Fuel 89 (2010) 3807–3813

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

Limitations of the use of cetane index for alternative compression ignition

engine fuels
Noel Bezaire, Kapila Wadumesthrige, K.Y. Simon Ng, Steven O. Salley *
Department of Chemical Engineering, Wayne State University, 5050 Anthony Wayne Drive, Detroit, MI 48202, USA

a r t i c l e i n f o a b s t r a c t

Article history: The cetane number of a fuel is an important factor in determining the quality of ignition in compression
Received 15 October 2009 ignition (CI) engines. The significance of accurate measurement of cetane number has become even
Received in revised form 28 May 2010 greater since the use of alternative fuels and modern CI engines. In this work, the comparison of different
Accepted 14 July 2010
methods of cetane value measurement for fuels with different chemical composition such as ultra low
Available online 24 July 2010
sulfur diesel (ULSD), synthetic jet fuel (S-8) and military grade jet fuel (JP-8), trace amounts of additives
and biodiesel blends under different conditions is reported. The cetane index was calculated by ASTM
Keywords:
D4737 and ASTM D976 and the derived cetane number (DCN) was measured using an Ignition Quality
Cetane number
Cetane index
Tester (IQT) as a basis of comparison with the cetane index. The best agreement among three methods
Ignition quality was observed for ULSD, while S-8 showed the largest discrepancy. The cetane indices for S-8 were
Alternative fuels 70.2 and 67.3 calculated using D4737 and D976 respectively, while the DCN was 52.8. The addition of
CI engines biodiesel to ultra low sulfur diesel (ULSD) fuel alters the chemical properties of the fuel. The derived
cetane number reflected the increase in ignition quality with the addition of biodiesel while calculations
for cetane index did not. The cetane indices for a commercial B20 were 45.30 and 46.70 while the DCN
showed a significantly higher value of 48.50. Blending 5% oxidized biodiesel with ULSD caused an 8%
increase in the derived cetane number of the blend. The cetane index of the 5% biodiesel was not signif-
icantly affected by oxidation. The effects of fuel additives on cetane measurements were reflected in the
DCN measurements, but not with cetane indices.
Published by Elsevier Ltd.

1. Introduction duce the smoke during start up. Higher cetane numbers will also
increase fuel economy, reduce exhaust emissions, decrease the
The cetane number is a measure of the ignition quality or the knocking and noise of the engine, and improve the overall durabil-
auto ignition tendency of a fuel under the compression ignition ity of the engine [3–7]. The problematic long-term supplies of oil
process [1–7]. Ignition quality is quantified by measuring the igni- and, also the regulatory actions taken by the Environmental Pro-
tion delay, which is the time period between the injection of the tection Agency (EPA) and the Energy Policy Act (EPAct) have in-
fuel into the combustion chamber and the start of combustion creased the use of alternative fuel percentages in CI engines. Also
[1–7]. Fuels with shorter ignition delay (high cetane number) start the use of alternative fuels such as JP-8 and synthetic aviation fuels
to ignite shortly after injection into the cylinder, thereby having in the nontactical military ground fleet under the directive of the
enough time for complete combustion of fuel during the power Single Fuel Forward (SFF) policy [8,9] is under active evaluation.
stroke. Fuels with a lower cetane number can be accumulated be- With these factors and with modern CI engine technologies, the
fore the start of combustion. This leads to a sudden pressure rise cetane number has become a more important parameter for fuel
followed by pressure pulses and subsequent vibrations causing combustion now than a decade ago.
diesel knock, which leads to poor thermal efficiency, excessive The cetane number has been included as a fuel quality specifi-
noise and reduced life of engine components. Lower cetane num- cation in the petroleum diesel standard, with a minimum of 40
bers result in poor combustion characteristics and lead to excessive in the American Society for Testing and Materials (ASTM) D975-
emissions of smoke and particulates. Improving the cetane number 09a [10] as well as biodiesel standards, with a minimum of 47 pre-
in diesel fuel has several beneficial effects on the engine. Higher ce- scribed for neat biodiesel in ASTM D6751-09 [11], and a minimum
tane numbers improve cold starting of the engine and will also re- of 51 in some European countries (e.g., German standard E DIN
51606). However, engine manufacturers specify their own cetane
* Corresponding author. Tel.: +1 313 5775216; fax: +1 313 5773810. requirements depending on the engine design and operating con-
E-mail address: ssalley@wayne.edu (S.O. Salley). dition. Depending on the molecular composition of the fuel, a wide

0016-2361/$ - see front matter Published by Elsevier Ltd.

doi:10.1016/j.fuel.2010.07.013
3808 N. Bezaire et al. / Fuel 89 (2010) 3807–3813

range of cetane numbers ranging from 35 to 55 is observed. Some Jet fuels [27–29] and biodiesel blends [30,31]. In some reports,
special compounds, called cetane improvers, are frequently added the cetane index calculated using ASTM D976 is reported as cetane
to diesel fuel to increase the cetane number. number. There are discrepancies, however, among the cetane val-
The CN of a diesel fuel is defined as the percentage by volume of ues calculated using the different methods. Cetane number calcu-
normal hexadecane (cetane, C16H34), in a blend with 2,2,4,4,6,8,8- lated by ignition delay heavily depends on the chemical
heptamethylnonane (iso-cetane), which matches the ignition qual- properties of the fuel. Chemical compounds even at trace amounts,
ity (ignition delay of 2.407 ms) of the diesel fuel being rated under such as cetane improvers present in fuel and biodiesel components
the specified test conditions of ASTM D613-08 [12] test method. By and oxidative products in biodiesel which affects the initiation of
definition and somewhat arbitrarily, normal cetane has been as- combustion may not affect the physical properties such as boiling
signed a CN of 100 whereas iso-cetane has a CN of 15. This implies temperature and density. Cetane index, however, is influenced by
that CN = % (n-cetane) + 0.15(% iso-cetane). physical properties. As a result, cetane index may not be a suitable
The ASTM D613 method involves running the fuel in a special, method for the approximation of the cetane number for biodiesel
expensive, single cylinder diesel engine called a Cooperative Fuel blends. It is known that the oxidation of biodiesel blends changes
Research (CFR) engine with a continuously variable compression the chemical properties of the fuel, however it is assumed that
ratio under a fixed set of conditions. This test method suffers from the physical properties of the fuel would not change significantly
many disadvantages, some of which include a relatively large fuel enough to accurately predict a cetane number.
sample volume requirement, significant time consumption, and a The objective of this study is to analyze the differences between
high reproducibility error. derived cetane number as measured by the IQT™ with the cetane
Therefore, there have been many attempts to develop alternate index by ASTM D4737 and ASTM D976 for fuels with different
tests to replace the ASTM D613 method. These include devising chemical compositions and fuels with trace amounts of additives.
better engine tests and developing correlative models to predict The study also investigates how the conditions of biodiesel blends
CN from bulk properties of the fuel that may be measured more affect cetane measurements. The data presented here will help
quickly and reliably. A common method for measuring cetane both the academic and industrial communities to identify the
number is ASTM D-6890-08 [13]. ASTM D6890 measures the igni- proper use of cetane measurement techniques appropriate for
tion delay of the fuel with an Ignition Quality Tester (IQT). The igni- the type of fuel. With the increasing demand of alternative fuels
tion delay is used to calculate the derived cetane number (DCN) such as synthetic F-T fuels and biodiesels and modern high speed
and the results are accurate with a repeatability of 0.7 for cetane CI engines, the accurate measurement of ignition delay (cetane
numbers between 33 and 60 [13,14]. The test is feasible because number) is important.
of the small sample volume and relatively lower cost. It has been
shown that the DCN corresponds well with the cetane number
2. Materials and methods
measured by engine ASTM D613 [14]. The ASTM D2 committee ap-
proved ASTM D6890 for inclusion within the US Diesel Specifica-
2.1. Materials
tion ASTM D975 and biodiesel specification (B100) ASTM D6751
as an alternative to the established ASTM D613 test method, which
2.1.1. Fuels
for the short term will remain the referee test procedure. There are
Biodiesel produced from soybean oil (SBO), was obtained from
numerous reports available on the use of IQT™ for the measure-
NextDiesel, (Adrian, Michigan). Certification #2 ultra low sulfur
ment of DCN [6,7,15–20]. Some of these reports use IQT™ as a reli-
diesel (ULSD) was obtained from Haltermann Products (Channel-
able experimental tool to compare the predicted cetane numbers
view, Texas). A sample of synthetic aviation fuel (S-8) produced
using different mathematical models [19,20].
by Syntroleum Corporation, (Tulsa, Oklahoma) and military grade
Cetane index may also be used to estimate the cetane number
jet fuel (JP-8) were provided by National Automotive Center, US
of a fuel. ASTM D4737 [21] uses a four variable equation for esti-
Army, Warren, Michigan. The commercial ULSD and B20 were pur-
mation and is based on the bulk physical properties of the fuel such
chased from RKA Petroleum Corporation (Romulus, MI). A sample
as density and boiling temperature. ASTM D4737 was originally re-
of cold flow additive, Cold Flo 6300 RK (Midcontinent Chemical
leased in 1996 as ASTM D 4737-96a, and the active current version
Company, Overland Park, KS) (CFA) was kindly provided by RKA
is ASTM D 4737-04. ASTM D4737 is only to be used when ASTM
Petroleum Corporation.
D613 is not available. The estimation by this method is not to be
used when cetane improvers are added and is only valid when
the boiling temperature at 90% recovery is less than 382 °C. ASTM 2.1.2. Distillation of biodiesel
D976-06 [22] is a supplementary estimation for cetane index that Five hundred millilitres of SBO biodiesel were distilled under
is based upon American Petroleum Institute (API) gravity and reduced pressure (3  103 Torr) at about 130–150 °C. The distilla-
boiling temperatures in the middle range. It is stated in ASTM tion was performed to remove natural antioxidants present in the
D976-06, that this test method is one tool available for estimating biodiesel. Analysis of the distillates using a Perkin–Elmer (Shelton,
Calculated Cetane Index where a test engine is not available for CT) Clarus 500 gas chromatograph equipped with a flame ioniza-
determining Cetane number. It may be employed for approximat- tion detector (GC-FID) indicated that they contained only FAMEs
ing cetane number where the quantity of sample is too small for an [17]. Once distilled, they were stored at 4 °C. Portion of this dis-
engine rating. In cases where the cetane number of a fuel has been tilled biodiesel was kept in a glass bottle in ambient conditions
initially established, the index is useful as a cetane number check for 1 year. This oxidation resulted in a derived cetane number of
on subsequent samples of that fuel, provided its source and mode 120.
of manufacture remain unchanged [22], indicating that this meth-
od is suitable as a cross check of cetane number of fuels with iden- 2.1.3. Biodiesel blend preparation
tical fuel compositions. The blends of regular, distilled and oxidized biodiesel in ULSD
Because of the simplicity and availability of the instruments to on a 1%, 2%, 5%, 10%, 15% and 20% volume basis were prepared
measure bulk physical properties, the above two cetane indices are and stored in dark glass bottles at room temperature. A blend of
widely used to represent ignition quality both in industrial and 20% biodiesel with 80% ULSD, by volume, is termed: ‘‘B20”. Both
academic environments, regardless of the types of fuels, such as cetane indices and DCN measurements for given blends were car-
petroleum diesel [23,24], Synthetic F-T fuels [25–27], petroleum ried out within the same day.
 N. Bezaire et al. / Fuel 89 (2010) 3807–3813 3809

2.2. Cetane value measurement methods ASTM D976-04 was a second method used to calculate the ce-
tane index. This method utilized API gravity and the mid-boiling
2.2.1. Ignition delay and DCN measurements temperature as shown in Eq. (2):
The DCN was determined with the IQT™ (Advanced Engineer-
ing Technology, Inc., Ottawa, Canada). All samples were filtered CCI ¼ 420:34 þ 0:016G2 þ 0:192G log M þ 65:01ðlog MÞ2
prior to IQT™ testing using a threaded syringe fitted with a dispos-  0:0001809M 2 ð2Þ
able 5 lm hydrophobic fluoropore (PTFE) filter (MillexÒ-LS, Milli-
pore, Bedford, MA). The IQT™ simulates the combustion in a where CCI = calculated cetane index, G = API gravity, M = Mid-boil-
compression ignition engine and measures the delay time between ing temperature, °F.
injection and ignition of fuel injected into a constant volume com-
bustion chamber which contains compressed air at about 550 °C. A
complete combustion sequence comprised 15 preliminary cycles 3. Results and discussion
to provide equilibrium operating conditions and 32 further test cy-
cles. The ignition delays for the last 32 cycles were averaged to pro- 3.1. Cetane values of commercial fuels
duce the ID result. Each test consumes about 10 mL of sample
volume. The IQT™ system software has its own list of test methods The cetane indices of commercial ULSD, B20 (20% biodiesel in
definitions (including DCN correlation equations) that is used ULSD), Synthetic Paraffinic Kerosene, (S-8) and military grade jet
when analyzing its test results. For fuels with ignition delays be- fuel (JP-8) were calculated using the measured boiling tempera-
tween 3.3 and 6.4 ms the following equation is used as given by tures and densities. Although, the cetane number is not an impor-
ASTM 6890 (7b): tant parameter for turbine engines, the US military implemented
the Single Fuel Forward [8,9] policy, which allows the use of avia-
DCNIQT ¼ 4:46 þ ð186:6=IDÞ tion fuels in CI engines for military ground vehicles, power gener-
ators and associated equipment, thereby giving the significance of
Outside this range the following correlation equation is used. cetane measurements for aviation fuels. The distillation curves for
all four fuels are presented in Fig. 1. The initial boiling point (IBP)
DCNIQT ¼ 83:99  ðID  1:512Þ0:658 þ 3:547 and the boiling temperatures at 10% (T10), 50% (T50), and 90% (T90)
recovery points together with API gravities and specific gravities at
The standard deviation of the 32 combustion events was also 15 °C are given in Table 1. These physical parameters were used to
calculated. The IQT™ was calibrated with heptane as the primary calculate cetane indices according to the ASTM D4737 and ASTM
reference fuel. All tests were repeated three times and the average D976 methods, and are presented in Table 1 along with the derived
values are presented. The term derived is used to indicate the fact cetane numbers as measured using ASTM D6870. As shown in
that the CN was not measured in the actual CFR engine. However in Fig. 1, the distillation curves for each fuel varied significantly.
terms of actual numbers, the IQT DCN is the same as what would The composition of ULSD (based on the certificate of analysis) is
have been measured if the fuel had been run through the actual aromatics 27.5%, saturated hydrocarbons 70.8%, and olefins 1.7%
CFR cetane engine. by volume; while S-8 contains 100% C7–C18 alkanes. S-8, with
lower molecular weight hydrocarbons, shows lower distillation
2.2.2. Calculation of cetane indices temperatures at recovery points below about 75% recovery. B20
The API gravity of each fuel was measured using ASTM D1298 with 20% high boiling point fatty acid methyl esters (FAME) has
[32]. The Petroleum Measurement Tables in Guide D1250 [33] the highest boiling temperatures at any given recovery point.
were used to convert the API reading into specific gravity (SG) at As indicated in Eqs. (1) and (2), both methods for cetane index
15 °C. A hydrometer (model number 254393) manufactured by are based upon measurements of physical parameters such as boil-
H-B Instrument Co. (Collegeville, PA) with an accuracy of 0.1 was ing point, API, and density. S-8 has the lowest boiling temperatures
used to measure API gravity. These measurements were taken at 0%, 10%, and 50% recovery levels as indicated in Table 1. The dis-
three times each. crepancy among the cetane numbers measured using different
The ISL AD86 5G2 automated distillation analyzer (PAC, Pasa- methods as shown in Fig. 2 is highest for S-8. Interestingly, there
dena, TX) was operated using ASTM D86 [34] to construct the boil- is about a 4% difference in cetane index values between ASTM
ing curves of all of the fuels, with 0.3 °C temperature and 0.1 mL D47437 and ASTM D976 for S-8, which both uses bulk physical fuel
volume accuracies. The boiling curves were generated by plotting
temperature (°C) as a function of percent recovery. Using the den-
sity measurements and boiling point curves, ASTM D 4737-04 was
used to calculate the cetane index as shown in Eq. (1):

CCI ¼ 45:2 þ ð0:0892ÞðT 10N Þ þ ½0:131 þ ð0:901ÞðBÞ½T 50N 

þ ½0:0523  ð0:420ÞðBÞ½T 90N  þ ½0:00049½ðT 10N Þ2
 ðT 90N Þ2 ð107ÞðBÞ þ ð60ÞðBÞ2 ð1Þ

where CCI = calculated Cetane Index by four variable equation, D =

Density at 15 °C, g/mL determined by Test Method D1298,
DN = D0.85, B = [e(3.5)(DN)]1, T10 = 10% recovery temperature,
°C, determined by Test Method D 86 and corrected to standard
barometric pressure, T10N = T10 215, T50 = 50% recovery tempera-
ture, °C, determined by Test Method D 86 and corrected to standard
barometric pressure, T50N = T50 260, T90 = 90% recovery tempera-
ture, °C, determined by Test Method D 86 and corrected to standard
barometric pressure, T90N = T90310. Fig. 1. Distillation curves of commercial ULSD, B20, JP8 and S-8.
3810 N. Bezaire et al. / Fuel 89 (2010) 3807–3813

Table 1
Distillation (boiling) temperatures (°C) at different recovery levels, calculated cetane
indices and DCN of commercial fuels.

Property B 20 ULSD JP-8 S-8

IBP 174.28 173.00 167.78 152.78
T10 221.94 212.56 185.56 171.11
T50 278.56 259.61 210.00 202.22
T90 323.44 304.00 241.11 248.33
API 33.20 36.00 44.60 55.70
SG(15 °C) 0.86 0.85 0.80 0.76
CI ASTM D4737 45.30 45.00 48.50 70.20
CI ASTM D976 46.70 45.90 47.30 67.30
DCN ASTM D6890 48.5 ± 0.2 43.5 ± 0.4 44.8 ± 0.31 52.8 ± 0.79

Fig. 3. Distillation curve for 1%, 5%, 10%, 15%, and 20% regular biodiesel in ULSD.

Table 2 displays the distillation temperature for fuel with differ-

ent regular biodiesel blends at various points of recovery. The table
also displays values for API gravity, specific gravity at 15 °C (SG),
cetane index (CI) for ASTM D4737 and D976 as well as the derived
cetane number (DCN). The comparison of cetane index to derived
cetane number is illustrated in Fig. 4.
As previously stated cetane index is dependent upon the API
gravity and boiling curve of the fuel. Table 2 shows a difference
in API gravity as much as 1.6 from 0% to 20% of biodiesel concen-
tration. Fig. 3 shows a clear separation of the boiling curves for bio-
diesel concentrations at 5% and above. This corresponds to an
apparent increase in cetane index from 5% to 20% biodiesel as
Fig. 2. Comparison of calculated cetane indices and DCN measured using IQT of
shown in Fig. 4.
ULSD, B20, S-8 and JP-8.
The certification #2 ULSD exhibited a DCN value of 41.8 (Table
2), which was in agreement with prior studies [7]. Biodiesel
properties to calculate cetane index. The DCN of S-8 obtained using improves combustion in compression ignition engines and, as
the experimentally measured ignition delay was 52.8, which is 12 illustrated in Fig. 4, the derived cetane number increases with an
units lower than the CI by the D47437 method. The DCNs of all increase in the concentration of biodiesel. Although cetane index
fuels except B20 are lower than the calculated cetane indices. is only slightly affected by biodiesel concentrations below 5%, the
The DCN of B20 is higher than the calculated cetane indices. The derived cetane number increases across the entire range of concen-
five units higher DCN of ULSD compared to B20 can be attributed trations tested. This is because the addition of biodiesel alters the
to the nature of biodiesel, however these effects were not repre- chemical properties especially related to combustion [18,35,36]
sented in methods of calculating cetane indices. The two calculated of the fuel and the derived cetane number is sensitive to such
cetane indices for JP-8 are in good agreement but about four units changes. The derived cetane number also indicates a shorter igni-
higher than the corresponding DCN value. These results clearly tion delay than cetane index. If the increase in concentration
show the discrepancies in measurement of cetane values using affects the combustion of the fuel more than the physical proper-
different methods. ties, this would lead to the discrepancies found between derived
cetane number and cetane index.
3.2. Cetane number of biodiesel blends
3.2.2. Distilled biodiesel
3.2.1. Regular biodiesel As stated earlier, distillation removes volatile oxidative prod-
As mentioned above, the DCN of B20 is higher than the calcu- ucts in biodiesel. About 2 v% of oxidative and other minor products
lated CI. Since the use of biodiesel in diesel engines has increased were removed. A boiling curve for 1%, 5%, 10%, 15%, and 20% dis-
tremendously during recent years, it is important to study the tilled biodiesel was constructed and is illustrated in Fig. 5. The data
cetane measurements of biodiesel blends. It has been reported that in Fig. 5 does not vary significantly from the data shown in Fig. 3.
the combustion characteristics of biodiesel blends depends on the The boiling temperatures at each recovery point are relatively the
conditions such as, storage time and oxidation status of the biodie- same even after the biodiesel has been distilled.
sel [35]. This section compares the measurements of cetane values Table 3 displays the distillation temperature for fuel with differ-
of ULSD as a function of percentage of biodiesel (regular). Boiling ent distilled biodiesel blends at various points of recovery. The ta-
curves for 1%, 5%, 10%, 15%, and 20% biodiesel were constructed ble also displays values for API, specific gravity at 15 °C (SG), cetane
and is illustrated in Fig. 3. The figure shows all of the curves in index (CI) for ASTM D4737 and D976 as well as the measured de-
close proximity from 0% to 20% recovery and then they start to di- rived cetane number (DCN). When comparing the values in Table 3
verge. The curves then start to converge again from 90% to 100% to the values in Table 2, it can be seen that there is not a significant
recovery. The fuel with the highest biodiesel concentration also change in the numbers. A comparison of cetane index to derived
has the most elevated boiling curve. The fuels with larger concen- cetane number is illustrated in Fig. 6.
trations of biodiesel (fatty acid methyl esters) require more heat to The trend for cetane index in Fig. 6 is highly comparable to the
boil. trend presented in Fig. 4. In both cases there is an increase from a
 N. Bezaire et al. / Fuel 89 (2010) 3807–3813 3811

Table 2
Distillation temperatures (°C), API gravity, specific gravity (SG), cetane index, and derived cetane number for 1%, 5%, 10%, 15%, and 20% blends of regular biodiesel (BD) in ULSD.

Property #2 ULSD 1% BP 5% BD 10% BD 15% BD 20% BD

IBP 185.22 187.33 186.33 186.78 188.94 189.67
T10 202.28 202.44 203.50 204.61 205.50 208.44
T50 246.00 248.56 251.06 259.39 264.50 271.72
T90 302.11 305.67 309.67 321.44 323.56 328.00
API 36.20 36.10 35.70 35.10 35.00 34.60
SG (15 °C) 0.8438 0.8443 0.8463 0.8493 0.8499 0.8519
CI D4737 44.1 44.4 44.4 45.0 45.7 46.2
CI D976 44.2 44.7 44.7 45.8 46.8 47.6
DCN D6890 41.84 ± 0.12 44.1 ± 0.19 45.86 ± 0.26 46.92 ± 0.35 47.87 ± 0.62 48.56 ± 0.82

Fig. 6. Comparison of cetane index by ASTM D4737 and ASTM D976 to derived
Fig. 4. Comparison of cetane index by ASTM D4737 and ASTM D976 to derived cetane number for distilled biodiesel in concentrations of 1%, 5%, 10%, 15%, and 20%
cetane number for biodiesel in concentrations of 1%, 5%, 10%, 15%, and 20% in ULSD. in ULSD.

cetane index of about 44.5 to a range between 46 and 48. The in-
crease does not occur in concentrations below 5% biodiesel. As
shown in previous data, the cetane index remains relatively unaf-
fected by the chemical properties of the fuel. It can be seen that the
distillation of the biodiesel had almost no effect on the calculated
cetane index.
The derived cetane numbers of distilled biodiesel show that the
numbers lower than the regular biodiesel. The derived cetane
number for 5% distilled biodiesel was about 43.94 compared to
45.86 for the 5% regular biodiesel blend. By distilling the biodiesel
before it was blended, the volatile components which act as cetane
improvers were removed. Thus, when the blended fuel was in-
jected into the engine, the ignition delay increased which resulted
in a lower cetane number. However, the cetane indices are same
for both regular and distilled biodiesel blends with ULSD.

3.2.3. Oxidized biodiesel

A boiling curve for 1%, 2%, and 5% aged biodiesel in ULSD was
Fig. 5. Distillation curve for 1%, 5%, 10%, 15%, and 20% distilled biodiesel in ULSD. constructed and is illustrated in Fig. 7. As the figure shows, the

Table 3
Distillation temperatures (°C), API gravity, density, cetane index, and derived cetane number for 1%, 5%, 10%, 15%, and 20% blends of distilled biodiesel (DBD) in ULSD.

Property #2 ULSD 1% DBD 5% DBD 10% DBD 15% DBD 20% DBD
IBP 185.22 187.39 188.44 186.67 189.83 190.00
T10 202.28 202.56 203.72 205.11 206.67 208.72
T50 246.00 248.06 252.39 257.28 264.44 271.94
T90 302.11 303.78 311.17 317.72 323.22 327.78
API 36.20 36.3 35.6 35.3 35.1 34.6
SG (15 °C) 0.8438 0.8433 0.8468 0.8483 0.8493 0.8520
CI D4737 44.1 44.6 44.5 45.0 45.9 46.3
CI D976 44.2 44.9 44.9 45.6 46.9 47.7
DCN D6890 41.84 ± 0.12 42.89 ± 0.11 43.94 ± 0.16 45.17 ± 0.20 46.11 ± 0.32 47.04 ± 0.46
3812 N. Bezaire et al. / Fuel 89 (2010) 3807–3813

Fig. 7. Distillation curve for 1%, 2%, and 5% aged biodiesel in ULSD.
Fig. 9. Distillation curve for 0.01%, 0.1% cold flow additive (CFA) in ULSD.

Table 4
Table 5
Distillation temperatures (°C), API gravity, density, cetane index, and derived cetane
Distillation temperatures (°C), API gravity, density, cetane index, and derived cetane
number for 1%, 2%, and 5% blends of oxidized biodiesel (OBD) in ULSD.
number for ULSD with 0.01 and 0.1 wt.% cold flow additives (CFA).
Property 1% OBD 2% OBD 5% OBD
Property #2 ULSD 0.01% CFA 0.10% CFA
IBP 186.67 187.45 187.39
IBP 185.22 181.33 182.38
T10 20,322 20,383 20,378
T10 202.28 201.94 201.67
T50 25,144 25,272 25,572
T50 246.01 245.39 245.78
T90 31,061 31,406 31,850
T90 302.11 302.83 303.33
API 36.2 36 35.7
API 36.2 35.9 36.2
SG (15 °C) 0.8438 0.8448 0.8463
SG (15 °C) 0.8438 0.8453 0.8438
CI D4737 44.7 44.7 44.9
CI ASTM D47437 44.1 43.5 44.1
CI D976 44.9 44.4 44.5
CI ASTM D976 44.2 43.4 44
DCN D6890 45.45 ± 0.11 47.79 ± 0.24 49.53 ± 1.56
DCN ASTM D6890 41.84 ± 0.12 42.98 ± 0.07 45.36 ± 0.06

curves for each blend varied only slightly from each other with the to the next, while the DCN increased significantly. An increase of
curves for the larger concentrations appearing higher. 8% in the derived cetane number was observed for oxidized biodie-
Table 4 displays the distillation temperature for each of the sel blended at 5% in ULSD versus fresh B5. The cetane index, how-
aged biodiesel blends at various points of recovery as well as ever, does not accurately predict this increase.
values for API gravity, specific gravity at 15 °C (SG), cetane index The derived cetane number is based upon the ignition delay
(CI) determined by ASTM D4737 and D976 and the derived cetane which heavily depends on chemical properties of each fuel such
number (DCN). The comparison of cetane index to derived cetane as the presence of free radical initiators and oxygenated com-
number is illustrated in Fig. 8. pounds. It is expected that aged biodiesel will oxidize and form
As shown in Eqs. (1) and (2), both methods for cetane index are free radical initiator components, such as hydroperoxides
based upon measurements of physical parameters such as boiling [18,35,37,38]. These chemical species would cause a decrease in
point, API, and density. The API gravity of the aged biodiesel at dif- the ignition delay which would result in an increase in the derived
ferent concentrations did not vary by more than 0.5. Likewise, the cetane number [18,35]. If the concentration of aged biodiesel is in-
variation of distillation curves for all of the fuels was very small. As creased, the amount of peroxide components in the fuel would also
a result, as shown in Fig. 8, the cetane index calculated by both increase, allowing the combustion to occur more rapidly. The ce-
ASTM D4737 and ASTM D976 only varied slightly from one fuel tane index methods do not display the effects of these products.
The derived cetane number has been shown to reflect the change
in combustion more accurately than cetane index.

3.2.4. ULSD with winter additives

Fuel additives have been used not only to decrease the draw-
backs such as, low lubricity, low ignition quality and poor cold flow
properties, but also to produce specified fuels that meet interna-
tional standards like ASTM D 6751, and, EN 14214. Additives im-
prove ignition and combustion efficiency, stabilize fuel mixtures,
protect the motor from abrasion and wax deposition, and reduce
pollutant emissions, among other features. Such an additive used
in North America during winter weather conditions (after Novem-
ber 1) is Cold Flo 600RK, which contains, cold flow improvers, ce-
tane improvers and lubricity improvers. The effect of this
additive on the cetane measurement methods was also investi-
gated. A boiling curve for 0.01 and 0.1 wt.% cold flow additive
Fig. 8. Comparison of cetane index by ASTM D4737 and ASTM D976 to derived (CFA) in ULSD was constructed and is illustrated in Fig. 9 and, Table
cetane number for aged biodiesel in concentrations of 1%, 2%, and 5% in ULSD. 5 displays the distillation temperature for each of the additized
 N. Bezaire et al. / Fuel 89 (2010) 3807–3813 3813

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[13] ASTM D6890-08. Standard test method for determination of ignition delay and
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