At the University
of Tennessee at Knoxville, a diesel car spins its wheels on a treadmill
called a chassis dynamometer. It looks like a patient having heart surgery.
It is highly instrumented to provide on-line measurements of its engine's
speed, power, and fuel use and the ability of its exhaust treatment
system to remove harmful constituents.
ORNL's Engineering Technology Division (ETD) take measurements on this
car, as well as on engines at the four stationary engine dynamometers
at DOE's Advanced Propulsion Technology Center (APTC). These dynamometers
will eventually be moved from this user facility at ORNL to the National
Transportation Research Center, which will also acquire chassis dynamometers.
ORNL research on these machines is guiding the development of effective
emissions control systems for next-generation vehicles.
The heart of the
lean, clean car of the future proposed by the U.S. Partnership for a
New Generation of Vehicles (PNGV) is likely to be a compression-ignition,
direct-injection diesel engine that uses 40% less fuel per mile than
do today's typical gasoline-burning cars. If the diesel engine is combined
with an electric motor in a hybrid car, it could come close to meeting
the PNGV goal of 80 miles per gallon for a family-sized sedan.
the lean-burn operation of diesel engines is incompatible with today's
catalytic converters used to eliminate 90% of the nitrogen oxides (NOx)
in gasoline car exhaust. In addition to producing NOx, which
contributes to acid rain and smog (which, in turn, creates a greenhouse
effect), diesel engines also emit particulate matter-airborne soot particles
that may be hazardous to humans inhaling them because they are small
enough to reach the lungs. To meet PNGV goals and the tough emissions
standards mandated for 2006 by the Environmental Protection Agency (EPA),
new exhaust treatment systems are being developed for diesel engines
by catalyst companies and DOE national laboratories. The APTC, led by
Ron Graves, Ralph McGill, and others in ETD, is playing a key role in
evaluating these emissions control systems to help improve their effectiveness.
"We use an engine
dynamometer to determine how well the engine, fuel system, and emissions
control system work together," McGill says. "We measure the engine's
speed and load, the fuel system's air-fuel ratio, and the concentration
of constituents in the exhaust before and after treatment by the emissions
control system. We are trying to determine and optimize the efficiency
of the catalytic converter in reducing emissions."
West checks a Mercedes A170 diesel engine, which is being tested
to determine the efficiency of its emissions control system in
removing nitrogen oxides and particulate matter from its exhaust.
The engine is run on an ORNL stationary engine dynamometer, which
applies the same resistance to the engine as the road would if
the engine were connected to wheels. (Top photo enhanced by Gail
"We are now conducting
dynamometer experiments on seven enginesone gasoline and six diesel
engines, plus two vehicles," Graves says. "This effort demonstrates
the high level of interest in the diesel engine today and the challenge
of solving the emissions problems with those engines." The ETD researchers
are working with auto makers and diesel engine manufacturers through
seven cooperative research and development agreements. Important results
have emerged from these collaborations.
"We have developed
methods and instruments to measure faster and more accurately the concentrations
of a broad range of exhaust constituents," says Graves. "These constituents
include nitrogen oxides, particulate matter, sulfur oxides, carbon monoxide,
"We showed that
advanced diesel vehicles could achieve 2006 emissions standards. We
did some clever engineering to create a highly effective emissions control
strategy for a diesel car. We determined the right mixture of hydrogen
and carbon monoxide from unburned diesel fuel that could regenerate
the NOx adsorber and simulated this exhaust mixture with bottled gas.
This mixture is injected at precise intervals and reacts with the nitrogen
oxides, converting them to nitrogen, carbon dioxide, and water vapor."
Partridge prepares to use a mass spectrometer to analyze the effectiveness
of diesel fuel hydrocarbons in regenerating a catalyst used to
remove nitrogen oxides from engine emissions. (Photo
by Curtis Boles and enhanced by LeJean Hardin.)
John Storey and
others in ETD developed an electrostatic method of capturing diesel
particulates from engine exhaust so their structure and makeup can be
studied. Doug Blom in the Metals and Ceramics Division is studying these
samples of particulate matter using the Hitachi HF-2000 transmission
electron microscope. He has found that the structure of these particles
ranges from noncrystalline to semicrystallinethe atoms are lined
up in layers that are oriented in different directions. Pete Reilly
of ORNL's Chemical and Analytical Sciences Division has developed a
laser-based ion trap mass spectrometer that can be used to determine
the composition of particles measuring 1 to 100 nanometers in real time.
"If the particles
we measure are mostly sulfuric acid, then we must rethink whether they
represent a health risk or are harmlessly diluted by water in the lungs,"
Graves says. "If they are a health problem, it could go away after fuel
sulfur is lowered to meet EPA limits." (See An
Emissions Mission: Solving the Sulfur Problem.) More precise
information on the makeup of particulate matter could steer scientists
to a better understanding of its health effects.
this computational visualization by ORNL's Engineering Technology
and Computer Science and Mathematics divisions (courtesy of Ross
Toedte), the temperature contours and flow streamlines represent
the combined effects of exhaust gas flow, heat transport, and
chemical reactions in a typical automotive catalytic converter
during a cold start. Cold start performance is critical to reducing
harmful emissions from automobiles.
Advanced Propulsion Technology Center
Chemical and Analytical Sciences Division
Engineering Technology Division
Metals and Ceramics Division
for a New Generation of Vehicles