Laminar Partially Premixed Flames of Blends of Pre ...

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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

[email protected]

RAMKUMAR N. PARTHASARATHY University of Oklahoma,


[email protected]

SUBRAMANYAM R. GOLLAHALLI University of Oklahoma,


[email protected]

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

mailto:[email protected]




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.


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


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


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.


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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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.


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

International Energy Conversion Engineering

Conference.

19. Romero, D., Parthasarathy, R. N., & Gollahalli, S. R.

(2014) “Laminar Flame Characteristics of Partially

Premixed Prevaporized Palm Methyl Ester and Diesel

Flames,” Journal of Energy Resources

Technology, 136, 032204.


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


Figure 1: Experimental Setup Diagram

Figure 2: Schematic diagram of fuel/air injection system


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)


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


Figure 4b : Global NO emission index of all the flames tested

Figure 5: Radiative fraction of heat release for all the flames tested


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


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


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


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


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


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


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


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


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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