospace and Mechanical Engineering, Norman, Oklahoma, 73019, USA
RAMKUMAR N. PARTHASARATHY University of Oklahoma,
Aerospace and Mechanical Engineering, Norman, Oklahoma, 73019, USA
SUBRAMANYAM R. GOLLAHALLI University of Oklahoma,
Aerospace and Mechanical Engineering, Norman, Oklahoma, 73019, USA
ABSTRACT Biofuels, such as palm methyl ester (PME), are attractive
alternates to petroleum fuels. In order to isolate the effects of
fuel chemistry on the combustion properties, laminar partially
premixed pre-vaporized flames of blends of Jet-A and PME
(volume concentrations of 25%, 50%, 75% PME) were studied.
A stainless steel circular tube (ID of 9.5 mm) served as the
burner. The liquid fuel was supplied with a syringe pump into a
high temperature (390oC) air flow to vaporize it completely
without coking. The fuel flow rate was maintained constant and
the air flow rate adjusted to obtain burner-exit equivalence
ratios of 2, 3 and 7. The global flame properties including
flame length, CO and NO emission indices, radiative heat
fraction and in-flame properties including gas concentration
(CO, CO2, NO, O2), temperature and soot volume fraction were
measured. The near-burner homogeneous gas-phase reaction
zone increased in length with the addition of PME at all
equivalence ratios. The concentration and global emission
measurements highlight the non-monotonic variation of
properties with the volume concentration of PME in the fuel.
The fuel-bound oxygen of PME affected the combustion
properties significantly.
NOMENCLATURE
EICO = Global CO emission index
EINO = Global NO emission index
F = Radiative fraction of heat release
FL = Flame length
= Soot volume fraction
L = Distance between radiometer and flame
LHV = Lower heating value
MW = Molecular weight
= Mass flow rate of fuel
N = Number of carbon atoms in fuel
Q = Radiative heat flux from flame
χ = Mole fraction
= Equivalence ratio
Subscripts
i = Species i
f = fuel
INTRODUCTION
Jet-A is a complex mixture of alkanes (50-65% by
volume), mono and poly aromatics (10-20% by volume) and
cycloalkanes or mono-and polycyclic napthalenes (20-30 vol
%) [1]. Due to the increased gap between the production rate of
these fossil fuels and demand, along with the concern over air
quality and environment, alternate fuels are being developed.
Biofuels, such as palm methyl ester (PME), are mixtures of
monoalkyl esters of long carbon chain fatty acids that are made
from renewable feed stock (palm oil) by transesterification.
Besides being close to carbon-neutral, these biofuels have
properties similar to those of petroleum fuels and can be readily
blended with petroleum fuels and used in existing engines
without any major modifications. Furthermore, they contain
Proceedings of the ASME 2014 International Mechanical Engineering Congress and Exposition IMECE2014
November 14-20, 2014, Montreal, Quebec, Canada
IMECE2014-36930
2 Copyright © 2014 by ASME
oxygen while being free of aromatic content; therefore, blends
of biofuels and petroleum fuels present the capability of
reducing soot emissions from engines when blended with
standard jet fuels. Biofuels suffer from drawbacks, such as low
energy density, high freezing point and poor stability with time.
Test results by Corporan et al. [2] showed the potential of
biofuels to reduce soot emissions in a turbine engine without
negatively impacting the engine performance; also, these
biofuels were observed to have minimal effect on the formation
of polycyclic aromatic hydrocarbons.
A study by Kimble-Thom et al. [3] showed that the
lubricity of jet fuel was improved with even a small addition of
biofuel. Blends of biofuels and Jet-A were found to have a
higher flash point than neat Jet-A, which facilitated safer fuel
handling. The studies have also shown improved emissions
using biodiesel in aircraft engines; however, these tests
concluded that a more detailed and specific study was
necessary to determine the impact of biodiesel on the
environment and more specifically on criteria pollutants.
Dagaut et al. [1] studied the kinetics of the oxidation of a
mixture of Jet-A fuel and rapeseed oil methyl ester (80/20 on
molar basis) in a stirred reactor at 10 atm and constant
residence time, over the temperature range of 740 - 1200 K.
The calculations showed that the biofuel blend had a slightly
higher reactivity than that of neat Jet A fuel; also, no major
modification of the product distribution was observed.
A few studies have been conducted on the performance and
emissions of engines fueled with PME and PME blends.
Hashimoto et al. [4] evaluated PME as an alternative fuel for
gas turbine engines. Chemical equilibrium calculations
indicated that there was no significant difference in the
adiabatic flame temperature of petroleum diesel and PME.
Experiments were carried out in spray flames of diesel and
PME with the viscosity matched by pre-heating PME. It was
found that the NOx emissions from the PME spray flames were
lower than those of diesel flames. Sharon et al. [5] ran tests in a
direct injection diesel engine with blends of diesel and PME
and found that the CO and soot emissions were lower with the
PME blends, but the NOx emissions were higher.
OBJECTIVE The aforementioned studies do not delineate the effects of
chemical structure of the fuel alone due to the complexities of
atomization, vaporization, turbulence and high pressure that
occur in an engine. In our laboratory, a method has been
developed to characterize the combustion characteristics
attributable only to the molecular structure of the fuel [6]. The
liquid fuel is pre-vaporized in hot air and the fuel/air mixture is
burned in a laminar flame. The results obtained using this
method for canola methyl ester (CME) and soy methyl ester
(SME) agreed well with those measured during combustion in
engines [7 – 9].
The objective of this study is to document the combustion
properties of blends of pre-vaporized PME and Jet-A fuel in the
laminar flame environment developed previously [6] in order to
understand the effects of fuel molecular structure on the
combustion characteristics. The particular objectives were to
measure (a) visual flame length (b) global emissions, (c) flame
radiation, (d) in-flame gas concentration profiles, (e) in-flame
temperature profiles and (f) soot volume concentration
variation in laminar flames of Jet-A/PME blends at injector exit
equivalence ratios of 2, 3 and 7. These initially fuel-rich
conditions were chosen to simulate the various reaction zones
that exist in a diesel engine [10].
EXPERIMENTAL SETUP AND INSTRUMENTATION
EXPERIMENTAL SETUP A schematic diagram of the setup is presented in Figure 1.
The experiments were conducted in a large steel combustion
chamber (76 cm by 76 cm and 150 cm in height). The burner
used for the experiments was housed within the chamber at its
bottom center. The walls of the chamber contained high-
temperature glass windows provided with removable slotted
metal sheet covers measuring 96 cm x 25 cm to allow optical
access. The top of the combustion chamber was open to
atmosphere through an exhaust duct. The ambient pressure of
the laboratory was maintained at slightly above the atmospheric
pressure (~20 Pa) to provide a positive draft inside the test
chamber to prevent leakage of the combustion products into the
laboratory. A stainless steel circular tube (ID of 9.5 mm and OD
of 12.7 mm, Fig. 2) with a beveled rim served as the burner.
This burner provided a stable laminar flame and is described in
in previous studies [6 - 9].
In order to vaporize the fuel completely without liquid-
phase pyrolysis that could lead to coking of the fuel, the liquid
was injected into a high-temperature air stream. The air flow
was provided in a 12.7 mm (OD) steel feed line tubing with
heating tape wrapped around it. The heating tape was connected
to a proportional temperature controller which was
continuously monitored; the air temperature upstream and
downstream of the fuel injection location were measured with
K-type thermocouples embedded in the feed line and were also
monitored. The air flow temperature at the fuel injection
location was maintained at 390oC, which was sufficiently high
above the final boiling point of the fuels so as to completely
vaporize the injected fuel and low enough to prevent coking in
the feed lines. The heated line was long enough (230 cm) to
ascertain that the liquid fuel was completely vaporized in the
air stream before exiting the burner. The liquid fuel was
delivered to the heated air (supplied from a compressed air
tank) through a high temperature silica-based septum with a 50
cm3 capacity syringe attached to a syringe pump. A periodic
examination of the tube walls indicated the absence of any
coking. Also, experiments with an air/fuel ratio analyzer
indicated that the entire mass flow of liquid fuel injected into
the heated air stream exited the burner in vapor state (based on
the carbon balance). The volume flow rate of air was monitored
using a calibrated rotameter. The fuel-air mixture was ignited at
the exit of the burner with an external pilot flame which was
removed after ignition.
3 Copyright © 2014 by ASME
The properties of the tested fuels are presented in Table 1.
Three blends of PME and Jet A with volume concentrations 25,
50 and 75% of PME (designated as P25, P50 and P75
respectively) were studied in addition to PME and Jet-A. Neat
PME, designated as P100, has significant oxygen content
(about 11.9% by mass) compared to Jet A. The lower heating
value of PME is about 10% less than that of Jet A. Thus, as the
volume concentration of PME is decreased, the oxygen content
in the fuel is reduced and the heating value goes up.
The test conditions are presented in Table 2. The fuel flow
rate was held constant and the air flow rate was altered to result
in burner-exit stoichiometric ratios of 2, 3 and 7. The burner
exit Reynolds number (based on the bulk velocity of fuel-air
mixture, mixture density, viscosity and inner diameter of the
tube) was in the range of 400 – 1000, indicating laminar flow
which was confirmed by the visual appearance of the flame.
The modified Froude number values [11] were in the range of
0.09 – 0.8, indicating that the flames were in the regime
designated as turbulent buoyant near the top. The major
portions of the flames appeared to have smooth edges except
near the very top. Most of the primary effects of the fuel
chemistry occur in the near-burner (pyrolysis) and mid-flame
(gas-phase oxidation and soot growth) regions; only soot
burning is significant near the top. Thus, the present flame
configuration could be used to compare the fuel chemistry
effects. Also, the present flames were partially-premixed, with
substantial amount of air supplied with the fuel. The
applicability of the modified Froude number, as defined by
Delichatsios [11] for only fuel jet flames, which includes the
stoichiometric air-fuel ratio (assuming that all the required air
was entrained from the surroundings) for the present flames is
debatable.
FLAME VISUALIZATION Flame images were obtained at similar lighting and
exposure conditions with an exposure time of 1 s. The flame
length was calculated by measuring the number of pixels
between the burnet exit and the farthest visible point of the
luminous flame and the number of pixels was converted into
equivalent length scale using a known reference. Three images
per condition were captured and the resultant flame lengths
were averaged.
GLOBAL EMISSION MEASUREMENT A pyrex funnel with a height of 27 cm, bottom diameter of
16 cm and top diameter of 4 cm was mounted above the flame,
where the flue gases were collected and guided to an uncooled
quartz probe with a 1 mm inner diameter orifice that rapidly
expanded to 4 mm (inner diameter). These gas samples were
passed through a water condenser immersed in an ice bath, in
order to report all the emissions results on a dry basis and to
remove any moisture, and subsequently were directed through a
fiber filter to trap particulate matter. Measurements of the
volumetric concentration of CO, CO2 and NOx in the exhaust
were carried out using a portable gas analyzer. The analyzer
consisted of a built-in infrared detector for CO and CO2
concentration measurements and electrochemical sensors for
the measurement of O2 and NOx concentrations.
The measurements were converted into emission indices
on a mass basis (g of species/kg of fuel) [12]. The emission
index is the mass of pollutant produced per unit mass of fuel
burned independent of any dilution of the product stream. The
emission index is expressed as:
𝐸𝐼𝑖 = (𝜒𝑖
𝜒𝑐𝑜+𝜒𝑐𝑜2) (
𝑁∗𝑀𝑊𝑖
𝑀𝑊𝑓𝑢𝑒𝑙) ∗ 1000 (1)
where 𝜒𝑖, 𝜒𝑐𝑜 and 𝜒𝑐𝑜2 are the mole fraction of the species,
CO and CO2 respectively, N is the number of atoms of carbon
in a mole of fuel, and 𝑀𝑊𝑖 and 𝑀𝑊𝑓𝑢𝑒𝑙 are the molecular
weights of the species, i and fuel respectively. It is assumed that
all the carbon in the fuel is converted into CO and CO2 with
negligible amounts of soot. This assumption was found to be
valid since the flames tested were not smoking enough to
produce significant amount of solid carbon in the exhaust.
RADIATION MEASUREMENT A wide view-angle (150
0) high sensitivity pyrheliometer
with quartz window was used to measure the total radiation
from the flame. The pyrheliometer had a linear output with a
responsivity of 44.56 mV per kW/m2 and was located far
enough (50 cm) from the burner so that its view-angle covered
the entire flame length and the flame could be assumed as a
point source. The measured radiative heat flux was sampled at
1 Hz for time duration of 3 minutes using LabView software.
The background radiation was subtracted from the total
radiation to obtain the flame radiation, and was expressed as the
radiative fraction of heat release, F:
= 4𝜋 𝐿2 𝑄
�� 𝐿𝐻𝑉 (2)
Here, L is the distance from the flame centerline to the
pyrheliometer, Q is the corrected radiative heat flux measured,
ṁ is the mass flow rate of the liquid fuel and LHV is the lower
heating value of the liquid fuel tested. The radiative fraction of
heat release is the fraction of the heat content of the fuel that is
lost as radiation from the flame due to gas band radiation and
gray-body radiation from soot particles.
IN-FLAME CONCENTRATION MEASUREMENT
The in-flame gas concentration measurements were
performed using a stainless steel sampling probe (1.75 mm ID
and 3.2 mm OD); the diameter of the sampling probe was large
enough to prevent clogging due to soot accumulation. The gas
samples were treated to remove the moisture and particulates
before sending them into a portable flue gas analyzer that was
used for the global emission measurement. The sampling probe
was mounted on a two-dimensional linear traverse mechanism
which facilitated the axial and radial movement of the probe
across the flame field. Measurements were taken at 2 mm radial
4 Copyright © 2014 by ASME
distance intervals at three different heights corresponding to
25%, 50% and 75% of the visible flame length.
IN-FLAME TEMPERATURE MEASUREMENT The in-flame temperature profiles were measured using an
R-Type (Pt-Pt/13% Rh) thermocouple with a bead diameter of
0.2 mm. Catalytic action was reduced by coating the tip of the
thermocouple with a fine layer of silica. The thermocouple was
positioned along the length of the flame using a manually-
guided traverse mechanism. Data acquisition was accomplished
using LabView software. The temperature readings were
averaged over a period of 30 seconds with 1Hz of sampling rate
and corrected for radiation and conduction losses [13].
SOOT VOLUME CONCENTRATION MEASUREMENT The path-integrated soot volume fraction was measured
using laser attenuation with Beer’s law and Mie scattering
theory, as presented by Yagi and Iino [14]. The soot volume
fraction was computed [15] using equation (3):
= −𝑙𝑛(
𝐼0𝐼𝑠)𝜆
𝑘𝜆𝛿 (3)
where Is and Io are the incident and attenuated laser intensities
respectively; kλ is the spectral extinction coefficient based on
the refractive indices of the soot; λ is the employed laser
wavelength and δ is flame thickness (beam path) obtained from
photographs. The spectral extinction coefficient (kλ) was
assumed to be constant, corresponding to that of diesel soot.
Previous measurements have indicated that the refractive index
of diesel soot was not significantly different from that of the
soot formed in soy methyl ester flames [16]. A 5 mW Helium
Neon laser (λ = 632.8 nm) was used as a light source with a
power detector. The voltage readings from the power detector
were digitally sampled at the rate of 10 Hz for 30 seconds using
LabView software. The beam attenuation due to the presence of
soot was obtained by measuring the intensity of light with and
without flame field. The burner remained stationary, with the
laser and power detector aligned on a traversing mechanism to
obtain radial and axial profiles.
RESULTS AND DISCUSSION FLAME APPEARANCE
Color photographs of the flames are presented in figures 3a
-3c for burner exit equivalence ratios of 2, 3 and 7. Two
primary regions were observed in the flames: a bright blue
lower region (< 10 cm) and a more luminous upper yellow
region. The lower bright blue region was composed of an inner
luminous cone surrounded by an outer less luminous region.
This inner cone represented the primary gas-phase oxidation
reaction zone with the enveloping outer region consisting of
the unburned reactants in the surrounding flame zone that
mixed with the ambient air. The upper yellow region was
dominated by soot that continued to burn and mix with ambient
air downstream of the burner tip. At all conditions, as the PME
content in the fuel was increased, the near-burner blue region
increased in size due to the presence of the oxygen in the fuel. At the equivalence ratio of 2, Jet A flames were the longest
(23 cm), whereas the other flames were of comparable length
(15-18 cm). In the present experiments, the equivalence ratio
was increased by reducing the amount of supplied air, thus
more air from the surroundings needed to be entrained,
requiring an increase in length to effectively burn remaining
fuel or particulates. At the equivalence ratio of 3, the Jet-A
flames were the longest (26 cm), whereas the P75 and P100
flames were the shortest (16 cm). The Jet-A and P25 flames
has a significant reduction in length at the equivalence ratio of
7 because the maximum sooting flame height was reached
between equivalence ratios of 3 and 7.
GLOBAL EMISSIONS The global CO emission index is presented in Figure 4a.
The global CO emission index increased with equivalence ratio
for all the fuels tested because less air was supplied at higher
equivalence ratios resulting in incomplete combustion. At =
2 and 3, the P50 flames had the lowest global CO emission
index values. The increase in the global CO emission index in
the flames of P75 and PME could be due to the oxidation of
soot in the far-burner regions and the quenching of CO to CO2
reactions. At = 7, a dramatic decrease in the CO emission
index value was observed with the increase in PME content. A
reduction of about 30% was observed going from Jet-A to P25
flames, and another reduction of 25% was seen between the
P25 and P50 flames, and between the P50 and P75 flames. The
CO emission index of the P100 flames was comparable to that
of the P75 flames. The effect of fuel-bound oxygen on the CO
emission index was significant at this equivalence ratio.
The global emission index of NO is presented in Figure 4b.
As the equivalence ratio was increased, the NO emission index
decreased due to the significant decrease in flame temperature
for all the fuels tested (to be discussed subsequently). The
variation of NO emission index with PME concentration was
non-monotonic. At = 2 and 3, the P100 flames had the lowest
NO emission index, whereas the P50 and P75 flames had the
lowest NO emission index at the equivalence ratio of 7. Such
non-monotonic behavior with biofuel concentration has been
observed in similar flames of diesel/canola methyl ester blends
[9].
RADIATIVE HEAT FRACTION The radiative fraction of heat release for all the fuels tested
is presented in Figure 5. The radiative fraction increased
significantly as the equivalence ratio was increased due to the
increase in soot content of the flame (as seen in the increasing
luminosity in the photographs in Figures 3a – 3c and confirmed
by soot volume concentration measurements). At = 2 and 3,
the radiative fraction was comparable between the flames of the
neat fuels with a slight decrease in the flames of the blends. A
substantial reduction in the radiative fraction was observed with
an increase in PME content at = 7. This was due to the lower
5 Copyright © 2014 by ASME
amount of soot content (as confirmed by the soot volume
concentration measurements) in the flames of PME blends at
this condition. The result is more conspicuous at this
equivalence ratio due to high soot content of the flames.
IN-FLAME TEMPERATURE PROFILES The radial temperature profiles at 25%, 50% and 75% of
the flame height of all the blend flames (P25, P50 and P75) are
presented at the three equivalence ratios in Figures 6 - 8. The
peak temperatures at 25% flame height were comparable for the
different fuels at the same equivalence ratio. At an equivalence
ratio of 2, the temperature profiles in the near-flame region
exhibited a double hump, indicating that the primary reaction
zone was located slightly away from the centerline. The
maximum value shifted to the centerline by mid flame height
due to entrainment and mixing. At 75% flame height, the
temperature in the P25 flames was lower than that of the P50
and P75 flames. As the equivalence ratio was increased, the
peak temperature was reduced due to the reduction in the
supplied air. Again, at 75% flame length, the temperature
recorded in the P50 and P75 flames was comparable and higher
than that of the P25 flames. At = 7, the temperature values
were comparable for all the flames at all heights.
The differences in the diameter of soot particles and the
opposing effects of soot burning and radiative loss from the
soot particles could have a significant influence on temperature.
Previous studies have shown that the soot particles formed in
canola methyl ester flames were one-half the size of diesel soot
and those formed in soy methyl ester flames were about 70%
the size of diesel soot [17]. Additional work on the knowledge
of the properties of soot particles formed during the combustion
of PME/Jet-A blends is needed to better understand these flame
properties.
IN-FLAME GAS CONCENTRATIONS The oxygen concentration at 25%, 50% and 75% flame
heights is presented in Figures 9 -11. The oxygen concentration
was low near the centerline and increased to the ambient value
towards the edge. In general, the oxygen concentration near the
centerline increased with downstream distance due to
entrainment of surrounding air. The oxygen concentration
measured near the centerline was comparable for all the flames.
The total oxygen supplied at the injector exit (fuel-bound or
premixed) was the same for all the fuels for a given equivalence
ratio. The variation in oxygen concentration levels may be due
to the differences in air diffusion (due to slightly different
injector exit velocities and diffusion coefficients) and oxygen
reaction mechanisms.
The CO2 concentration at 25%, 50% and 75% flame
heights is presented in Figures 12 - 14. As the equivalence ratio
was increased and less air was supplied, the peak CO2
concentration decreased. The CO2 concentration levels were
comparable in all the flames at a given equivalence ratio. It is
interesting to note that the highest CO2 concentration occurred
at mid-flame height for the P50 and P75 flames, whereas the
highest CO2 concentration was at 25% flame height for the P25
flames at the equivalence ratio of 2. The CO2 concentration in
the far-flame region for the P50 and P75 flames was lower than
that measured in the P25 flames at equivalence ratios of 3 and
7.
The CO concentration at 25%, 50% and 75% flame heights
is presented in Figures 15 - 17. Carbon monoxide is produced
from the partial oxidation of carbon-containing compounds.
The peak CO concentration occurred at 25% flame height and
decreased with flame height. At = 2, the CO concentration in
the P25 flames was higher than that of the P50 and P75 flames;
the CO concentration of the P50 and P75 flames was higher
than that of the P25 flames at the equivalence ratio of 3. At =
7, CO concentration was comparable between all the flames.
This non-monotonic variation has been observed in the flames
of other biofuels previously. The complex competition of soot
growth and oxidation rates and their dependence on fuel iodine
number could cause this variation.
The NO concentration profiles, displayed in Figures 18 –
20 indicate that the peak NO concentration occurred at 25%
flame height, where the peak flame temperature was reached
(Figures 6 – 8). At = 2 and 25 % flame height, the P75 flames
had significantly higher NO concentration than the P25and P50
flames even though the temperature was comparable (Figure 6).
At = 3 and 25% flame height, the NO concentration of P50
and P75 flames was comparable and higher than that of the P25
flames. However, at = 7 and 25% flame height, the NO
concentration of the P75 flames was significantly lower than
that of the other flames. Further studies are needed to delineate
this non-monotonic effect with blend ratio.
The concentration measurements also highlight the non-
monotonic variation of the combustion properties of biofuel
blends with the concentration of biofuel. Detailed CH and OH
radical measurements are needed to further understand the
formation of NO in these flames, which are currently in
progress at the authors’ laboratory.
SOOT VOLUME CONCENTRATION The path-integrated soot volume concentration distribution
at 25, 50 and 75% flame height is presented in Figures 21 – 23.
At = 2, the soot volume concentration levels observed at 75%
of flame height was significantly higher than that at 25 and
50% flame height due to significant particle agglomeration and
growth. As the equivalence ratio was increased, the soot content
in the flames increased. Note that the carbon input rate was
constant for the present conditions (Table 2). The equivalence
ratio was increased by reducing the amount of coflow air. The
increase in soot content was due to the reduction in the
available oxygen (in the form of supplied air). The size of the
soot particles and their morphology could influence the
refractive index, which would change the attenuation
coefficient; documentation of properties of soot formed during
the combustion of biofuel blends is planned in the future.
6 Copyright © 2014 by ASME
CONCLUSIONS In summary, the combustion characteristics of blends of
pre-vaporized PME and Jet-A fuel were studied at initial
equivalence ratios of 2, 3 and 7 in a laminar environment.
Based on the results obtained from the measurements, the
following conclusions were drawn:
(a) The flame images indicated the presence of near-burner
blue region, which was dominated by the homogeneous
gas-phase reactions. This region increased with the
concentration of PME in the fuel for all equivalence ratios
due to the increase in the oxygen content of the fuel. The
flames appeared more luminous at higher equivalence
ratios due to the increase in the soot content.
(b) The CO emission index increased with equivalence ratio
due to the reduction in the air supplied; the NO emission
index decreased with equivalence ratio due to a reduction
in the flame temperature. Both CO and NO emission
indices varied non-monotonically with the concentration of
PME in the blend. .
(c) The radiative fraction of heat release increased with
increase in equivalence ratio due to the lesser availability
of air for combustion and the increased soot formation.
This radiative fraction decreased with the PME content in
the fuel at = 7; at equivalence ratios of 2 and 3, the
flames of PME blends had lower radiative fraction values
than those of the flames of pure fuels.
(d) Peak temperatures were recorded at the equivalence ratio
of 2 and the values were comparable for all the flames. As
the equivalence ratio was increased, the peak temperatures
were significantly reduced. Significant differences in the
temperatures of the flames of the blends were observed,
possibly due to differences in the soot particle properties.
(e) The CO, CO2, NO and soot-volume concentration
measurements highlighted the non-monotonic behavior of
the combustion properties of the PME blends with the
concentration of PME. The soot volume concentration
increased with equivalence ratio due to the lower amount
of air supplied.
ACKNOWLEDGEMENTS The financial assistance provided by US Department of Energy
and NSF EPSCoR is gratefully acknowledged.
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Validation,” SAE Paper 1999-01-0509, 1-14.
11. Delichatsios, M. A. (1993) “Transition from
Momentum to Buoyancy-Controlled Turbulent Jet
Diffusion Flames and Flame Height Relationships,”
Combustion and Flame, 92, 349-364.
12. Turns, S. (2011) An Introduction to Combustion. Third
Edition, McGraw Hill, New York.
13. Jha, S. K., Fernando, S., & To, S. D. (2008) “Flame
Temperature Analysis of Biodiesel Blends and
Components,” Fuel, 87(10), 1982-1988. 14. Yagi, S., & Iino, H. (1962) “Radiation from Soot
Particles in Luminous Flames,” Eighth International
Symposium on Combustion, The Combustion Institute,
pp. 288-293. 15. Bryce, D., Ladommatos, N., & Zhao, H. (2000)
“Quantitative Investigation of Soot Distribution by
Laser-Induced Incandescence,” Applied Optics, 39,
5012-5022.
7 Copyright © 2014 by ASME
16. Choi, Seuk Cheun. (2009) “Measurement and Analysis
of the Dimensionless Extinction Constant for Diesel
and Biodiesel Soot: Influence of Pressure, Wavelength
and Fuel-type,” Ph.D. Dissertation, Department of
Mechanical Engineering and Mechanics, Drexel
University, Philadelphia, PA. 17. Merchan-Merchan, W., Sanmiguel, S. G., &
McCollam, S. (2012) “Analysis of Soot Particles
Derived from Biodiesels and Diesel Fuel Air-Flames,”
Fuel, 102, 525-535. 18. Grisanti, M., Parthasarathy, R., & Gollahalli, S. (2011)
“Physical and Combustion Properties of Biofuels and
Biofuel Blends with Petroleum Fuels,” 9th Annual
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19. Romero, D., Parthasarathy, R. N., & Gollahalli, S. R.
(2014) “Laminar Flame Characteristics of Partially
Premixed Prevaporized Palm Methyl Ester and Diesel
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8 Copyright © 2014 by ASME
Table 1: Properties of tested fuels
Fuel
Equivalent
Molecular
Formula
Density Molecular
weight
Kinematic
Viscosity
Lower
Heating
Value
Oxygen
Content
Boiling
Point
(kg/m3) (g/gmol) (cSt) (MJ/kg) (% wt.) (
0C)
JetAa
C13 H23 802 179 1.79 42.80 0 145-300
P25c C13.79H24.93O0.39 814.1 196.7 2.35 40.89 3.2 -
P50c C14.7H27.16O0.84 832.3 217 3 39.26 6.2 -
P75c C15.77H29.78O1.37 850.4 240.9 3.78 37.89 9.1 -
P100b C17.05 H32.90 O2 868.5 268.7 4.71 36.77 11.9 350-354
a Grisanti.et al [18] & Turns [11],
b Romero.et al [19] & Hyperfuels B100 (2006),
c estimated values
Table 2: Test Conditions
Fuel Equivalence
Ratio (Φ)
(A/F)Stoic
by Mass
Carbon mass
fraction in fuel
Fuel flow
rate (m3/s)
Carbon input
rate (kg/s)
Air Flow Rate
(m3/s)
Jet A
2
14.38 0.872
3.67x10-8
2.57x10-5
17.4x10-5
3 11.6x10-5
7 4.98x10-5
P25
2
13.84 0.841 2.51x10-5
17.2x10-5
3 11.5x10-5
7 4.92x10-5
P50
2
13.33 0.796 2.43x10-5
16.9x10-5
3 11.3x10-5
7 4.84x10-5
P75
2
12.84 0.785 2.45x10-5
16.7x10-5
3 11.1x10-5
7 4.77x10-5
P100
2
12.37 0.761 2.43x10-5
16.4x10-5
3 10.9x10-5
7 4.67x10-5
9 Copyright © 2014 by ASME
Figure 1: Experimental Setup Diagram
Figure 2: Schematic diagram of fuel/air injection system
10 Copyright © 2014 by ASME
Figure 3a : Flame images at equivalence ratio of 2 (Exposure time of 1/25 seconds)
Figure 3b : Flame images at equivalence ratio of 3 (Exposure time of 1/25 seconds)
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Figure 3c : Flame images at equivalence ratio of 7 (Exposure time of 1/25 seconds)
Figure 4a : Global CO emission index of all the flames tested
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Figure 4b : Global NO emission index of all the flames tested
Figure 5: Radiative fraction of heat release for all the flames tested
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Figure 6a : Radial temperature profiles of P25 flames at Φ = 2 Figure 6b : Radial temperature profiles of P50 flames at Φ = 2
Figure 6c : Radial temperature profiles of P75 flames at Φ = 2 Figure 7a : Radial temperature profiles of P25 flames at Φ = 3
Figure 7b : Radial temperature profiles of P50 flames at Φ = 3 Figure 7c : Radial temperature profiles of P75 flames at Φ = 3
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Figure 8a : Radial temperature profiles of P25 flames at Φ = 7 Figure 8b : Radial temperature profiles of P50 flames at Φ = 7
Figure 8c : Radial temperature profiles of P75 flames at Φ = 7 Figure 9a : O2 concentration profiles of P25 flames at Φ = 2
Figure 9b : O2 concentration profiles of P50 flames at Φ = 2 Figure 9c : O2 concentration profiles of P75 flames at Φ = 2
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Figure 10a : O2 concentration profiles of P25 flames at Φ = 3 Figure 10b : O2 concentration profiles of P50 flames at Φ = 3
Figure 10c : O2 concentration profiles of P75 flames at Φ = 3 Figure 11a : O2 concentration profiles of P25 flames at Φ = 7
Figure 11b : O2 concentration profiles of P50 flames at Φ = 7 Figure 11c : O2 concentration profiles of P75 flames at Φ = 7
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Figure 12a : CO2 concentration profiles of P25 flames at Φ = 2 Figure 12b : CO2 concentration profiles of P50 flames at Φ = 2
Figure 12c : CO2 concentration profiles of P75 flames at Φ = 2 Figure 13a : CO2 concentration profiles of P25 flames at Φ = 3
Figure 13b : CO2 concentration profiles of P50 flames at Φ = 3 Figure 13c : CO2 concentration profiles of P75 flames at Φ = 3
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Figure 14a : CO2 concentration profiles of P25 flames at Φ = 7 Figure 14b : CO2 concentration profiles of P50 flames at Φ = 7
Figure 14c : CO2 concentration profiles of P75 flames at Φ = 7 Figure 15a : CO concentration profiles of P25 flames at Φ = 2
Figure 15b : CO concentration profiles of P50 flames at Φ = 2 Figure 15c : CO concentration profiles of P75 flames at Φ = 2
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Figure 16a : CO concentration profiles of P25 flames at Φ = 3 Figure 16b : CO concentration profiles of P50 flames at Φ = 3
Figure 16c : CO concentration profiles of P75 flames at Φ = 3 Figure 17a : CO concentration profiles of P25 flames at Φ = 7
Figure 17b : CO concentration profiles of P50 flames at Φ = 7 Figure 17c : CO concentration profiles of P75 flames at Φ = 7
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Figure 18a : NO concentration profiles of P25 flames at Φ = 2 Figure 18b : NO concentration profiles of P50 flames at Φ = 2
Figure 18c : NO concentration profiles of P75 flames at Φ = 2 Figure 19a : NO concentration profiles of P25 flames at Φ = 3
Figure 19b : NO concentration profiles of P50 flames at Φ = 3 Figure 19c : NO concentration profiles of P75 flames at Φ = 3
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Figure 20a : NO concentration profiles of P25 flames at Φ = 7 Figure 20b : NO concentration profiles of P50 flames at Φ = 7
Figure 20c : NO concentration profiles of P75 flames at Φ = 7 Figure 21a : Soot concentration profiles of P25 flames at Φ = 2
Figure 21b : Soot concentration profiles of P50 flames at Φ = 2 Figure 21c : Soot concentration profiles of P75 flames at Φ = 2
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Figure 22a : Soot concentration profiles of P25 flames at Φ = 3 Figure 22b : Soot concentration profiles of P50 flames at Φ = 3
Figure 22c : Soot concentration profiles of P75 flames at Φ = 3 Figure 23a : Soot concentration profiles of P25 flames at Φ = 7
Figure 23b : Soot concentration profiles of P50 flames at Φ = 7 Figure 23c : Soot concentration profiles of P75 flames at Φ = 7
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