Ill. – In the first use ever of a new three-dimensional
technique to study diesel engine emissions, researchers
at the U.S. Department of Energy's Argonne National
Laboratory developed information that could lead to
improved exhaust-cleaning devices, ways for industry
to meet environmental regulations, and new insights
on the impact to public health from diesel engine
Engineers at Argonne's Center for Transportation Research
determined that emission particles are not spheres,
as is usually assumed, and that shape varies depending
on engine speed and load.
Emissions from diesel engines are of concern because,
like their gasoline counterparts, they contain nitrogen
oxides – NOx – that contribute to smog and global
warming. Also like gasoline engines, diesel engines
produce exhaust that contains nano-sized particles,
which can be inhaled and might cause health problems.
Diesels are the most efficient heat engines ever built.
They are highly durable and 30 to 40 percent more
fuel efficient than gasoline engines. Though not currently
popular with U.S. auto buyers, diesels power trucks,
trains and construction equipment in this country.
“Throughout Europe and the rest of the world, diesels
are popular,” explained mechanical engineer Raj Sekar,
who leads the Engine and Emissions Research Group
doing the research. “As the cost of fuel increases,
diesel cars will look more attractive. If you have
to pay $3 a gallon to fill your car, wouldn't you
rather get 40 percent better fuel economy?”
Sekar's group studies in-cylinder combustion on engines
ranging from cars to locomotives. Using the dynamometer
at Argonne's Engine Research Facility to operate the
engines from idling to full load, engineers ran tests
on a Mercedes 1.7 liter automotive diesel – commonly
used in passenger cars in Europe – and a 2.4 liter
single-cylinder version of Caterpillar truck diesel
using pump-grade fuel.
Argonne mechanical engineers Kyeong Lee and Jerry
Zhu, developed a bench-scale thermophoretic sampling
technique to work on internal combustion engines.
His work revealed the form and structures of diesel
engine particulates in three dimensions for the first
Emission samples were collected at two-foot-intervals
along a nine-foot-long exhaust pipe. The exhaust temperatures
ranged from 1,200 degrees Fahrenheit (650 degrees
Celsius) near the engine to 200 degrees F (90 degrees
C) at the tailpipe. Lee analyzed the samples in the
transmission electron microscope at Argonne's Electron
Microscopy Center at 250,000 times magnification to
reveal particle shape, form and microstructure. A
spectroscope associated with the microscope revealed
that the particulate matter is about 95 percent carbon,
with smaller concentrations of oxygen, silicon and
sulfur. “These chemicals may come mostly from fuel
or lubrication oil,” Sekar said.
“Small particles come out from the engine, but as
they travel down the exhaust pipe and they start to
cool, the particles attach to one another and may
also chemically react,” Sekar said. “What comes out
of the engine may not necessarily be what comes out
of the tailpipe, so this testing allows us to track
particle transformation to understand what gets into
“We hope that these results will guide the design
of an advanced particulate trap or other mitigation
devices,” said Sekar. “We are also creating a database
that will be used to study the health effects of emissions.”
Previous tests have been simpler and mainly quantitative.
For example, the Environmental Protection Agency standards
are based on simple mass analyses. Exhaust is collected
on filter paper and weighed to determine how much
particulate matter is emitted.
Lee determined that temperature is the most sensitive
parameter for particulate formation and destruction.
The higher temperatures caused by carrying higher
loads – 2,500 revolutions per minute at 100 percent
load – reduced the primary particle sizes and produced
significant oxidation, or combustion. He also found
a broad size distribution of particles at various
engine speeds and loads.
Particulate from the truck engine was more compact;
particulate from the car engine was more chain-like.
Researchers also used an Argonne-patented technique
called laser-induced incandescence on the engines,
in addition to many commercial instruments. This technique
provides real-time information about the instantaneous
mass, size and number of particles per liter of exhaust
gas, even as engine operating conditions change.
Engineers are currently studying a gasoline-powered
car engine for comparison. “Both diesel and gasoline
engines,” Sekar said, “produce the greenhouse gas
carbon dioxide, but since diesel is 30 to 40 percent
more efficient, it produces 30 to 40 percent less
carbon dioxide. And so many more cars are powered
by gasoline in this country.”
Future research plans include investigating the relationship
between engine operation and particulate formation
and oxidation, examining particulate microstructure
and exploring the impact of fuel properties on diesel
Argonne engineers worked with research partners at
the University of Illinois at Chicago, Drexel University,
the Korea Advanced Institute of Science and Technology,
Brown University and the National Institute of Standards
Funding was provided by the FreedomCAR &Vehicles
Technology Program in the DOE's Energy Efficiency
and Renewable Energy Program.
The nation’s first national laboratory, Argonne National
Laboratory conducts basic and applied scientific research
across a wide spectrum of disciplines, ranging from
high-energy physics to climatology and biotechnology.
Since 1990, Argonne has worked with more than 600
companies and numerous federal agencies and other
organizations to help advance America's scientific
leadership and prepare the nation for the future.
Argonne is operated by the University of Chicago for
the U.S. Department of Energy's Office of Science.