To reduce the use of imported oil for transportation and improve air quality, ORNL and UT researchers are conducting research that supports the design of cars and trucks that use fuel more efficiently
Inefficient vehicle exhaust.
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Since the 1970s the U.S. government has supported research and development designed to help Americans use energy more efficiently. Because a large portion of American oil imports is used for transportation, the Department of Energy makes substantial investments at ORNL in several technologies designed both to improve fuel efficiency and reduce carbon emissions into the atmosphere.
The concept is simple in theory. In the near term, having an affordable supply of fuel requires that the next generation of cars and trucks burns fuel far more efficiently than these vehicles do today.In the long term, vehicles should burn a non-petroleum fuel, such as hydrogen (see Multiple Roads to the Hydrogen Car). In addition to the economic and strategic benefits of a sustained domestic energy supply, these changes would be accompanied by reduced emissions of health-threatening air pollutants. Finally, efficient vehicles of the future should be made out of materials that are lighter than steel but at least as strong and stiff, to protect passengers during collisions.
Researchers with ORNL and with the National Transportation Research Center (NTRC) are working to help the transportation industry move toward these goals. Says NTRC Director Ed Grostick, "Our researchers are focused on practical technologies that are ready to be applied in the manufacture of new vehicles."
NTRC includes research staff from both ORNL and the University of Tennessee. A large portion of the research at the NTRC and ORNL is funded by DOE's Office of FreedomCAR and Vehicle Technologies.
Fuels and Engines
NTRC researchers are developing and applying new diagnostic tools and control strategies to help American automakers and engine companies improve the efficiency of internal combustion engines (ICEs), while simultaneously reducing their harmful exhaust emissions to levels so low they are difficult to measure. Because modern diesel engines are 30 to 50% more efficient than gasoline engines in cars and light trucks, NTRC researchers have set their sights on drastically reducing the emissions of nitrogen oxides (NOx) and particulate matter, which threaten respiratory health, so the vehicles will meet federal environmental standards and become more acceptable to American consumers.
Toyota Prius hybrid car engine.
For several years NTRC's Fuels, Engines, and Emissions Research Center (FEERC), led by Johney Green and Ron Graves, has focused research on emissions controls and catalyst-based after-treatment technologies for exhaust from diesel engines. Two unique FEERC inventions, the SpaciMS and a phosphor thermography instrument, were used together to map the dynamic, subtle changes in the chemical composition and temperature of emissions passing through a catalyst.
By combining FEERC's diagnostic tools with state-of-the-art electronic engine controls, the center's researchers are elucidating the interactions of exhaust species and the operation of lean-NOx traps, a leading technology for controlling diesel emissions.
"In normal lean engine operation, lean NOx traps store NOx," Graves says. "A rich engine cycle supplies hydrocarbons in the exhaust that react with the NOx on a catalyst to reduce it to nitrogen and other harmless byproducts. Controlling a diesel engine system so that it enters a rich regime without a driver noticing, while ensuring the generation of the right exhaust conditions for the NOx trap, are tremendous challenges."
FEERC provided the first publicly available information on ways to operate diesel engines in low-temperature combustion modes that exhibit low NOx and soot emissions simultaneously. Fully detailed emissions data, plus ways to maintain fuel economy in these low-temperature modes, are among FEERC's special contributions. The center has joined with industry in motivating the preparation of improved computational tools to simulate the operation of lean-burning engines and their emission control systems.
Power Electronics and Motors
Each of the three U.S. automakers plans eventually to manufacture hybrid gasoline-electric cars that are competitive with early models on the road today. According to Don Adams, director of NTRC's Power Electronics and Electric Machinery Research Center, ORNL researchers are developing power electronics and electric motors that could help U.S. automakers produce a less expensive, better performing, more reliable hybrid car.
ORNL researchers have helped develop or improve new types of electric motors that are simpler to control, lighter, and more powerful than those currently used in Japanese hybrid vehicles. All electric motors require some type of electronic drive, or inverter, to allow them to run at different speeds and power with the electricity generated by the engine or by braking. ORNL has teamed with industry to improve the inverter, enhancing its reliability and shrinking it from the size of a telephone booth to that of a telephone book.
ORNL research focuses on finding ways both to fabricate electronic devices that can withstand higher temperatures and to cool these devices more effectively. New materials becoming available, such as silicon carbide, can withstand much higher temperatures and be switched on and off faster, enabling better control of electric motors. If all the components in an inverter can be made to run at these higher temperatures, or if a better technique could be developed to spray a fluid on silicon devices and motors to cool them, then the hybrid car's cooling system could be decreased in size. The result would be a lighter vehicle and increased performance.
ORNL researchers are also working on developing smaller, lighter, and cheaper batteries and capacitors for storing more of the hybrid vehicle's electrical energy for longer times. All of this research could lead to a more affordable hybrid car.
More with Less
Making cars and trucks lighter is another important way to reduce fuel consumption. Phil Sklad, ORNL's technical program manager for both DOE's Automotive Lightweighting Materials and High Strength Weight Reduction Materials Technology Development areas, says the programs seek to identify materials and materials-processing technologies that can reduce vehicle weight.
One DOE goal is to reduce a five-passenger car's weight by half by 2010, maintain affordability, and increase the use of recyclable and renewable materials. Another DOE goal is to reduce the weight of trucks to increase fuel use efficiency. "If the weight of a heavy truck is reduced using lighter but stronger materials, the truck can carry more freight," Sklad says. "A fully loaded truck cannot legally weigh more than 80,000 pounds. If trucks are made lighter, they can carry more payload. Thus, 9 trucks instead of 10 could legally carry the same total payload with a substantial reduction in fuel use."
Over the years, heavy steel has been the dominant structural material in vehicle frames and other components. The automotive industry is already replacing some parts made of regular steel with parts fabricated from aluminum, magnesium, glass composites, carbon-fiber composites, and advanced high-strength steel. The newer steel is tailored to promote a microstructure that gives elevated properties, allowing the use of thinner, lighter sheets of the material for automotive structures.
The program Sklad heads has found that each material has both advantages and drawbacks. "If you replace the steel in a car with carbon-fiber composites, you reduce the vehicle's weight by about two-thirds," Sklad says. "But cost remains a barrier. The automotive industry will not replace steel with carbon fiber until the cost of the fiber is reduced to $3 to $5 a pound."
ORNL researchers Alicia Compere and Bill Griffith, along with their collaborators at UT and North Carolina State University, are pursuing a way to make carbon fiber for less than $5 a pound, a dramatic drop from the $8 a pound cost of commercially produced carbon fiber made using petrochemicals. The ORNL-university technology is based on producing fibers in a size range suitable for automotive and aerospace composites by "melt-spinning" them from a blend of pulp-mill lignin—a waste product of the paper industry—and recycled plastic.
Carbon-fiber composites have been "crushed" at NTRC's Test Machine for Automotive Crashworthiness (TMAC). The energy absorption properties of composites and metals are measured in TMAC. These measurements are entered into supercomputer models that simulate collisions, aiding in the design of safer lightweight vehicles in which both stiffness and strength are taken into account.
The work is slow and methodical, but researchers continue to keep the goal in sight, knowing the answers may someday be an important contribution to the world's energy needs.
The Department of Energy's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time.