QUANTITATIVE EVALUATION OF AN ON‐HIGHWAY TRUCKING
FLEET TO COMPARE #2ULSD AND B20 FUELS AND THEIR
IMPACT ON OVERALL FLEET PERFORMANCE
C. R. McKinley, J. H. Lumkes Jr.
ABSTRACT. A study was performed on 20 Class‐8 trucks paired by make, model, mileage, and drive cycles. Ten trucks were
operated using #2 Ultra‐Low Sulfur Diesel and 10 using a 20% soy methyl ester blend (B20). All trucks were equipped with
data collection units that monitored engine information including fuel consumption, idle time, truck speed, engine load, and
engine speed. Data collection occurred over a continuous span of 12 months. In addition to operating data, laboratory‐based
fuel and engine oil testing was performed to quantify the analytical differences between the two fuel types. Cetane number,
energy content, density, kinematic viscosity, and lubricity was measured for both fuels and at every oil service interval engine
oil samples were evaluated based on fuel dilution, soot content, wear metals, contaminant metals, viscosity, oxidation, and
acid/base number. Operational and maintenance issues such as cold start reliability, fuel filter service intervals, and general
engine maintenance was also analyzed for each fleet. Statistical analysis was performed to determine significant differences
in the performance of engines on these #2ULSD and B20 fuels. At the conclusion of the study minimal differences were found
with most comparisons, the exceptions primarily found in differences between the engine oil samples based on the two fuel
types used in the study. These differences included viscosity, acid/base number, oxidation, and lead wear which indicated
slightly higher oil degradation levels with B20 use.
Keywords. Biodiesel, Biofuel, B20, Fleet, Diesel, Renewable fuel, Alternative fuel, Class 8 truck, Fuel economy, Oil analysis,
he concept of using biodiesel in compression (Energy, 2007). Of particular note, the minimum requirement
ignition engines has been around for the past for biomass‐based diesel, namely biodiesel, is set for
century. Yet, it has only been within the past decade 0.5 billion gal (1.9 billion L) in 2009 and increases to 1
that biodiesel consumption has seen a reasonable billion gal (3.8 billion L) in 2012.
amount of growth. With the recent legislation mandates, Diesel engine original equipment manufacturers (OEMs)
production facility investments, and `home‐grown' are beginning to understand that more and more of their
advertisements, biodiesel has become a viable alternative to customers are going to run blends of biodiesel, from 1% to
petroleum derived diesel fuel. Consumers are requesting less 100%, in their diesel engines. As of January 2008, the
expensive, renewable energy sources to fuel their vehicles, majority of diesel engine OEMs have announced the
power their cities and homes, and transport goods to and from approval of various levels of biodiesel. Nineteen current
their businesses. The increase in fuel prices has stirred up engine manufacturers have approved biodiesel blends
consumer vulnerability concerns of being significantly ranging from B5 to B100 for various engine applications
dependent on a sole energy form – petroleum derived fuel. (NBB, 2008). There are five foreign automotive companies
One of the main benefits of biodiesel expansion is that it producing diesel engines for passenger car or light duty
contributes to energy security by lessening the demand on applications that have plans to release their vehicles into the
imported oil. The Renewable Fuel Standard, Section 202 of U.S. market in the near future, but have not yet announced a
the Energy Independence and Security Act of 2007, release for biodiesel. The fuel injection equipment (FIE)
mandates that 11.1 billion gal (42.0 billion L) of renewable manufacturers released a common position statement
fuels are to be consumed in the year 2009 with increasing indicating release of their injection equipment for admixtures
annual increments through 2022 when 36 billion gal up to a maximum of 5% fatty acid methyl ester, meeting the
(136 billion L) of renewable fuels are to be consumed EN14214 standard, with unadulterated diesel fuel, meeting
the EN590 standard. The final product, B5, must also comply
with EN590 (FIE Manufacturers, 2004). One major concern
about the use of biodiesel is in regard the quality of the fuel.
Submitted for review in November 2008 as manuscript number PM BQ9000 is a cooperative and voluntary national biodiesel
7798; approved for publication by the Power & Machinery Division of
ASABE in February 2009.
accreditation program for both producers and marketers of
The authors are Cody R. McKinley, ASABE Member Engineer, biodiesel that was established to help assure that biodiesel
Graduate Student, and John H. Lumkes, ASABE Member Engineer, fuel is produced to and maintained at the industry standard,
Professor, Department of Agricultural and Biological Engineering, Purdue ASTM D6751 for B100 and to promote the commercial
University, West Lafayette, Indiana. Corresponding author: John H.
success and public acceptance of biodiesel. ASTM has
Lumkes, Department of Agricultural and Biological Engineering, 225 S.
University St., Purdue University, West Lafayette, IN 47907; phone: recently announced a new specification release, ASTM
574‐595‐0060; fax: 765‐496‐1115; e‐mail: email@example.com. D7467, for B6‐B20 finished fuel blends which identifies
Applied Engineering in Agriculture
Vol. 25(3): 335‐346 E 2009 American Society of Agricultural and Biological Engineers ISSN 0883-8542 335
numerous testing specifications that the biodiesel blend must Chase et al. (2000) demonstrated the use of a 50% blend
meet in order to be considered an acceptable quality fuel. The of hydrogenated soy ethyl ester (HySEE) with 50% #2 diesel
specification was established through combined efforts and fuel for over 322,000 km (200,000 miles) in a heavy duty
inputs of engine manufacturers, petroleum and biodiesel Class 8 truck with a Caterpillar 3406E engine. Over
producers, government representatives, researchers, and 144,000 L (38,000 gal) of B50 were consumed during the
academics. BQ9000 and the ASTM D7467 standard have study. No accelerated engine degradation was detected from
been implemented to help augment the availability of high the engine oil analysis and extensive inspection of engine
quality biodiesel blends in the marketplace. components upon completion of the study showed acceptable
A significant amount of research has been done on the wear.
various aspects of operating a compression ignition engine Fraer et al. (2005) reported on the operation of four 1993
with various blends of biodiesel and certain general trends Ford cargo vans and four 1996 Mack tractors, two of each
have emerged from this research. Torque and horsepower running on B20 and two on #2 diesel, belonging to the United
values of an engine tend to decrease slightly with an States Postal Service (USPS). After four years of operation
increasing amount of biodiesel and fuel economy is directly and more than 965,000 km (600,000 miles) accumulated with
proportional to the volumetric lower heating value of the B20 vehicles, the engines and fuel systems were analyzed to
fuel, which typically decreases with increasing amounts of compare wear characteristics. No differences in wear were
biodiesel (Graboski and McCormick, 1998). Exhaust gas discovered during the engine teardown and little difference
emissions CO, total hydrocarbon (THC), and particulate was found in operational and maintenance costs between the
matter (PM), tend to decrease with increasing amounts of two groups that could be attributed to the fuel type. The Mack
biodiesel while levels of NOx tend to increase slightly (US tractors operating on B20 were, however, found to have
EPA 2002). Blends of biodiesel in diesel fuel, even as little significant problems with the biodiesel blend, resulting in
as 2%, can significantly increase the lubricity of the fuel repeated fuel filter plugging. These tractors also required
(Schumacher 2005a). Biodiesel tends to be incompatible injector nozzle replacement which may have been attributed
with older seal materials, especially nitrile, causing them to to out‐of‐specification fuel.
swell and/or fail, but the fluorinated elastomers that most Proc et al. (2006) studied nine identical in‐use 40‐ft
engine manufacturers have been using in their engines for the passenger transit buses powered by Cummins ISM engines,
last decade are able to tolerate this fuel (Graboski and five of which operated on B20 and the other four on #2 diesel
McCormick, 1998). fuel, for a period of two years. There was no difference
A variety of extended use biodiesel fleet studies have been between the average on‐road fuel economy between the two
reported since the 1990s. Malcosky and Wald (1997) studied fleets, but lab testing indicated a 2% average reduction in fuel
10 Navistar‐International dump truck/snow plows for economy for the B20 vehicles. Laboratory emissions testing
9 months; five operating on B20 and another five on #2 diesel indicated reductions in all measured pollutants which
fuel as a baseline. This study focused on collecting and included THC, CO, PM, and even NOx. Occasional fuel filter
analyzing detailed operational and reliability data. The B20 plugging events that occurred for the B20 fueled busses were
fleet accumulated over 97,000 km (60,000 miles) and likely the result of out‐of‐specification biodiesel. The engine
consumed 33,300 L (8,800 gal) of fuel at the time of the and fuel system maintenance costs were found to be nearly
report. This study indicated that proper fuel blending identical for the two groups. Engine oil analysis indicated no
techniques were important for obtaining homogenous 20% additional wear metals and significantly lower soot levels
blends of biodiesel. Operation of the B20 fleet was from the B20 fueled busses.
accomplished without encountering any major problems and While a number of biodiesel fleet studies have been
no significant differences in engine power or visible smoke published over the past few years, there have been very few
were observed between the two fleets. quantitative studies of in‐use Class 8 over‐the‐road trucks
Peterson et al. (1999) reported a 161,000‐km comparing B20 and #2 ultra low sulfur diesel (#2ULSD).
(100,000‐mile) operation of an on‐the‐road pickup truck with This study evaluates the performance of #2ULSD and B20 in
a 5.9‐L Cummins engine operating with a 20% rapeseed relatively new model year, electronically injected engines
methyl ester (RME) blend. The truck used a significant and compares the differences in the two fleets in terms of fuel
number of fuel filters to continuously solve a power loss economy, fuel properties and fuel quality, engine oil analysis,
problem due to filter plugging over the duration of the study. and general service and operation for a fleet of Class 8
Engine oil analysis and teardown analysis indicated no over‐the‐road trucks.
abnormal wear or performance and no unusual deterioration Results from a similar study performed with 10 Class 8
of the engine components. trucks with C‐13 Caterpillar engines operating on B20 and
Four road maintenance trucks with Cummins M11 diesel another matching 10 units operating on #2ULSD have shown
engines operated on B20 for 17 months in Minnesota (Bickel slightly lower, but not statistically significant, fuel economy
and Strebig, 2000). Two identical trucks operated on 100% with the B20 fleet (Heck, 2007). A noticeable difference
diesel fuel for a baseline comparison. Nearly 95,000 L between the two groups was the significant number of
(25,000 gal) of B20 were consumed over the course of the additional fuel filters that needed replaced in the B20 group
study and the B20 trucks had the same fuel consumption rate due to premature filter plugging. The blending procedure for
as the baseline trucks. Special care was taken to make certain the biodiesel was changed and the number of filter plugging
all fuel was mixed with cold flow improvers, #1 diesel fuel incidents decreased significantly. Research was performed
and additives, to ensure continuous cold weather operation. on various blends of B20 with #1 diesel and commercial cold
No unusual engine wear or fuel dilution was detected from oil flow additives in an attempt to further reduce the number of
samples that were collected every 8,000 km (5,000 miles). plugged fuel filters.
336 APPLIED ENGINEERING IN AGRICULTURE
Table 2. Average vehicle operating parameters (Aug‐Dec).
Twenty Class 8 trucks were evaluated during the calendar Average Parameters #2ULSD Fleet B20 Fleet P‐Value[a]
year of 2007 to quantify the differences between #2ULSD Number of observations 212 213 N/A
and B20. Ten of the trucks operated with #2ULSD and Idle time (%) 17.6% 17.7% 0.9065
10 unmodified trucks of identical make and model operated Vehicle speed (MPH) 45.1 44.7 0.3275
with B20. The biodiesel used in the B20 fuel was a soy methyl Engine load (%) 38.5 38.0 0.2175
ester (SME). The trucks that operated with #2ULSD are Engine speed (RPM) 1290 1283 0.3760
identified numerically throughout this report (1, 2, 3, etc.) [a] Based on two‐tailed, unpaired t‐tests.
and the trucks that operated with B20 are identified in the
same numerical fashion, but with the letter B following the
truck number (eg. 1B, 2B, 3B etc.) A detailed description of 12 months during 2007. Additional data such as percent
each truck and can be found in table 1. idle time, vehicle speed, engine speed, and engine load were
Trucks returned to the fleet transportation center on a daily collected through the same remote data system, but only for
basis to ensure they were being fueled with consistent fuel the second half of the year (August – December). It has been
throughout the study. All trucks were equipped with Fuller suggested that the fuel economy data as indicated by the
10‐speed FR14210B transmissions and 11R 22.5 tires. The ECM may be slightly lower than the actual fuel economy
trucks that were analyzed in this study were not only identical until a truck has accumulated approximately 233,000 km
by model year, manufacturer, transmission, and tire size, but (145,000 miles) (Cummins Inc., 2007). However, the trucks
they were also paired based upon their similarities with that were monitored that started the study under 233,000 km
respect to loading conditions, driving cycle, and trip (145,000 miles) should exhibit only minor errors (<3%) in
distances. This was done to eliminate as many external fuel economy and any error should have been almost
variables as possible so that the focus could remain on the identical for each fleet. The trucks all surpassed 233,000 km
dependant variable at hand; fuel type. Vehicle speed, load, (145,000 miles) within the first few months of the study. For
and engine speed data was provided in a histogram format verification purposes, the fuel economy of six trucks (4‐B20
through vehicle data collection units. This data was and 2‐#2ULSD) was measured by recording the volume of
downloaded weekly for all 20 trucks from mid‐August until fuel consumed and distance driven over five consecutive fuel
late‐December. Since the vehicle speed, load, and engine tank fill‐ups and then compared with the ECM‐derived fuel
speed data were given in a histogram format their averages economy for the same period. The average difference
were calculated by summing the average value of the bin between the manually determined fuel economy and the
range multiplied by the percent of vehicle on time for that ECM fuel economy was 1.16% which is less than 0.04 km/L
particular week. Averages for vehicle idle time, vehicle (0.1 mpg). Average fuel economy data for both fleets can be
speed, engine load, and engine speed were calculated from found in figure 1. The average fuel economy for the B20 fleet
this data (table 2). This data demonstrates the paired nature over the 12‐month period was 2.96 km/L (6.97 mpg) with a
of the driving cycles and load conditions for the two fleets. standard deviation of 0.20 km/L (0.46 mpg), while the
Each truck operated on a freeway driving cycle and average fuel economy for the #2ULSD fleet was 2.94 km/L
accumulated approximately 4,800 km (3,000 miles) per (6.91 mpg) with a standard deviation of 0.17 km/L
week. The #2ULSD fleet accumulated 2,453,607 km (0.41 mpg). The fuel economy data was statistically
(1,524,601 miles) and the B20 fleet accumulated 2,433,713 analyzed by an unpaired, two‐tailed t‐test at a 95%
km (1,512,239 miles) over the 2007 calendar year. confidence interval (a = 0.05) and the difference in fuel
economy was not found to be statistically significant
(P‐value of 0.379). Other fleet analysis studies have shown
similar fuel economy results (Bickel and Strebig, 2000; Proc
FUEL ECONOMY et al., 2006).
The fuel economy data was collected using a remote A significant trend over time was noticed. The fleet
vehicle tracking and diagnostic management system. Data average fuel economy was significantly higher in the warmer
was collected from the engine electronic control module months of the year and comparatively lower in the colder
(ECM) via this management system and recorded for months of the year. Figure 2 shows the correlation between
Table 1. Fleet vehicle descriptions.
Truck ID[a] Model Year and Manuf. Engine Type Rated Power, kW (Hp) Rear Axle Ratio
1 & 1B 2003 9200I International ISM Cummins 276 (370) 3.08:1
2 & 2B 2004 VNM64T Volvo VE D12 Volvo 295 (395) 3.08:1
3 & 3B 2005 VNM64T Volvo VE D12 Volvo 295 (395) 2.93:1
4 & 4B 2005 VNM64T Volvo VE D12 Volvo 295 (395) 2.93:1
5 & 5B 2005 VNM64T Volvo VE D12 Volvo 295 (395) 2.93:1
6 & 6B 2005 VNM64T Volvo VE D12 Volvo 295 (395) 2.93:1
7 & 7B 2005 VNM64T Volvo VE D12 Volvo 295 (395) 2.93:1
8 & 8B 2006 VNM64T Volvo VE D12 Volvo 324 (435) 2.79:1
9 & 9B 2007 VNM64T Volvo VE D12 Volvo 324 (435) 2.79:1
10 & 10B 2007 VNM64T Volvo VE D12 Volvo 324 (435) 2.79:1
[a] Trucks 1, 2, 3‐ &10 operated with #2ULSD and trucks 1B, 2B, 3B‐ &10B operated with B20.
Vol. 25(3): 335‐346 337
monthly fleet fuel economy (all 20 trucks) and ambient air 4.5 L (0.5 to 1.2 gal) of fuel are consumed for every hour of
temperature which was obtained from a weather station idle time for heavy duty truck engines depending heavily on
located near the fleet transportation center. The monthly the accessories that are being powered during idle and the
average ambient air temperature was determined by taking engine idle speed (Pekula et al., 2003). However, it can be
the mean of the daily high and low temperatures over the seen in figure 3 that although the average percent idle time
entire month. for the entire fleet stayed almost constant from the months of
For every 5.6°C (10°F) increase in ambient air September to November there was still a significant decrease
temperature, fuel economy for these particular trucks in fuel economy. While overall fuel economy will decrease
increased by 0.06 km/L (0.13 mpg), or approximately 2%. A with an increased percentage of idle time, this figure
12% increase in total fleet average fuel economy was seen demonstrates that the majority of the fluctuation in fuel
from the coldest month to the warmest month of the study. economy throughout this study was caused by ambient air
This was most likely due to the reduction in aerodynamic temperature rather than engine idle time.
drag from the lower density ambient air in the warmer
months. Results similar to this have been reported in previous FUEL ANALYSIS
studies (Wood and Bauer, 2003; Cummins Inc., 2007). Laboratory analysis was performed on both B20 and
Much of the weather dependency has historically been #2ULSD fuel samples. Tests were chosen based on the
attributed to increased engine idle time as roughly 1.9 to analytical fuel properties that have the most significant
Figure 1. Average fleet fuel economy for the 2007 calendar year.
Figure 2. Linear relationship between fuel economy and ambient air temperature.
338 APPLIED ENGINEERING IN AGRICULTURE
ÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕ B20 Fleet #2ULSD Fleet % Idle Time
ÕÕÕÕÕÕÕÕÕÕÄÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕ 3.15 40
Average Fleet Fuel Economy (km/L)
ÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕÕ 3.10 35
Average Fleet % Idle Time
ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ
ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ
Ä ÄÄ ÄÄ ÄÄ ÄÄ 2.80
ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ 2.75 5
ÄÄ ÄÄ ÄÄ ÄÄ ÄÄ
Ä ÄÄ 2.70 0
Figure 3. Average truck idle time displayed with fuel economy data for 5 months.
impact on engine durability, combustion performance, and with cetane numbers above 50. Fuels with cetane numbers at
fuel injection equipment compatibility. One sample of each or below 45 have been known to modestly increase certain
type of fuel was tested so no statistical significance can be exhaust emissions and decrease engine output power
determined from this testing (table 3). (Ladommatos et al., 1996; Icingur and Altiparmak, 2003).
Low cetane fuels can also cause hard starting and rough
Kinematic Viscosity engine operation. The ASTM D975 standard for diesel fuel
The viscosity values both fell within the ASTM D975 and and D7467 standard for B20 both require a minimum cetane
D7467standard viscosity range for diesel fuel and B20 of number of 40 and most engine manufacturers in the United
1.9‐4.1 cSt. The kinematic viscosity of the B20 was slightly States designate a minimum cetane number, typically
higher than that of the #2ULSD. Long‐term use of between 40‐50, for their engines to operate properly (Knothe,
excessively high viscosity fuels can lead to excessive injector 2005).
coking which results in deterioration of engine performance
(Peterson et al., 1987). Low fuel viscosity can lead to Cold Filter Plug Point
excessive leakage and increased fuel pump and injector wear Cold filter plug point (CFPP) was slightly lower for the
(Hansen et al., 2001). B20 fuel samples that were taken in both August 2007 and
February 2008. The storage location for the #2ULSD was in
Cetane Number the existing underground bulk storage fuel tank. Conversely,
Ignition quality within the engine would be essentially the B20 was kept in a 16,600‐L (4,400‐gal) temporary
equivalent for these two fuels because the cetane numbers of above‐ground storage tank for the entirety of the study. The
B20 and #2ULSD were similar. Ignition quality refers to the B20 storage tank fuel filter plugged and created a problem
time delay between the start of injection and the start of with pumping the B20 from the above ground tank into the
combustion; also known as combustion delay. The cetane trucks for refueling for a two‐week period during the year
numbers for both samples are higher than typical #2ULSD, preventing the trucks from operating on B20. This occurred
which is in the high 40's. Modern diesel engines operate well during the 2 coldest weeks of the year in February 2007. With
the exception of 3 of these 14 days, the daily low temperature
Table 3. B20 and #2ULSD fuel analysis[a].
was below ‐18°C (0°F) and the coldest temperature
experienced during this time period was ‐22°C (‐9°F).
Property Test Method B20 #2ULSD
However, throughout the study, no trucks had starting issues
Kinematic viscosity @ 40°C (cSt) D445 2.875 2.370 due to cold weather filter plugging.
Cetane number D613 56.4 55.6
C.F.P.P. (Aug 2007) (°C) D6371 ‐18 ‐14 Heat of Combustion (HOC) and Density
C.F.P.P. (Feb 2008) (°C) D6371 ‐33 ‐26
The energy density, or heat of combustion values, of the
Density @ 60°F (g/mL) D4052 0.8545 0.8349 two fuels were similar (within 1.3% on a mass or volumetric
Heat of combustion (mass) (MJ/kg) D240 44.72 45.30 basis). Although biodiesel typically has a lower mass based
Heat of combustion (vol) (kJ/mL) Calculated 38.21 37.82 HOC value the higher density of the B20 made up the
Lubricity (HFRR) (μm) D6079 230 450 difference to keep the volumetric based HOC values similar.
[a] One sample of each fuel was tested. The HOC values are specified as net heating value rather than
gross heating value. Net heating values are used when
Vol. 25(3): 335‐346 339
discussing internal combustion (IC) engines because net Table 4. B20 fuel quality results.
assumes that the latent heat of vaporization of water is not D7467
recovered, which is representative of what happens in an IC Property Test Method Value Limit[a]
engine. Cloud point (°C) D2500 ‐18.2 Report[b]
Ash (mass %) D482 <0.001 0.01 max
Lubricity Sulfur (ppm) D5453 7.9 15 max
Lubricity testing was performed per ASTM D6079 via a Particulate contamination (ppm) D6217 0.6 --
high frequency reciprocating rig (HFRR) test. The wear scar Karl Fisher water (ppm) D6304 109 --
diameter (WSD) for the B20 was almost half of that for the Acid value (mg KOH/g) D664 0.09 0.3 max
#2ULSD fuel. The long hydrocarbons and polarity of Ca (ppb) D7111 106 --
biodiesel make it a good candidate for improving the K (ppb) <500 --
lubrication properties of #2ULSD. The maximum allowable Mg (ppb) <100 --
wear scar diameter per ASTM D975 and ASTM D7467 is
520 μm, while fuel injection manufacturer, Bosch, Na (ppb) <500 --
recommends the use of a fuel with a WSD ≤ 460 μm (Robert Flash point (°C) 60.6 52 min
Bosch GmbH, 2004). While no short‐term effects were Oxidation stability (h) EN14112 6.1 6 min
witnessed, long‐term benefits on the fuel injection equipment Interfacial tension (mN/m) D971 10.64 --
may be observed with the increased lubricity of B20. Derived cetane number D6890 52.3 --
Biodiesel concentration (%) D7371 18.3 6 to 20
Fuel Quality [a] Denotes an additional quality test, but no limit specified in ASTM
Another set of fuel tests were performed on a B20 sample D7467.
[b] Cloud point to be reported by fuel manufacturer.
to determine the quality of the fuel and to see how it
compared to some of the recently proposed ASTM B6‐B20
specifications. Supplementary quality tests that are not compression and oil rings and into the crankcase resulting in
specified in the D7467 standard were performed on this degradation of the engine oil. Oil samples were studied in
sample as well. This fuel sample was sent to the National order to determine the effects of the two fuel types on oil
Renewable Energy Laboratory (NREL) and the results from protection and degradation levels (table 5). Engine oil
this testing can be found in table 4. analysis was performed at each oil change interval, which
The B20 fuel sample that was submitted to NREL met the occurred at 48,300 km (30,000 miles). The analysis included
specifications that were tested as set forth by the ASTM percent fuel dilution, percent soot content, wear metal
D7467 limits for B6‐B20. The biodiesel concentration for the detection, additive and contaminant metal detection, oil
B20 sample was 18.3%. It was expected that the B20 used in viscosity, acid and base numbers, and oxidation and nitration
this study would consistently be near a 20% biodiesel blend values. A total of 54 used oil samples were collected and
because the fuel supplier used rack‐injection blending measured for the B20 fleet and the same was done for 57 used
techniques rather than the splash blending method, which oil samples from the #2ULSD fleet. Chevron Delo 400
tends to produce less consistent biodiesel blends Multigrade SAE 15W‐40 engine oil was used in both fleets.
(McCormick et al., 2005). It is also important to note that all
of the biodiesel used to blend the B20 came from a BQ9000 PHYSICAL AND CHEMICAL ANALYSIS
certified supplier. No statistical significance was found with the fuel
dilution, soot content, and nitration values for the two fleets.
This indicates that the fuel type did not have an impact on
these particular properties. However, recent studies have
ENGINE OIL ANALYSIS shown that the typical detection methods for percent fuel
Engine lubricating oil is an important component to both dilution for diesel fuel may not work as well with biodiesel
the immediate operability of an internal combustion engine blended fuels (Fang et al., 2006; Andreae et al., 2007).
as well as the lasting durability and longevity of the engine. Therefore, the fuel dilution testing may not be as accurate as
Engine lube oil not only protects vital components from anticipated.
wearing, but also reduces friction and keeps internal engine There were significant differences in the oil samples for
parts within their operational temperature limits. Unburnt viscosity, acid and base numbers, and oxidation values. The
fuel and combustion by‐products can seep past the piston kinematic viscosity value for new Delo 400 is around 15.1 cSt
Table 5. Physical and chemical properties of engine oil samples.
% Fuel Dilution % Soot Content Viscosity (cSt) Acid # Base # Oxidation Nitration
ASTM E2412[a] ASTM E2412[a] ASTM D445 ASTM D4739 ASTM D4739 ASTM E2412[a] ASTM E2412[a]
Fuel type #2ULSD B20 #2ULSD B20 #2ULSD B20 #2ULSD B20 #2ULSD B20 #2ULSD B20 #2ULSD B20
Avg. value 0.62 0.54 0.48 0.43 13.8 13.1 3.40 3.79 6.43 6.00 11.0 15.0 16.8 17.5
Std. dev. 0.34 0.21 0.30 0.28 0.64 0.53 0.91 1.08 0.95 1.12 3.21 4.37 4.61 4.52
P‐value[b] 0.1601 0.3579 < 0.0001 0.0441 0.0314 < 0.0001 0.4243
Stat. diff.?[c] No No Yes Yes Yes Yes No
[a] ASTM E2412 ‐ Standard practice for condition monitoring of used lubricants by trend analysis using fourier transform infrared (FT‐IR) spectrometry.
[b] Based on two‐tailed, unpaired t‐tests; 54 samples from B20 fleet and 57 samples from #2ULSD fleet.
[c] Statistical difference at a 95% confidence interval (α = 0.05).
340 APPLIED ENGINEERING IN AGRICULTURE
at 100°C. The average viscosity of the B20 fleet oil samples the metallic wear surfaces in the engine (Polaris
was lower than that of the #2ULSD by 0.7 cSt. The #2ULSD Laboratories, 2008a). The initial values for zinc and
fleet average indicated an 8.6% viscosity reduction from the phosphorus content in fresh Chevron Delo 400 oil are 1480
original value while the B20 average showed a 13.2% and 1360 ppm, respectively. Additive metal data can be
reduction. The three most common causes for a decrease in found in table 7. The fuel type effects found with zinc and
engine oil viscosity are fuel dilution, breakdown of viscosity phosphorus could be due to biodiesel's tendency to bond to
index (VI) improver additive, and overheating (Mayer, ZDDP. However, the difference in zinc and phosphorus for
2006b). Fuel dilution and VI additive breakdown are the two these two fleets was minimal and could have possibly been
most likely explanations for the decrease in oil viscosity for caused by the imprecision of the detection equipment or
this study. However, these lower viscosity levels were still minor variations in the oil manufacturing process. Still, new
within the acceptable range for engine oil viscosity. For this diesel engines using post‐injection regeneration strategies
particular engine oil, a viscosity under 11 cSt is considered for diesel particulate filters (DPF) could see higher fuel
abnormal and engine wear may be expedited once this point dilution rates and this could potentially have adverse
has been reached. Gateau (2006) reported viscosity values consequences on the effectiveness of ZDDP when using
that were lower by a similar quantity for a 12‐year evaluation biodiesel blends (Fang et al., 2007).
of heavy duty trucks operating on 50% rapeseed oil methyl Contaminant metals, silicon, sodium, and potassium were
ester (RME). Oil change intervals were 30,000 km also monitored and no statistical significance was found
(18,641 mi) for Gateau's study. between the two fleets for any of these metals. The high levels
Acid and base numbers of the oil samples were affected by of sodium and potassium, as indicated by the large standard
fuel type. The B20 fleet oil samples, on average, had higher deviations, came from one particular make and model year.
acid numbers (AN) and lower base numbers (BN) than the
#2ULSD fleet oil samples. The base number is a direct ELEMENTAL ANALYSIS
measurement of the alkaline reserve of the oil. When the acid Elemental analysis was performed in accordance to the
number of the oil sample is higher than the base number the ASTM D5185 standard for determination of additive
oil is no longer capable of neutralizing acids. Modern diesel elements, wear metals, and contaminants in used lubricating
engine oils typically have a starting BN between 8 and 13. oils by inductively‐coupled plasma atomic emission
The starting BN for Delo 400 Multigrade SAE 15W‐40 is spectrometry (ICP‐AES). Wear metal data can be found in
12.2. It is recommended that diesel engine oil be changed table 6, contaminant metal data in table 7, and typical metal
when the BN is half of the new oil (Mayer, 2006a; Polaris source data in table 8. Of the five metals analyzed, lead was
Laboratories, 2008b). This general guideline would indicate the only one significantly affected by fuel type (p < 0.001).
that the oil is to be changed when the base number reaches 6.1 There were two trucks in the B20 fleet, 1B and 2B, that
or below; the average for the B20 samples was 6.0. accounted for the majority of the lead wear. These trucks had
Oxidation measures the breakdown of the engine oil due accumulated over 804,000 km (500,000 miles) at the time of
to age and operating conditions. Oxidation values of the oil sampling and it is likely that the lead contamination came
samples were significantly larger for the B20 fleet (15 vs. 11); from a rod or main bearing starting to wear. It is difficult to
however, only engine oil oxidation values of 25 or higher say whether or not the fuel type had an impact on this wear
indicate abnormal oxidation. The oxygen content in or if it was just normal bearing wear. As stated earlier, it is
biodiesel could possibly have an impact on the oxidation of important that the base number of the oil remain higher than
engine oil due to fuel dilution in the B20 oil samples. Engine the acid number because acidic substances are especially
oil analysis in Bickel and Strebig (2000) also found that there harmful to soft metals such as lead. In samples where the acid
were several instances when trucks operating on B20 had number was greater than the base number (four samples for
“slightly high” values for fuel oxidation, while none were the #2ULSD fleet and five samples for the B20 fleet), the
observed in their baseline trucks which operated on #2 diesel average lead contamination was 22 ppm. Schumacher et al.
fuel. (2005b) and Agarwal et al. (2003) both describe studies in
Zinc dialkyldithiophosphate (ZDDP) is the source of zinc which many of the engine oil wear metals for vehicles
and phosphorus in engine oil. ZDDP is a polar additive that operating on biodiesel blends were found to be significantly
is responsible for bonding to the metallic surfaces in an less than those for vehicles operating on diesel fuel. This
engine to form a protective layer against wear. It has been particular make and model had critical levels of sodium and
claimed that the polar nature of biodiesel may attract potassium in both the #2ULSD and B20 fleets. The largest
available ZDDP molecules leaving less available to bond to
Table 6. Wear metal analysis of engine oil samples.
Wear Metals (ppm)[a]
Iron Lead Copper Aluminum Chromium
Fuel type #2ULSD B20 #2ULSD B20 #2ULSD B20 #2ULSD B20 #2ULSD B20
Avg. value 22.8 22.1 1.3 7.8 3.4 3.7 6.4 6.3 0.14 0.06
Std. dev. 10.7 8.6 2.3 13.8 3.9 2.8 2.9 2.9 0.35 0.23
P‐Value[b] 0.7152 0.0006 0.6436 0.8748 0.1557
Stat. Diff.?[c] No Yes No No No
[a] ASTM D5185 ‐ Determination of wear metals by inductively‐coupled plasma atomic emission spectrometry (ICP‐AES).
[b] Based on two‐tailed, unpaired t‐tests; 54 samples from B20 fleet and 57 samples from #2ULSD fleet.
[c] Statistical difference at a 95% confidence interval (α = 0.05).
Vol. 25(3): 335‐346 341
Table 7. Additive and contaminant metal analysis of engine oil samples.
Additive Metals (ppm)[a] Contaminant Metals (ppm)[a]
Zinc Phosphorus Silicon Sodium Potassium
Fuel type #2ULSD B20 #2ULSD B20 #2ULSD B20 #2ULSD B20 #2ULSD B20
Avg. value 1494 1436 1304 1259 6.5 5.1 38.5 12.1 26.6 11.4
Std. dev. 126 108 108 93 7.0 1.6 105.5 17.4 55.8 19.9
P‐value[b] 0.0111 0.0224 0.1557 0.0726 0.0623
Stat. diff.?[c] Yes Yes No No No
contaminant source of sodium and potassium was most likely constant. The B20 fleet used only 2.75 filters per month on
engine coolant. Engine coolant contamination issues are average for all 10 trucks and the #2ULSD fleet used 2.5 filters
independent of fuel type and are typically related to damaged per month on average. This equates to approximately
head gaskets, cylinder heads, liner seals, injector cups, or 72,000 km (45,000 miles) for fuel filter service life. A major
lube coolers. increase in filter usage was found in the month of October
A summary table of typical wear metal and contaminant 2006. The spike in filter usage in October 2006 for the B20
metal sources from heavy duty diesel engines can be found fleet was most likely caused by the solvent nature of B20
in table 8. cleaning out the residue in the truck fuel tanks. If this was the
only fuel change made it would be expected that the filter
usage would decrease back to normal after the first couple of
filter replacements. However, the filter usage remained
SERVICE, OPERATION, AND MAINTENANCE unusually high and, not long after, a major increase in filter
As stated previously, this particular fleet used a 16,600‐L
usage was found with the #2ULSD fleet starting in January
(4,400‐gal) aboveground tank for B20 storage during the
2007. Fuel filter usage increased to over 10 filters per month
testing period. The #2ULSD was stored in the pre‐existing
on average during 2007. This equates to approximately
belowground fuel tank. For two weeks during the month of
18,000 km (11,000 miles) for fuel filter service life, or a 75%
February the B20 would not flow from the above ground
reduction from early 2006 filter life. A history of fuel filter
storage tank into the truck fuel tanks due to supply filter
usage for both fleets can be found in figure 4.
plugging. The substance plugging the filter was a viscous,
The substance that caused the engine filter plugging was
off‐white, hazy compound similar to that described in Heck
identical for both fleets, yet much different from the
(2007). On these particular mornings, however, the trucks
substance that caused the supply filter plugging on the B20
that already had the B20 in their tanks did not have problems
storage tank in February. A thin, black film coated the engine
starting. Once the ambient temperature warmed slightly the
filter elements increasingly with mileage. Microscopic
tank supply filter was replaced and the B20 fleet resumed
pictures of a clean filter element section and a dirty filter
being fueled with B20. Bickel and Strebig (2000)
element section can be seen in figures 5a and 5b. The pictures
encountered no problems transferring B20 from an
shown are from a Fleetgaurd #FF5369 filter with a 20‐micron
underground tank to service vehicles for two winters in
rating at a 300X magnification level. Elemental analysis was
Minnesota. This may indicate that the storage method played
performed on this black substance and was found to contain
a significant role in the everyday operability of trucks using
83.24% carbon, 13.41% hydrogen, and 0.40% nitrogen. The
the B20 fuel.
common denominator for both fleets was the introduction of
Fuel filter usage was monitored throughout the study to #2ULSD and, therefore, is likely the cause of the excessive
determine the impact of the fuels on filter service life. In
fuel filter plugging issue. It is possible that a component of
order to properly study filter usage it was necessary to look
the #2ULSD is breaking down and falling out of solution,
at the previous year's filter service records for comparison. particularly when the fuel is introduced to the high
The two fleets were operating solely on #2 low‐sulfur diesel
temperatures and pressures, around 1,800 bar (26,000 psi), of
(#2LSD ‐ 500 ppm sulfur) until September 2006. At this point
the common rail injection systems and then recirculated back
the B20 fleet started operating on biodiesel blended with to tank. Excess fuel is recirculated back to tank to help with
#2ULSD to compose B20 and the #2ULSD fleet started
lubrication and cooling of the high pressure pump and
operating on #2ULSD (15 ppm sulfur). During the first three
injectors. Further investigation is needed to understand
quarters of 2006 the filter usage for each fleet was relatively
Table 8. Typical sources of wear and contaminant metals.
Metal Typical Sources
Wear metals[a] Iron Cylinder liner, iron pistons, gears, oil pump
Lead Rod and main bearings, bushings
Copper Rod and main bearings, bushings, lube oil coolers
Aluminum Engine piston, rod and main bearings
Chromium Piston rings, cylinder liners, exhaust valves
Contaminant metals[a] Silicon Dirt, grease, seals and gasket material, and lube oil additive
Sodium Engine coolant leak, salt water contamination
Potassium Engine coolant leak, lube oil additive, new coating on bearings
[a] Wear and contaminant metal source information obtained from Mayer 2006b and Polaris Laboratories ‐ Wear Metal Guide.
342 APPLIED ENGINEERING IN AGRICULTURE
Figure 4. Monthly fuel filter usage.
exactly what this black film is and to determine the cause of
The average fuel price for the entire year for the #2ULSD
was $0.74USD/L ($2.80USD/gal), while the average fuel
price for the B20 was $0.77USD/L ($2.93USD/gal). The
monthly fuel prices for B20 and #2ULSD, normalized to the
annual average #2ULSD price, can be found in figure 6.
While annual truck repair costs were relatively high for
general repair issues, no repair costs for either fleet were
incurred due to fuel‐related issues over the calendar year.
After evaluating 20 Class‐8 trucks for an entire calendar
year the overall differences with regards to fuel economy,
fuel test results, engine oil analysis, service and maintenance,
and fuel prices between the #2ULSD and B20 fueled trucks
Figure 5a. Clean filter element.
were found to be relatively minute. Each fleet accumulated
over 2.4 million km (1.5 million miles) during the 2007
calendar year and there was no difference in fuel economy for
the two fleets. Both fuel types were tested and compared with
fuel standards for performance and quality. Each sample met
or exceeded every ASTM specification tested. Many of the
Figure 5b. Plugged filter element.
Figure 6. 2007 monthly fuel prices.
Vol. 25(3): 335‐346 343
fuel properties such as energy content, density, viscosity, operating the trucks on B20 can be attributed to the
cetane number, and cold filter plug point were very similar maintained quality and integrity of the biodiesel.
for the two fuel types. The largest difference between the Engine oil analysis was performed at oil change intervals,
fuels was lubricity. The wear scar diameter of the B20 was which occurred at 48,000 km (30,000 miles). A total of 54 oil
almost half of that of #2ULSD when tested with the HFRR samples from the B20 fleet and 57 oil samples from the
method. As with any type of fuel, petroleum‐based or #2ULSD fleet were collected and analyzed. No differences
vegetable oil‐based, it is important that the quality of the fuel between the two fuel types were found with the following
is maintained within certain specifications and standards. tests: fuel dilution, soot content, and nitration. Fuel type did
The biodiesel used in the B20 blend came from a BQ‐9000 not affect the following wear metals: copper, aluminum, and
supplier and met the ASTM D6751 specification for B100. A chromium nor the following contaminant metals: silicon,
sample of B20 was tested and compared to the ASTM D7467 sodium, and potassium. However, fuel type did affect
quality standard for B6‐B20. The sample met or exceeded the viscosity, acid and base number, and oxidation. Lead was the
test specifications that were tested as set forth by the only wear metal that was statistically different for the two
standard. It is likely that the relative lack of issues with fleets and zinc and phosphorus, which come from the ZDDP
Table 9. Summary of on‐highway fleet analysis comparing B20 and #2ULSD fuels.
Aspect #2ULSD Fleet B20 Fleet Stat. Diff. Means[a] Comments
Fuel econ. Fleet travel, km (miles) 2,453,607 2,433,713 N/A Over 2.4 million km (1.5 million miles)
(1,524,601) (1,512,239) accumulated/fleet
Fuel economy, km/L (mpg) 2.94 2.96 No 12 mo. avg. for 10 trucks/fleet
Fuel testing Kinematic visc 40°C (cSt) 2.370 2.875 N/A Fuels met ASTM D975 and D7467 specs
Cetane number 55.6 56.4 N/A Fuels met ASTM D975 and D7467 specs
CFPP (Aug 2007) (°C) ‐14 ‐18 N/A CFPP for B20 sample lower during summer
CFPP (Feb 2008) (°C) ‐26 ‐33 N/A CFPP for B20 sample lower during winter
Density @ 60°F (g/mL) 0.8349 0.8545 N/A B20 had a slightly higher density
HOC (mass) (MJ/kg) 45.30 44.72 N/A B20 had a lower mass based heating value
HOC (vol) (kJ/mL) 37.82 38.21 N/A B20 had a higher vol. based heating value
Lubricity (HFRR) (μm) 450 230 N/A Fuels met ASTM D975 and D7467 specs
Engine oil % Fuel dilution (% vol) 0.62 0.54 No Standard fuel dilution testing may not be as
tests accurate when detecting B20
% Soot content (% vol) 0.48 0.43 No Similar soot content in oil samples
Viscosity (cSt) 13.8 13.1 Yes Viscosity lower for B20 samples; original oil
viscosity was 15.1 cSt
Acid number 3.40 3.79 Yes Lower acid number is better
Base number 6.43 6.00 Yes Higher base number is better; original oil base
number was 12.2
Oxidation 11.0 15.0 Yes Lower oxidation number is better
Nitration 16.8 17.5 No Lower nitration number is better
Engine oil Iron (ppm) 22.8 22.1 No Similar iron wear results
wear metals Lead (ppm) 1.3 7.8 Yes Two trucks with > 500,000 miles accounted
for majority of B20 fleet lead wear
Copper (ppm) 3.4 3.7 No Similar copper wear results
Aluminum (ppm) 6.4 6.3 No Similar aluminum wear results
Chromium (ppm) 0.14 0.06 No Similar chromium wear results
Engine oil Zinc (ppm) 1493.7 1436.1 Yes Wear prevention additive (ZDDP)
Phosphorus (ppm) 1303.6 1259.2 Yes Wear prevention additive (ZDDP)
metals Silicon (ppm) 6.5 5.1 No Similar silicon contaminant results
Sodium (ppm) 38.5 12.1 No Typically caused by coolant leak ‐
unrelated to fuel type
Potassium (ppm) 26.6 11.4 No Typically caused by coolant leak ‐
unrelated to fuel type
Service and Filter usage (filters/mo.)[b] 10.5 10.4 No #2ULSD was common denominator
maintenance in unusually high filter usage
Fuel price, USD/L $0.74 $0.77 N/A B20 cost was $0.03/L ($0.13/gal)
(USD/gallon) ($2.80) ($2.93) higher on average
Repair costs -- -- N/A Major fuel related repair costs were
[a] Statistical difference at a 95% confidence interval (α = 0.05).
[b] Data for 10 months in 2007.
344 APPLIED ENGINEERING IN AGRICULTURE
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