DSpace at VNU: Experimental investigation of the effects of cycloparaffins and aromatics on the sooting tendency and the freezing point of soap-derived biokerosene and normal paraffins

Fuel 185 (2016) 855–862

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Fuel
journal homepage: www.elsevier.com/locate/fuel

Full Length Article

Experimental investigation of the effects of cycloparaffins and aromatics
on the sooting tendency and the freezing point of soap-derived
biokerosene and normal paraffins
Long H. Duong a,d, Osamu Fujita b,⇑, Iman K. Reksowardojo a, Tatang H. Soerawidjaja c, Godlief F. Neonufa c
a

Combustion Engines and Propulsion Systems Laboratory, Faculty of Mechanical and Aerospace Engineering, Institut Teknologi Bandung, Bandung 40132, Indonesia
Division of Mechanical and Space Engineering, Hokkaido University, Sapporo 060-8628, Japan
Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Bandung, Bandung 40132, Indonesia
d
Department of Automotive Engineering, Faculty of Transportation Engineering, Ho Chi Minh City University of Technology, Ho Chi Minh City 70350, Viet Nam
b
c

a r t i c l e

i n f o

Article history:
Received 1 May 2016
Received in revised form 10 August 2016
Accepted 12 August 2016

Available online 19 August 2016
Keywords:
Soap-derived biokerosene
Sooting tendency
Freezing point
Normal paraffins
Cycloparaffins
Aromatics

a b s t r a c t
The effects of cycloparaffin and aromatic hydrocarbons when blended with soap-derived biokerosene
(SBK) and normal paraffins (n-paraffins) on the sooting tendency and the freezing point are quantified
to determine a method for improving the properties of SBK and n-paraffin fuels. In this study, SBK was
derived from the saponification and dercarboxylation of coconut oil, and consists predominantly of
n-paraffins with carbon chain lengths from C7 to C17. Dodecane, butylcyclohexane and butylbenzene
were chosen as surrogate components for n-paraffins in SBK, cycloparaffins and aromatics, respectively.
The total soot volume was measured from the light extinction at ambient conditions in a wick-fed laminar diffusion flame. The measured smoke point of the fuel was correlated with the required sooting tendency according to the jet fuel standard. The freezing point was measured using the JIS K2276 test
method. The results show that butylcyclohexane affects the sooting tendency much lesser than butylbenzene when blended with SBK or dodecane. In contrast, butylcyclohexane decreases the freezing point
more, as compared to butylbenzene, when blended with dodecane. Butylcyclohexane and butylbenzene
have a similar trend of effect on the freezing point when blended with SBK or dodecane. Blending SBK or
dodecane with butylcyclohexane matches the requirements of both smoke point and freezing point for
jet fuel specified by ASTM D1655. Conversely, blending SBK or dodecane with butylbenzene does not
meet these requirements. Therefore, given the tradeoff between sooting tendency and freezing point,
cycloparaffins are considered more promising than aromatics for blending with SBK or n-paraffin fuels.
Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction
Air transportation in the modern world is rapidly growing in
popularity due to an increasing demand for business and leisure
travel. As a result, the worldwide commercial jet fleet is expected

to increase by approximately 102% [1], and the estimated annual
average growth rate of world traffic is 4.6% for the next 20 years
(2014–2034) [2]. Consequently, the jet fuel demand and the subsequent exhaust gas emissions will increase. Currently, jet fuel prices
fluctuate as they depend not only on the availability of crude oil
obtained from fossil fuels but also on many societal, economical,
and, especially, political factors. These fluctuations in the price of
jet fuels create many serious problems for airline companies,
⇑ Corresponding author at: Division of Mechanical and Space Engineering,
Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo 060-8628, Japan.
E-mail address: (O. Fujita).
/>0016-2361/Ó 2016 Elsevier Ltd. All rights reserved.

because the fuel cost represents up to 30% of an airline’s operating
cost and it is expected to increase [3]. In addition, the airline sector
is currently responsible for approximately 3% of the total global
greenhouse gas (GHG) emissions. Although this value represents
a small fraction of the total GHG emissions, aircraft emissions continue to increase and are expected to constitute nearly 5%, even
could reach up to 15% of global GHG emissions by 2050 [4]. In an
effort to reduce GHG emissions and meet the European environmental goals for 2020 and beyond, the European Union has implemented the Directive 101/2008/EC [5] since 2012. According to this
legislation, all aircrafts flying within or into the European Economic Area must either decrease their GHG emissions or purchase
CO2 allowances. Therefore, the commercial aviation industry faces
billions of US dollars in cost to pay for the carbon emission tax [6].
To reduce GHG emissions, some efforts have been applied such as
improvement of fuel consumption efficiency by increasing engine


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L.H. Duong et al. / Fuel 185 (2016) 855–862

efficiency, aircraft structure designing, and optimizing air traffic
management. Along with those methods, using biofuel is increasingly considered by airline companies and governments because
biofuel is a renewable resource and significantly reduces the lifecycle CO2 emissions [7,8]. Besides, using aviation biofuel may
reduce the pollutant emissions, such as carbon monoxide,
unburned hydrocarbon, nitrogen oxides, and soot emission, from
engines [11–15]. Currently, certain types of aviation biofuels have
been approved by the American Society for Testing Materials
(ASTM) for blending with conventional jet fuel to use in aviation
gas turbine engines. These include synthesized paraffinic kerosine
from hydroprocessed esters and fatty acids, Fischer–Tropsch
hydroprocessed synthesized paraffinic kerosine from biomass, synthesized iso-paraffins from hydroprocessed fermented sugars, synthesized kerosene with aromatics derived by alkylation of light
aromatics from non-petroleum resources, and alcohol-to-jet synthesized paraffinic kerosene. The detailed requirements of their
composition and properties are presented in ASTM D7566 [9].
Tropical countries, in general, and Indonesia, in particular, are
the ideal location for developing ground-used and aviation biofuel
because of the abundance of plant oil resources, the vast rural
areas, and the low labor cost. Moreover, the Indonesian government approved a plan to use up to 2%, 3%, and 5% by volume of aviation biofuel during flights by 2016, 2018, and 2025, respectively
[8]. However, Indonesia faces significant challenges to produce aviation biofuel due to the limitation in technology and investment.
Therefore, production of aviation biofuel based on simple technologies at a low cost, and leveraging the available national advantages is a foreseeable solution. The production of soap-derived
biokerosene (SBK) meets the above criteria, because it primarily
uses a simple production process as shown in Fig. 1. SBK production comprises of two main steps: (1) the saponification process,
through which plant oil fatty acids and triglycerides are converted
into basic-soap and (2) the subsequent thermal decarboxylation
process reacted at 275 °C and ambient pressure, through which
the basic-soap is transformed into normal-paraffins (n-paraffins).
Thereby, SBK production is simpler and less energy consumption
than the hydtrotreating processes, which are reacted at high temperature and pressure with the presence of catalyst and hydrogen,
in the common aviation biofuel productions (Fig. 2) to convert the
plant oils or animal fats into n-paraffins [10]. Furthermore, in common aviation biofuel production pathways [12,30,31], because the
fuel used in aviation gas turbine engines is required to have a very

low freezing point [16,17], the n-paraffins are generally isomerized
into branched paraffins (iso-paraffins), which have a significantly
lower freezing point. Besides, in order to improve the other properties of aviation biofuels, especially, distillation, the cracking process is also implemented to break the long carbon chain that
exceeds the jet range into shorter chain length paraffins. A typical
production process of this type of aviation biofuel is presented in
Fig. 2. However, the isomerization and cracking processes are complicated and costly [18–20]. Hence, substitution with other appropriate solutions based on the feedstock conditions, the available
technology, and the socioeconomic situation in Indonesia is
encouraged. Thereby, to avoid the cracking process in the SBK production, the plant oils that have carbon chain length of fatty acids
dominantly in jet rang (C8–C16 [16,17]) are selected as feedstock.
Besides, mixing SBK with other bio-derived components that have
low freezing points is a potential alternative to the isomerization

Coconut
Oil

Saponification
process

Basic
Soaps

process to reduce the freezing point of the biofuel. Mixed biofuels
with products of different production processes is also promising
[21] because it helps to optimize the utilization of flexible feedstock and suitable facilities to produce biofuels, thus maximizing
the national potential to develop a sustainable aviation biofuel in
each country. Currently, there are many approaches to produce
aromatics or cycloparaffins (naphthenes) from bio-feedstocks
[23–27]. Because cycloparaffins are commonly produced through
hydrogenation of aromatics, their price may be higher than that
of aromatics [22]. However, if new production processes or feedstocks are established in the future, then it would be simpler and

cheaper to produce cycloparaffins. One promising production process for producing cycloparaffins in Indonesia is the hydrogenation
of turpentine oil obtained from pine tree (Pinus merkusii), as proposed by Hudaya et al. [28]. Although in their study they proposed
a method for producing iso-paraffins, the same method can theoretically be used to produce cycloparaffins.
Cycloparaffins and aromatics can be mixed with SBK to
decrease its freezing point since they have a lower freezing point
than that of n-paraffins with same carbon number. However, they
exhibit a very different sooting tendency. The jet fuel standard
(ASTM D1655) specifies that the maximum volume fraction of aromatics present in commercial jet fuels such as Jet A, Jet A-1, and Jet
B is 25%, whereas the fraction of cycloparaffins is not limited [17].
Soot formation in a gas turbine combustor is problematic because
it generates high radiation heat and deposits, which can damage
the combustion chamber or the turbine blade, thus reducing the
engine’s life [29,32]. In addition, the unburned soot particles emitted with the exhaust gas from a gas turbine engine are dangerous
for human health and the environment [33]. Therefore, the sooting
tendency plays an important role for evaluating a potential component to mix with SBK.
This research focuses on comparing the effects of cycloparaffins
and aromatics on the sooting tendency and the freezing point
when mixed with SBK and n-paraffin fuels. Butylcyclohexane and
butylbenzene were chosen as the surrogate components for
cycloparaffin and aromatic hydrocarbons, respectively. Because
dodecane has the same carbon number with the average SBK molecule and with jet fuel [33], it was used to represent for n-paraffins
in SBK and jet range n-paraffin fuels. Based on the results of this
work, the potential of cycloparaffins and aromatics for mixing with
SBK and n-paraffin fuels is assessed with regard to the tradeoffs
between the sooting tendency and the decrease of the freezing
point.

2. Experimental setup and procedures
2.1. Total soot volume of laminar diffusion wick-fed flame and smoke
point measurement

The experimental setup used for determining the total soot volume and measuring the smoke point is shown in Fig. 3. The total
soot volume of the laminar diffusion wick-fed flame was determined by employing a light extinction method. As shown in
Fig. 3, the burner comprised two closely fitting concentric brass
tubes (outer tube diameter = 0.8 cm, inner tube diameter = 0.5 cm)
following the methods proposed by Olson et al. [34] and Watson
et al. [35]. The outer and inner tubes belonged to the fuel tank

Decarboxylation
process

Fig. 1. Soap-derived biokerosene (SBK) production process.

Normal
paraffins


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L.H. Duong et al. / Fuel 185 (2016) 855–862

Plant oils,
animal fats

Hydrotreating
process

Isomerization &
cracking process

Normal

paraffins

(n + iso)
paraffins

Fig. 2. Hydroprocessed esters and fatty acids production process [12,30,31].

[37,38] attributed to the work of Dalzell and Sarofim [42]. The total
soot volume within the flame was calculated using Eq. (2):

Chimney

Z
Vs ¼

Burner

0

Interference
filter lens

Light source

Digital
Camera
Honeycomb

Fuel tank socket
Dry air

Valve

Flow meter

Fuel tank

Fuel
refill
& level
Wick
height
control

Fig. 3. Schematic of the experimental setup.

socket and fuel tank, respectively. By rotating the wick-height control nut, the fuel tank could shift up or down inside the fixed socket
to expose more or less of the wick, respectively, thus controlling
the flame height. ASTM specification cotton wick was used to
install to the fuel tank. A 30-cm-long, and 9-cm-outer-diameter
glass tube covered the burner as a chimney. Dry air was supplied
to the chimney at a constant flow rate of 30 L/min, or an equivalent
air velocity of 7.86 cm/s, for all measurements. Three aluminum
honeycombs were used to generate laminar flow inside the chimney. To refill the fuel and measure the fuel consumption, a 1-mminner-diameter clear glass tube was connected to the fuel tank
through a silicon pipe. If kept parallel and vertical, the level of
the fuel in the fuel tank remained the same as that in the fuel refill
tube. The fuel mass was measured with a Shimadzu UX2200H digital balance at a resolution of 0.01 g. The duration of burning was
timed with a stopwatch. The approximate flame height was determined with a ruler and then precisely determined by analyzing the
flame image recorded by a Canon VIXIA HF S21 camera. To derive
the total soot volume, a Panasonic HDC-TM750 camera with an

interference filter lens was used. This filter lens only allowed light
with 540 nm wavelength from a backlight system. The recorded
backlight image with and without the flame was used as input to
a MATLAB program to calculate the total soot volume of the flame.
The BouguerÀLambertÀBeer theory was applied to evaluate the
soot volume fraction in the Rayleigh wavelength range (particle
diameter/light wavelength (1) using Eq. (1), as the method used
in Jeon et al. [36]. The light scattering by the particles was assumed
to be negligible; this practice was commonly used by other studies
as well [36–41].

fv ¼

k ln II0
ðm À1Þ
6pLIm ðm
2 þ2Þ
2

ð1Þ

where fv is the soot volume fraction, I0 is the initial light intensity, I
is the transmitted light intensity, k is the wavelength, L is the optical
path length, and m is the optical refractive index of the soot particles. In this study, the optical refractive index of the soot particles
was m = 1.57–0.56i, in accordance with many previous studies

Hf

Z

R
0

f v ðr;zÞ 2prdrdz

ð2Þ

where Hf and R are the flame height and radius, respectively.
The smoke point of the fuel, which is defined as the maximum
height (in millimeters) of a smoke-free laminar diffusion flame of
fuel burned in a wick-fed lamp [43], was derived through the
method proposed by Olson et al. [34] and Watson et al. [35]. These
studies proposed a method of using the relationship between the
mass fuel consumption and the flame height to obtain a more accurate smoke point of the fuel, as compared to the direct visual observation presented in ASTM D1322 [43]. However, the experimental
system in this work has some slight modifications compared with
that of these studies. Instead of placing the balance under the fuel
tank to determine the fuel mass, a constant volume of fuel measured based of its mass just before filling to the fuel tank was used
for determining the duration of the burn. Theoretically, because
the temperature of the fuel tank was nearly same throughout a
measurement, the same volume of fuel has the same mass. Two
standard samples proposed by ASTM D1322 mixed with toluene
and iso-octane (2,2,4-trimethylpentane) with volume fractions of
40/60 and 10/90, respectively, were measured to compare with
the smoke point given in ASTM D1322. The results indicated that
the smoke points in this study for the 40/60 and 10/90 samples differed from that of the ASTM D1322 standard by 2.04% (15 mm versus 14.7 mm) and 0.66% (30.0 mm versus 30.2 mm), respectively.
Therefore, this method was considered reliable for measuring the
smoke point of other fuel samples.
In order to investigate the sooting tendency, several mixtures of
SBK/butylcyclohexane, and SBK/butylbenzene were used to measure on the total soot volume and the smoke point. Because the
composition of SBK consists predominantly of n-paraffins that

exhibit a carbon chain length within the jet range, some typical
n-paraffins in this range including decane, dodecane, and hexadecane were applied to measure on the total soot volume. SBK was
produced in-house from coconut oil. The composition of SBK was
analyzed by using gas chromatograph equipment named Shimadzu
2010. The weight fraction of hydrocarbon types in SBK are listed in
Table 1. The chemical compounds were purchased from SigmaAldrich Corp. and Tokyo Chemical Industry Co., Ltd. The properties
of SBK and the chemical compounds are listed in Table 2.
2.2. Freezing point measurement
The freezing points of the fuels were measured by JFE TechnoResearch Corporation in Japan using the JIS K2276 test method,
which is equivalent to ASTM D2386 or IP16 [44]. The freezing

Table 1
Composition of soap-derived biokerosene.
Hydrocarbon type

wt.%

Normal paraffins
Olefins
Aromatics
Branched paraffins

67.19
21.77
9.06
1.93


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L.H. Duong et al. / Fuel 185 (2016) 855–862

Table 2
Properties and information of soap-derived biokerosene (SBK), and hydrocarbon compounds.
Fuel

Code

Soap-derived biokerosene
Decane
Dodecane
Hexadecane
Butylcyclohexane
Butylbenzene
Toluene
2,2,4-Trimethylpentane
a
b
c
d

SBK
DEC
DOD
HEX
BCH
BBZ

Molecular formula
C7-C17

C10H22
C12H26
C16H34
C10H20
C10H14
C7H8
C8H18

CAS no.
124-18-5
112-40-3
544-76-3
1678-93-9
104-51-8
108-88-3
540-84-1

Density (kg/m3)

Purity (%)

a

F.P
d

810
730
750
774

800
860
865
692

>99.0
>99.0
>99.0
>99.0
>99.0
>99.0
>99.0

M.W

160.64
142.28
170.33
226.44
140.27
134.22
92.14
114.23

b

(°C)

0.5
À30

À9.6
18
À78
À88
À93
À107

S.P

c

(mm)

52.5
99.5
94
87.5
55.5
8.5
8
43

M.W: molecular weight.
F.P: freezing point.
S.P: smoke point.
Obtaining by estimation method.

points of several mixtures of SBK/butylcyclohexane, dodecane/
butylcyclohexane, and dodecane/butylbenzene were measured.
3. Results and discussion

3.1. Total soot volume
Fig. 4 shows that SBK has a significantly greater total soot volume compared to the n-paraffins in the range of C10–C16. This is
due to the fraction of olefins, especially, aromatics present in SBK
(Table 1). Considering the production process (Fig. 1), the product’s
composition includes unsaturated hydrocarbons such as olefins,
which are formed from the unsaturated fatty acid chains in
coconut oil. The olefins have a greater sooting tendency than the
n-paraffins with similar carbon number [34,48,49]. Besides, SBK
produces greater soot mainly due to its aromatic fraction. In decarboxylation, some fractions of the unsaturated hydrocarbon bonds
in basic-soap are converted into aromatic hydrocarbons [50,51].
Aromatics are known to have a very high soot formation
[34,48,49], and that is confirmed by the results of the present work.
The total soot volume as measured for a mixture of 90% dodecane
and 10% butylbenzene (DOD90BBZ10) by volume. Dodecane was
selected to represent the n-paraffins in SBK because it is the closest
with the average molecule of SBK. By volume, 10% butylbenzene
was mixed with dodecane since it represents the approximate fraction of the aromatics found in SBK (Table 1). As shown in Fig. 4, the

4.5

total soot volume of SBK is very close to that of DOD90BBZ10 at
several flame heights.
Fig. 4 also shows that butylcyclohexane has slightly less total
soot volume than SBK while butylbenzene has the highest total
soot volume. Therefore, blending butylcyclohexane with SBK produces less total soot volume; however, the difference is very small,
as indicated in Fig. 5. Conversely, the butylbenzene significantly
increases the total soot volume when blended with SBK, as shown
in Fig. 6. From Figs. 5 and 6, the butylbenzene clearly leads to
greater formation of soot compared to butylcyclohexane when
they are mixed with SBK. To obtain a clearer quantitative comparison regarding to the jet fuel specification, the smoke point of these

blends was measured and presented in the following section.
3.2. Smoke point
Fig. 7 shows a comparison of the effect of butylcyclohexane and
butylbenzene on the smoke point when blended with SBK. Butylcyclohexane slightly increases the smoke point because its smoke
point is a little higher compared with that of SBK (55.5 mm versus
52.5 mm), whereas, butylbenzene strongly decreases the smoke
point of these blends because it has a significantly lower smoke
point than SBK (8.5 mm versus 52.5 mm). The lower smoke point
indicates a greater tendency to form soot.
The distribution of carbon chains in aviation biofuel simulates
that of conventional jet fuel as much as possible. Thus, the carbon
chain length of the current aviation biofuels commonly lay within
the jet range (C8–C16; and average at C12 [33]). The results on the

DEC

4.5

DOD
3.5
HEX
3.0

BCH

2.5

SBK

2.0

BBZ

1.5

DOD90BBZ10

1.0
0.5

Total soot volume (10-3 mm3)

Total soot volume (10-3 mm3)

4.0

4.0

SBK

3.5

SBK75BCH25

3.0

SBK50BCH50

2.5

BCH

2.0
1.5
1.0
0.5
0.0

0.0
0

5

10 15 20 25 30 35 40 45 50 55
Flame height (mm)

Fig. 4. Total soot volume as a function of flame height of SBK, pure hydrocarbons
and mixture.

0

5

10 15 20 25 30 35 40 45 50 55
Flame height (mm)

Fig. 5. Total soot volume vs. flame height of the mixtures: SBK (100% SBK);
SBK75BCH25 (75% SBK + 25% butylcyclohexane); SBK50BCH50 (50% SBK + 50%
butylcyclohexane); BCH (100% butylcyclohexane).

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L.H. Duong et al. / Fuel 185 (2016) 855–862

Total soot volume (10-3 mm3)

4.5
4.0

SBK

3.5

SBK75BBZ25

3.0

SBK50BBZ50

2.5

BBZ

2.0
1.5
1.0
0.5
0.0
0

5

10 15 20 25 30 35 40 45 50 55
Flame height (mm)

Fig. 6. Total soot volume vs. flame height of the mixtures: SBK (100% SBK);
SBK75BBZ25 (75% SBK + 25% butylbenzene); SBK50BBZ50 (50% SBK + 50% butylbenzene); BBZ100 (100% butylbenzene).

60

Smoke point (mm)

50
SBK/BCH

40

SBK/BBZ
30

ASTM D1655 min.

20

composition. Fig. 8 indicates that both butylcyclohexane and
butylbenzene decrease the smoke point when blended with dodecane. However, butylbenzene has a much greater effect on the
smoke point than butylcyclohexane. Figs. 7 and 8 also show that
the volume fraction of butylcyclohexane blended with SBK and
dodecane could reach up to 100%, satisfying the requirement on

the smoke point of the jet fuel specified by ASTM D1655 (min.
25 mm). In contrast, the volume fraction of butylbenzene to blend
with SBK and dodecane is limited by a certain amount that is can
be estimated as shown in Fig. 9.
From Figs. 7 and 8, it becomes clear that when butylcyclohexane or butylbenzene is blended with SBK, the smoke points of
the mixtures are significantly lower than those of their mixtures
with dodecane, when using the same volume fractions. This is
because the smoke point of SBK (52.5 mm) is lower than that of
dodecane (94.0 mm). The lower smoke point of SBK is due to the
fractions of included olefins and aromatics, as shown in Table 1.
Fig. 8 also shows that the mixture of dodecane and butylbenzene
with volume fraction of 90/10 exhibits a smoke point very close
to that of SBK (52.5 mm). This observation is consistent with the
results on the total soot volume shown in Fig. 4. Based on the
results shown in Figs. 4, 7 and 8, it could conclude that the mixture
of DOD90BBZ10 is suitable as a surrogate for SBK while dodecane
can be used as a surrogate component for the jet range nparaffins to evaluate the sooting tendency.
Fig. 9 shows the correlation between the volume fraction of
butylcyclohexane or butylbenzene and the reversed smoke point
of the fuel mixtures. This correlation is consistent with the ones
proposed by Van Treuren [52] and Li and Sunderland [53] as shown
in Eq. (3).

LSP;mix ¼

10

ti

À1

ð3Þ

LSP;i

where LSP,mix, LSP,i, and ti represent the smoke point of the mixture,
the smoke point of the component i and the volume fraction of the
component i, respectively. Van Treuren proposed this correlation for

0
0

X

10 20 30 40 50 60 70 80 90 100 110
Fraction of butylcyclohexane or butylbenzene
(vol%.)

100

Fig. 7. Smoke point as a function of the butylcyclohexane and butylbenzene
content in the mixture with SBK.

Smoke Point (mm)

total soot volume in Fig. 4 shows that the differences in the total
soot volume among the n-paraffins with carbon chain length from
C10 to C16 are insignificant. Dodecane has the same carbon number with the average carbon chain length of jet fuel. Thus, it is a
good candidate for a surrogate component of biofuel for aviation
alternative fuels containing of n-paraffins, as well as n-paraffin
hydrocarbon class in the jet fuel. On the other hand, regarding

the production process of SBK, n-paraffins in SBK are expect to
have a carbon chain length shorter by one than that of the fatty
acids in coconut oil; the latter lays almost within the jet range
and predominantly at C12 [45,46] (Table 3). Therefore, the experimental results on dodecane are not only useful for studies on fuels
that consist of n-paraffins in the jet range, but also provide a good
reference for comparison with SBK to confirm its quality and

90
80
70
60
50

DOD/BCH

40

DOD/BBZ

30

ASTM D1655 min.

20
10
0
0

10 20 30 40 50 60 70 80 90 100 110
Fraction of butylcyclohexane or butylbenzene

(vol.%)

Fig. 8. Smoke point as a function of the butylcyclohexane and butylbenzene
content in the mixture with dodecane.

Table 3
Fatty acids profile of coconut oil.
Oil

Coconut oil [45]
Coconut oil [46]

Fatty acids composition (wt.%)
8:0

10:0

12:0

14:0

16:0

18:0

18:1

18:2

18:3

4.9–8.7
4.6–9.5

4.3–6.5
4.5–9.7

42.3–53.1
44–51

17.2–19.8
13–20.6

7.4–10.8
7.5–10.5

2.0–3.4
1–3.5

4.7–8.9
5–8.2

0.7–3.5
1–2.6

0–0.2
0–0.2


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L.H. Duong et al. / Fuel 185 (2016) 855–862

SBK/BCH

0.12

SBK/BBZ

0.11

DOD/BCH

-10

0.10

DOD/BBZ

-20

0.09

ASTM D1655 min.

0.08

0
0

y = 0.001x + 0.0199
R² = 0.99964

0.07
0.06

y = 0.0011x + 0.0087
R² = 0.9986

0.05
0.04

y = -1E-05x + 0.019
R² = 0.94648

0.03
0.02

y = 7E-05x + 0.0104
R² = 0.99299

0.01
0.00
0

Fraction of butylcyclohexane or butylbenzene
(vol.%)

10

0.13

10 20 30 40 50 60 70 80 90 100 110
Fraction of butylcyclohexane or butylbenzene
(vol.%)

Fig. 9. Inversed smoke point as a function of the butylcyclohexane and butylbenzene content in mixture with SBK and dodecane.

the mixture of fossil-derived liquid fuels [52], then Li and Sunderland [53] examined it for several mixtures of hydrocarbons. A
parameter that equals to a constant multiply by the inversed smoke
point was proposed as the first definition on the sooting tendency
for hydrocarbon fuels [48,54,55]. However, quantifying the sooting
tendency of hydrocarbon fuels by using this parameter remained
some shortcomings because it did not take into account the effect
of fuel molecular size on flame height. To consume a unit volume
of fuel, the fuel with higher molecular weight needs more volume
of oxygen to diffuse into the flame, thus increasing the flame height
[56]. Consequently, Threshold Sooting Index (TSI) was established
by Calcote and Manos [57] to quantify the sooting tendency for
hydrocarbon fuels to resolve this issue. Recently, Barrientos et al.
[58] proposed the use of the Oxygen Extend Sooting Index (OESI)
to extend the same concept to oxygenated fuels. Currently, TSI
and OESI are more commonly used than the inversed smoke point
for evaluating and comparing on sooting tendency of the fuels
[34,55–62]. However, there is no requirement on TSI or OESI specified by standard for jet fuel. Therefore, to find the maximum allowable volume fraction of butylcyclohexane or butylbenzene to blend
with SBK or dodecane in order to satisfy the requirement on the
smoke point of jet fuel, the correlation on inversed smoke point of
hydrocarbon mixture (Eq. (3)) was used in this study. Thereby,
the linear functions in Fig. 9 suggest that approximately 20% and
28% are the maximum allowable volumes of butylbenzene to blend

with SBK and dodecane, respectively, in order to satisfy the minimum smoke point required for jet fuel (25 mm). However, because
SBK contains some fractions of aromatics, it should be noted that
the maximum allowable volume fraction of aromatics in jet fuel is
25% according to ASTM D1655. This figure also indicates that no
limitations exist in the fraction of butylcyclohexane that hinder
its blending with SBK or dodecane to satisfy the smoke point
requirement of jet fuel.
3.3. Freezing point
The freezing point is one of the most critical properties of jet
fuel. ASTM D1655 requires that the maximum freezing point is
À47 °C for Jet A1, which is the commercial jet fuel widely used
worldwide. The n-paraffins, which have a carbon chain length

Freezing point (ºC)

[Smoke Point]-1 (mm-1)

0.14

10

20

30

40

50

60

70

80

90

100

-30
-40
-50
-60
-70

SBK/BCH
DOD/BCH
DOD/BBZ

-80
-90

ASTM D1655 max.
ASTM D1655 max. vol. frac.

-100
Fig. 10. Freezing point as a function of the butylcyclohexane and butylbenzene
content in the mixture with SBK and dodecane.

equal to the fatty acid chains in plant oils or animal fats, normally

have a much higher freezing point than À47 °C because these fatty
acids present in almost all plant oils and animal fats have carbon
chain lengths predominantly between C16 and C18 [45–47]. Therefore, to decrease the freezing point of these n-paraffins, further
processing is required. Two of the most typical such processes
are cracking and isomerization. However, these are both complicated and expensive [18–20]. Mixing SBK or n-paraffin fuels with
cycloparaffins or aromatics may also reduce the freezing point.
Fig. 10 shows that the effect on the freezing point of butylcyclohexane when blended with SBK and dodecane is almost similar. The
freezing point decreases with increasing volume fraction of butylcyclohexane in blend with SBK or dodecane. The slightly lower
freezing points of dodecane/butylcyclohexane blends are due to
the lower freezing point of dodecane (À9.6 °C) compared to SBK
(0.5 °C). This figure also indicates that butylcyclohexane decreases
the freezing point more when mixed with dodecane than butylbenzene, although the freezing point of butylcyclohexane
(À78 °C) is higher than that of butylbenzene (À88 °C). This might
due to the improved solubility of the butylcyclohexane, as compared to butylbenzene, when blended with dodecane, since the
freezing point of a liquid mixture is related to solubility [63]. Furthermore, Fig. 10 indicates that mixing butylcyclohexane with SBK
or dodecane can reduce the freezing point of the blend up to
À47 °C, thus matching the freezing point required by ASTM
D1655 for Jet A1. In contrast, because the maximum allowable volume fraction of butylbenzene in a blend is limited to 25%, which is
insufficient to achieve a freezing point of less than À47 °C when
mixed with dodecane, and definitely when blended with SBK.
4. Conclusions
The total soot volume, smoke point, and freezing point of SBK,
dodecane, and their mixtures with butylcyclohexane and
butylbenzene were measured in this study. In addition, some
n-paraffins with carbon number within the jet range, such as
decane, dodecane, and hexadecane, were also examined with
regard to their total soot volume to compare them with SBK. The
freezing point is a critical property of jet fuel and the most
challenging requirement of aviation biofuel. Blending SBK or
n-paraffins fuel with cycloparaffin and aromatic hydrocarbons,

which have low freezing points is a potential solution to reduce
the freezing point of the fuel. However, the requirement regarding


L.H. Duong et al. / Fuel 185 (2016) 855–862

the formation of soot might limit the fraction of these hydrocarbons
that can be mixed with SBK or n-paraffins. This work was done to
assess this issue, and the following conclusions were reached:

[13]
[14]

(1) Butylcyclohexane and butylbenzene produce reverse effects
on the sooting tendency and the freezing point when
blended with SBK or dodecane. Regarding the sooting tendency, butylcyclohexane produces a significantly smaller
effect compared to butylbenzene. In contrast, butylcyclohexane decreases the freezing point more than butylbenzene
although the freezing point of butylcyclohexane is higher
than that of bultylbenzene.
(2) SBK or dodecane can be blended with butylcyclohexane to
reduce the freezing point of the mixtures to meet the
requirements on both the smoke point and the freezing
point specified for jet fuel. In contrast, because of the
requirements on the smoke point and/or the maximum
allowable volume fraction of aromatics, blending SBK or
dodecane with butylbenzene is infeasible to satisfy the
freezing point.
(3) The differences in the total soot volume among n-paraffins
with carbon number range from C10 to C16 are insignificant.
Therefore, the fuel that consists of n-paraffins in this carbon

number range, especially, when dominated by C12 can use
dodecane as a surrogate for evaluating the sooting tendency.
SBK includes some fractions of olefins and aromatics, thus a
mixture of 90% dodecane and 10% butylbenzene by volume
is suitable as a surrogate of SBK to simulate the total soot
volume and the smoke point.
Considering the tradeoff between the sooting tendency and the
decrease of the freezing point, cycloparaffins are better for blending with SBK or n-paraffins fuel as compared to aromatics.

[15]

[16]
[17]

[18]
[19]

[20]
[21]
[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

Acknowledgments
We gratefully acknowledge the ASEAN University Network
Southeast Asian Engineering Education Development Network
(AUN/SEED-Net) project of the Japan International Cooperation
Agency (JICA) for financial support. OF is supported by Grant in
aid # 15K13878 for scientific research of Japan.

[30]
[31]
[32]
[33]
[34]
[35]

References
[1] Boeing. Current market outlook 2015–2034. Boeing commercial airplanes,
market analysis, P.O. Box 3707, MC 21–28, Seattle, WA 98124–2207; 2015.
[2] Airbus. Global market forecast 2014–2034. Airbus S.A.S 31707 Blagnac Celdex;
2014.
[3] International Air Transport Association. IATA economic briefing: airline fuel
and labour cost share; February 2010.
[4] Intergovernmental Panel on Climate Change (IPCC) 1999. Aviation and the
global atmosphere; 2015. < />src=/Climate/ipcc/aviation/index.html> [accessed 15.12.02].
[5] European Directive 2008/101/CE on Aviation Gas Emission.
[6] Pope J, Owen AD. Emission trading schemes: potential revenue effects,

compliance costs and overall tax policy issues. Energy Policy 2009;37
(11):595–603.
[7] Deane P, Shea RO, Gallachoir BO. Biofuels for aviation, rapid response energy
brief. Insight; April 2015.
[8] International Air Transport Association. IATA 2014 Report on alternative fuels.
Montreal–Geneva; December 2014.
[9] ASTM D7566. Standard specification for aviation turbine fuel containing
synthesized hydrocarbons. American Society for Testing and Materials; 2016.
[10] Rogelio SB, Fernando TZ, Felipe JHL. Hydroconversion of triglycerides into
green liquid fuels. In: Karame Iyad, editor. Hydrogenation. Mexico: InTech;
2012. p. 187–216.
[11] Klingshirn CD, DeWitt M, Striebich R, Anneken D, Shafer M. Hydroprocessed
renewable jet fuel evaluation, performance, and emissions in a t63 turbine
engine. J Eng Gas Turbines Power 2012;134:051506-1–6-8.
[12] Rahmes TF, Kinder JD, Henry TM, Crenfeldt G, LeDuc GF, Zombanakis GP, et al.
Sustainable bio-derived synthetic paraffinic kerosene (Bio-SPK) jet fuel flights
and engine tests program results. In: 9th AIAA aviation technology,

[36]

[37]

[38]
[39]

[40]
[41]
[42]
[43]
[44]

[45]

[46]

861

integration, and operations conference. Hilton Head, South Carolina 21–23
September 2009.
Blakey S, Rye L, Wilson CW. Aviation gas turbine alternative fuels: a review.
Proc Combust Inst 2011;33:2863–85.
Speth RL, Rojo C, Malina R, Barrett SRH. Black carbon emissions reductions
from combustion of alternative jet fuels. Atmos Environ 2015;105:37–42.
Badami M, Nuccio P, Pastrone D, Signoretto A. Performance of a small-scale
turbojet engine fed with traditional and alternative fuels. Energy Convers
Manage 2014;82:219–28.
Aviation fuels technical review. ChevronTexaco Corporation; 2005.
The Coordinating Research Council, Inc., Handbook of aviation fuel properties.
In: Society of Automotive Engineers Publications Department 400
Commonwealth Drive Warrendale. Pennsylvania 15096. 3th ed.; 2004, p. 1–6.
Gary JH, Handwerk GE. Petroleum refining–technology and economics. 4th
ed. New York: Marcel Dekker; 2001. p. 93.
Wang T, Li K, Liu Q, Zhang Q, Qiu S, Long J, et al. Aviation fuel synthesis by
catalytic conversion of biomass hydrolysate in aqueous phase. Appl Energy
2014;136:775–80.
Fu J, Yang C, Wu J, Zhuang J, Hou Zh, Lu X. Direct production of aviation fuels
from microalgae lipids in water. Fuel 2015;139:678–83.
Kallio P, Pasztor A, Akhtar MK, Jones PR. Renewable jet fuel. Curr Opin
Biotechnol 2014;26:50–5.
Zhang Y, Bi P, Wang J, Jiang P, Wu X, Xue H, et al. Production of jet and diesel

biofuels from renewable lignocellulosic biomass. Appl Energy 2015;150:
128–37.
Wang J, Bi P, Zhang Y, Xue H, Jiang P, Wu X, et al. Preparation of jet fuel range
hydrocarbons by catalytic transformation of bio-oil derived from fast pyrolysis
of straw stalk. Energy 2015;86:488–99.
Wang T, Qiu S, Weng J, Chen L, Liu Q, Long J, et al. Liquid fuel production by
aqueous phase catalytic transformation of biomass for aviation. Appl Energy
2015;160:329–35.
Bi P, Wang J, Zhang Y, Jiang P, Wu X, Liu J, et al. From lignin to cycloparaffins
and aromatics: directional systhesis of jet and diesel fuel range biofuels using
biomass. Bioresour Technol 2015;183:10–7.
Carlson TR, Tompsett GA, Conner WC, George. Aromatic production from
catalytic fast pyrolysis of biomass-derived feedstocks. Top Catal
2009;52:241–52.
Olcay H, Subrahmanyam AV, Xing R, Lajoie J, Dumesic JA, Huber GW.
Production of renewable petroleum refinery diesel and jet fuel feedstocks
from hemicellulose sugar streams. Energy Environ Sci 2013;6:205–16.
Hudaya T, Rionardi A, Soerawidjaja TH. Electrochemical hydrogenation of
terpene hydrocarbons. In: International seminar on biorenewable resources
utilization for energy and chemicals. Bandung, Indonesia 10–11 October 2013.
Fiswell NJ. The influence of fuel composition on smoke emission from gasturbine-type combustors: effect of combustor design and operating
conditions. Combust Sci Technol 1979;19:119–27.
Speight JG. The chemistry and technology of petroleum. 4th ed. New York: CRC
Press; 2006.
Altman R. Aviation alternative fuels, characterizing the options. In: Aviation
and alternative fuels (ICAO). Montreal, Canada: ICAO; 2009.
Wey C, Powell EA, Jagoda JI. The effect of temperature on the sooting behavior
of laminar diffusion flames. Combust Sci Technol 1984;41:173–90.
Lefebvre AH, Ballal DR. Gas turbine combustion. 3th ed. CRC Press; 2010. p. 39.
Olson DB, Pickens JC, Gill RJ. The effects of molecular structure on soot

formation II. Diffusion flames. Combust Flame 1985;62:43–60.
Watson RJ, Botero ML, Ness CJ, Morgan NM, Kraft M. An improved
methodology for determining threshold sooting indices from smoke point
lamps. Fuel 2013;111:120–30.
Jeon BH, Fujita O, Nakamura Y, Ito H. Effect of co-axial flow velocity on soot
formation in a laminar jet diffusion flame under microgravity. J Therm Sci
Technol 2007;2(2):281–90.
Saffaripour M, Veshkini A, Kholghy M, Thomson MJ. Experimental
investigation and detailed modeling of soot aggregate formation and size
distribution in laminar coflow diffusion flames of Jet A-1, a synthetic kerosene,
and n-decane. Combust Flame 2014;161:848–63.
Merchan-Merchan W, McCollam S, Pugliese JFC. Soot formation in diffusion
oxygen-enhanced biodiesel flames. Fuel 2015;156:129–41.
Feng Q, Jalali A, Fincham AM, Wang JL, Tsotsis TT, Egolfopoulos FN. Soot
formation in flames of model biodiesel fuels. Combust Flame 2012;159
(5):1876–93.
Snelling DR, Thomson KA, Smallwood GJ, Gulder OL. Two-dimensional imaging
of soot volume fraction in laminar diffusion flames. Appl Opt 1999;38:2478–85.
Greenberg PS, Ku JC. Soot volume fraction imaging. Appl Opt
1997;36:5514–22.
Dalzell WH, Sarofim AF. Optical constants of soot and their application to heatflux calculations. J Heat Transfer 1969;91(4):91–100.
ASTM D1322. Standard test method for smoke point of kerosine and jet
fuel. American Society for Testing and Materials; 2012.
Nadkarni RAK. Guide to ASTM test methods for the analysis of petroleum
products and lubricants. West Conshohocken, PA: American Society for Testing
and Materials; 2000. p. 152.
Hoekman SK, Broch A, Robbins C, Ceniceros E, Natarajan M. Review of biodiesel
composition, properties, and specifications. Renew Sustain Energy Rev
2012;16:143–69.
Knothe G, Gerpen JV, Krahl J. The biodiesel handbook. Cham-paign,

Illinois: AOCS Press; 2005.


862

L.H. Duong et al. / Fuel 185 (2016) 855–862

[47] Speight JG. In: Julian Hunt FRS, editor. The biofuels handbook. RSC energy
series, vol. 5. Science Park, Milton Road, Cambridge CB4 0WF, UK: The Royal
Society of Chemistry, Thomas Graham House; 2011. p. 92.
[48] Clarke AE, Hunter TG, Garner FH. Tendency to smoke of organic substances on
burning: part I. Ind Eng Chem 1946;32:627–42.
[49] Hunt RA. Relation of smoke point to molecular structure. Ind Eng Chem
1953;45(3):602–6.
[50] Lappi H, Alen R, Anal J. Production of vegetable oil-based biofuels:
thermochemical behavior of fatty acid sodium salts during pyrolysis. J Anal
Appl Pyrol 2009;86:274–80.
[51] Zhenyi C, Xing J, Shuyuan L, Li L. Thermodynamics calculation of the pyrolysis
of vegetable oils. Energy Sources 2004;26:849–56.
[52] Van Treuren KW. Sooting characteristics of liquid pool diffusion flames M.S.
thesis. USA: Mechanical and Aerospace Engineering, Princeton University;
1978.
[53] Li L, Sunderland PB. Smoke points of fuel–fuel and fuel–inert mixtures. Fire Saf
J 2013;61:226–31.
[54] Kewley J, Jackson JS. The burning of mineral oils in wick-fed lamps. J Inst Petrol
Technol 1927;13:364–82.
[55] Minchin ST. Luminous stationary flames: the quantitative relationship
between flame dimensions at sooting point and chemical composition with

[56]

[57]
[58]

[59]
[60]

[61]

[62]
[63]

special reference to petroleum hydrocarbons. J Inst Petrol Technol
1931;17:102–20.
Mensch A, Santoro RJ, Litzinger TA, Lee SY. Sooting characteristics of surrogates
for jet fuels. Combust Flame 2010;157:1097–105.
Calcote HF, Manos DM. Effect of molecular structure on incipient soot
formation. Combust Flame 1983;49:289–304.
Barrientos EJ, Lapuerta M, Boehman AL. Group additivity in soot formation for
the example of C-5 oxygenated hydrocarbon fuels. Combust Flame
2013;160:1484–98.
Llamas A, Lapuerta M, Al-Lal A, Canoira L. Oxygen extended sooting index of
fame blends with aviation kerosene. Energy Fuels 2013;27(11):6815–22.
Jiao Q, Anderson JE, Wallington TJ, Kurtz EM. Smoke point measurements of
diesel-range hydrocarbon–oxygenate blends using a novel approach for fuel
blend selection. Energy Fuels 2015;29:7641–9.
Barrientos EJ, Anderson JE, Maricq MM, Boehman AL. Particulate matter
indices using fuel smoke point for vehicle emissions with gasoline, ethanol
blends, and butanol blends. Combust Flame 2016;167:308–19.
Gómez A, Soriano JA, Armas O. Evaluation of sooting tendency of different
oxygenated and paraffinic fuels blended with diesel fuel. Fuel 2016;184:536–43.

Affens WA, Hall JM, Holt S, Hazlett RN. Effect of composition on freezing points
of model hydrocarbon fuels. Fuel 1984;64:543–7.