The California Air Resources Board is conducting a comprehensive study to better characterize
the potential emissions benefits of CARB ULSD compared to other federal diesel fuels. The goal
of this study is to understand the impacts of emissions from these different fuels in diesel engines.
The program includes engine dynamometer and chassis dynamometer emissions testing with
three different fuels. The testing included a baseline CARB ultralow sulfur diesel (ULSD) fuel
and two federal diesel fuels. One Federal fuel, referred to as “Federal A”, represents an average
Federal ultralow sulfur diesel fuel and the second, referred to as “Federal B”, is commercially
available Federal ultralow sulfur diesel fuel that due to its properties may contribute to higher
exhaust emissions. This memorandum summarizes the results from three engines tested under
this comprehensive program. The testing described in this memorandum was conducted on a
2007 MBE4000 engine, a 2006 Cummins ISM engine and a 1991 Detroit Diesel Series 60 engine
in CE-CERT’s engine dynamometer laboratory. Testing was also conducted on two different
engine test cycles, the FTP and 50 mph CARB cruise cycles.
A summary of the results is as follows:
Engine Testing Results:
• NOx emissions for the Federal A and Federal B fuels were higher than those for the
CARB ULSD for all the engines and cycles. The NOx increases compared to CARB for
the different engines ranged from 4.7 to 10% for the two Federal fuels, were statistically
significant for all cases, and were similar between the different test engines. For the 2006
Cummins and the 1991 DDC 60 engines, the emissions for the Federal B fuel were higher
than those for the Federal A fuel for most cycle combinations. For 2007 MBE 4000 and
1991 DDC 60, the observed emissions impacts were greater for the FTP than the 50 mph
cruise. The opposite trend was seen for the Federal A fuel for 2006 Cummins engine with
respect to cycle differences, although this is probably due in part with some stability
issues that were seen during the testing for the 50 mph cruise cycle for the Cummins
engine.
• The PM emissions showed statistically significant increases on the Federal A and B fuels
for the Cummins engine over the FTP, but not over the 50 mph cruise cycle or for the
MBE4000 on either cycle. For the MBE4000, the values are very low, so the differences
were within the measurement error at these levels.
• THC emissions on 1991 DDC 60 showed statistically significant differences between
fuels ranging from a 14.4-29.5% increase using Federal diesel blend fuels, while no
consistent trends between different fuels for MBE4000 and 2006 Cummins ISM were
observed for the 50-mph cruise cycle.
• CO Emissions for all the three engines showed higher emissions for both Federal diesel
blends compared with CARB diesel. The CO emissions increases were highest for the
FTP cycle for all the three engines. The emissions differences between CARB diesel and
the Federal diesels for the 2006 Cummins and the 1991 DDC 60 varied from
approximately 3 to 23%.
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• CO2 emissions showed slightly higher emissions for both Federal diesel blends and all
three engines. The CO2 emissions increases were relatively consistent between the three
engines and ranged from 1-2%, with the Federal B fuel showing slightly higher increases
than the Federal A fuel on the Cummins and DDC 60 engines for the 50 mph cruise
cycle.
• Some trends of lower brake specific fuel consumption were seen for the Federal B fuel.
The differences between Federal B and CARB ULSD over the FTP cycle for all three
engines were statistically significant. For 1991 DDC 60 the differences between the
CARB ULSD and Federal B were also statistically significant over the 50 mph cruise.
The lower fuel consumption for the Federal B fuel is not unexpected, given that this fuel
has a higher density than the other test fuels. The CARB and Federal A fuels did not
show any differences in fuel consumption for the Cummins engine.
