ENGINE PERFORMANCE
Background
Biodiesel methyl esters improve the lubrication properties ("lubricity")
of the diesel fuel blend. Long term engine wear studies have been
conducted in Europe and in the US. Porsche (Germany) determined
that neat (100%) Biodiesel reduced long term engine wear in test
diesel engines to less than half of what was observed in engines
running on current low sulfur diesel fuel. Lubricity properties
of fuel are important for reducing friction wear in engine components
normally lubricated by the fuel rather than crankcase oil.
Recently, requirements for reformulating "low
sulfur, low aromatic" diesel fuel have resulted in a decreased
in the lubricity of diesel fuel. The reduction in aromatics at
that time also changed the elastomeric properties of the fuel
resulting in the shrinking of gaskets, O-rings and seals in older
engines. Since then, truckers, boaters and other operators of
diesel engines have turned to a variety of petroleum additives
(in extreme cases, transmission fluid) in an attempt to protect
their engines from excessive wear and gasket leaks associated
with the new "low sulfur/low aromatics" diesel fuel.
More than 100 Biodiesel demonstrations, with over 10 million road
miles in trucks, have confirmed the performance benefits of this
fuel additive for emissions and mechanical lubricity. No adverse
durability or engine wear problems were found; in fact, in road
tests with heavy duty truck engines, engine wear was significantly
decreased after running 100,000 miles on blends of Biodiesel (University
of Idaho studies).
Simply stated, biodiesel used in a mixture
at or above 2% is beneficial for the long term wear protection
of diesel fuel engines.
Lubricity Properties
For many years, the lubricity of diesel
fuel was sufficient to provide the protection needed to maintain
adequate performance. Recent changes (1993 and beyond) in the
composition of diesel fuel, primarily the need to reduce fuel
sulfur and aromatic levels, and the common chemical process used
to accomplish these changes (called hydro-treating) have inadvertently
caused the removal of some of the compounds that provide lubricity
to the fuel. According to Mr. Paul Henderson, Quality Management
Systems Manager for Stanadyne Automotive Corp. (the leading independent
US manufacturer of diesel fuel injection equipment) in comments
provided to the Chairman of the Kansas House Environment Committee
March 8, 2000:
"There have been numerous examples from
the field where lack of
lubricity in the fuel has caused premature equipment breakdowns
and in some cases, catastrophic failures. This problem will be
more dramatic as EPA moves to further reduce the sulfur levels
in petrodiesel fuel."
A 1998 review paper on fuel lubricity worldwide
showed that diesel fuel in the US and Canada is some of the poorest
lubricity fuel found in the entire world Of the 27 countries surveyed,
only Canada, Switzerland, Poland and Taiwan had poorer lubricity
fuel than the US. With a mean fuel lubricity of just under the
recommended specification of an HFRR (High Frequency Reciprocating
Rig) wear scar diameter of 460 microns. In the US, 50% of the
fuel was found to be worse (>460 micron scare) than that recommended
by equipment manufacturers. The severe hydrotreating required to reduce fuel sulfur
to lower sulfur content specifications will cause a further reduction
in fuel lubricity compared to today's diesel fuel, and is of concern
to engine and fuel injection equipment manufacturers.
The Fuel Injection Equipment (FIE) manufacturers
have adopted the use of the HFRR (ISO 12156-2:1998), and recommend
that all diesel fuel meet a limit of 460 micron maximum Wear Scar
Diameter (WSD)3. For the HFRR, a lower wear scar indicates better
lubricity.
Biodiesel has been tested , at varying concentrations,
with poor lubricity Number 2 and Number 1 diesel fuels representative
of that on the market after 1993 (i.e. fuel refined to meet a
500 ppm maximum sulfur content). The results are illustrated in
the table below.
|
Percent Biodiesel |
HFFR Scar (mm)* |
| |
Diesel Number2 |
Diesel Number1 |
|
0.0 |
536 |
671 |
|
0.4 |
481 |
649 |
|
1.0 |
321 |
500 |
|
2.0 |
322 |
355 |
|
20.0 |
314 |
318 |
|
100.0 |
314 |
314 |
*Results provided by Stanadyne Automotive
Corp.
Based on the HFRR testing run by Stanadyne,
and testing from other laboratories showing similar results, Stanadyne
Automotive has stated:
"….we have tested biodiesel at
Stanadyne and results indicate that the inclusion of 2% biodiesel
into any conventional diesel fuel will be sufficient to address
the lubricity concerns that we have with these existing diesel
fuels. From our standpoint, inclusion of biodiesel is desirable
for two reasons. First it would eliminate the inherent variability
associated with the use of other additives and whether sufficient
additive was used to make the fuel fully lubricious. Second,
we consider biodiesel a fuel or fuel component-not an additive…Thus
if more biodiesel is added than required to increase lubricity,
there will not be the adverse consequences that might be seen
if other lubricity additives are dosed at too high a rate."
Simply stated, biodiesel used in a mixture
at or above 2% is beneficial for the long term wear protection
of diesel fuel engines.
Biodiesel
Compared to BluDiesel® (Agip), Ecoplus® (Tamoil), E-Energy® (Environmental Diesel; Esso),
HiQ® (Q8), V-power® (Shell)
In Europe, a new products are marketed by various petroleum
companies (Agip of Eni, Tamoil, Esso of Exon Mobile, Q8 and Shell).
These "no sulfur*"diesel fuels, are available at the
aforementioned fuel stations and normally costs 3-5 euro
cents more than regular diesel. The "no sulfur*" content
of these fuels is actually a stated value not to exceed 10ppm. Further,
BluDiesel® boasts a maximum wear scar value of 460 microns
(387 microns for the test batch of BluDiesel). Although the tests
for lubricity properties of biodiesel and BluDiesel® were
not performed "side-by-side", if biodiesel were added
to these products at between 2 and 20%, the wear scar values would
be less than 320 microns. While not claiming that biodiesel is
a superior fuel over the above products, it is apparent that biodiesel
could improve the engine protection properties of petroleum based diesel
while further reducing the concentration of sulfur (biodiesel
contains NO sulfur).
Power
Differences
Studies conducted in the U.S. and Europe
generally indicate that blends of Biodiesel and petrodiesel result
in small decreases in overall power output of engines. Only two
studies have been conducted with marine engines, one by a German
scientist (Dr. Claus Breuer) at the Technical University in Hannover
(Ph.D. thesis in 1994) and the other by Alvin Womac's group at
the Department of Agricultural Engineering at the University of
Tennessee. The German study involved a Deutz 4 cylinder marine
diesel engine (direct injection) found on fishing boats in Europe
and the Tennessee study evaluated a 110 HP Volvo marine diesel
engine, also used in work boats and fishing boats. Volvo also
makes smaller single and double cylinder diesel engines for recreational
sailboats.
The German study confirmed similar results obtained by Mercedes
Benz showing that the maximal torque curve for an engine under
load remains essentially unchanged for rapeseed methyl esters
relative to pure petrodiesel. Despite the lower volumetric heating
value and the consequent lower maximum power output of Biodiesel,
the practical results are roughly the same. At a 20% blend, there
would probably be no noticeable difference in power output. Good
performance in fuel combustion with Biodiesel and its blends resulted
in a smooth running engine.
In the Volvo marine diesel engine study in Tennessee (110-HP,
2.39 L, 4-cylinder, direct injection engine), a tractor dynamometer
was used to measure power outputs under selected loads through
an engine-mounted reverse drive gear. Exhaust emissions were also
tested along with fuel consumption tests under various loads.
The conclusions of these tests were that power produced from 100%
soy methyl ester Biodiesel was from 2 to 7 percent less than produced
from petrodiesel, depending on the load-speed point. However,
at or near maximum throttle (3,800 rpm), the two fuels performed
the same. Interestingly, at the lowest engine speed (1855 rpm)
at full throttle under heavier load, there was a 13% increase
in power with Biodiesel as compared to petrodiesel.
The Tennessee study indicated that using 100% Biodiesel in marine
direct-injection diesel engines, with design and construction
similar to the Volvo test engine, could be recommended without
any significant, noticeable differences in operation, power performance
and fuel usage.
In the 1998 study at the Southwest Research Institute on Biodiesel
effects on diesel engine performance, engine power in the 1997
Cummings truck engine operating on the B-20 blend was at 98.5%
of the power attained with low sulfur No. 2 diesel. At 100% Biodiesel,
the engine generated 92% of the power. For a Detroit Diesel truck
engine (1997), the power was 98% with the B-20 and 92% with the
neat Biodiesel.
Fuel Consumption
Differences
Biodiesels are mono-alkyl esters containing approximately 10%
oxygen by weight. The oxygen improves the efficiency of combustion,
but it takes up space in the blend and therefore slightly increases
the apparent fuel consumption rate observed while operating an
engine with Biodiesel. In the Southwest Research Institute study
(1996), the fuel consumption was found to increase by only 2%
for a B-20 blend with methyl esters, and by 14% when methyl ester
Biodiesel was used at 100% in the Cummins test engine operated
under transient heavy loads. The brake-specific fuel consumption
was 0.43 lb./HP-Hr for regular petrodiesel no. 2, 0.44 lb./HP-Hr
for the B-20 blend, and was 0.50 lb./HP-Hr for the neat RME Biodiesel.
In testing Biodiesel in the CytoCulture Mercedes Benz diesel station
wagon over the past 4 years, there was about a 15% net decline
in the mileage obtained using neat Biodiesel vs. petrodiesel.
No change in power, acceleration or engine temperature was observed,
but the engine was quieter and smoother at idle when fueled with
Biodiesel. At a 20% blend with petroleum diesel, the fuel consumption
differences are practically unnoticeable.
These local observations were confirmed by the 1998 engine performance
studies at the Southwest Research Institute. Fuel consumption
in a 1995 Cummings B-5.9 truck engine increased by 9% with the
B-20 blend, and by 18% with the neat Biodiesel. Better fuel economy
was noted for a 1997 Cummings N-14 truck engine with a 3% drop
in fuel consumption using B-20 and a 13% increase with the neat
Biodiesel.