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New Tank Innovation Makes Small Natural Gas Vehicles Attractive


March 9, 2007


Technology uses corncobs to create space-saving briquettes for
low-pressure tanks. A development in natural gas technology will make it
possible to create a space-saving low-pressure tank that could
revolutionize the capacity of natural gas to power vehicles, especially
smaller cars.

The innovation is the result of a partnership between researchers at the
University of Missouri-Columbia (MU) and the Midwest Research Institute
(MRI). The team is testing the technology in a pickup truck owned and
operated by the Kansas City (Mo.) Office of Environmental Quality.

“Natural gas is a promising fuel because it’s clean-burning, and most of
it can be produced domestically in the U.S.,” said Peter Pfeifer, MU
professor of physics and principal project leader. “Our new technology
makes it possible to move natural gas forward as the potential fuel of the
future.”

Current natural gas vehicles use bulky high-pressure tanks that must be
cylindrical in shape and take up a small car’s premium cargo space, such
as the trunk. The MRI-MU team’s innovation makes it possible to store
natural gas in a smaller, low-pressure tank that can be made in
rectangular form and mounted under a car’s floor. Making this possible is
an MU discovery that fractal pore spaces (spaces created by repetition of
similar patterns at different levels of magnification) are remarkably
efficient at storing natural gas.

Researchers have developed a way to “bake” ground corncobs into carbon
briquettes that contain these fractal pore spaces. The walls of the
nanoporous carbon adsorb methane molecules as a high-density fluid, and
the strong attractive force in the narrow pores lowers the energy of the
molecules so that they can be packed more closely than in the absence of
the carbon. This makes it possible to create a low-pressure natural gas
tank.

“The research partnership here exemplifies how scientists from very
different fields can work together to conduct truly fundamental research
in new materials with the explicit goal of having the results of the
research solve problems for people,” said MU Chancellor Brady Deaton.

Pfeifer said the MRI-MU tank reaches the U.S. Department of Energy’s (DOE)
target for the first time. The briquettes can store 180 times their own
volume of natural gas, or 118 grams of methane per liter of carbon, at 500
pounds per square inch (35 atmospheres); the best previous carbon could
only store 142 times its own volume at 500 psi pressure.

“We hope that this will lead to the design of low-pressure tanks that will
solve the cargo space problem posed by high-pressure tanks,” Pfeifer said.

The pickup truck fitted with a prototype tank has been on the road since
mid-October. Researchers are collecting data to evaluate the mileage per
fill-up, pressure and temperature of the tank during charging/discharging;
charging/discharging rates under various fueling/driving conditions; and
longevity of the carbon briquettes.

“Having a prototype of this technology operating in the day-to-day work
environment is significant,” said James L. Spigarelli, president and CEO
of Midwest Research Institute. “Although the team’s work is not yet
complete, this technology development comes at a fortuitous time as many
researchers strive to find multiple alternatives to address the nation’s
energy challenges.”

According to a DOE publication, using natural gas instead of traditional
fuels results in a reduction of carbon monoxide and nitrogen oxides,
smog-producing gases, by more than 90 percent and 60 percent,
respectively, in light-duty applications. Carbon dioxide, a greenhouse
gas, is reduced by 30 to 40 percent. Compared to commercial diesel engines
in medium- and heavy-duty applications, natural gas engines can reduce
carbon monoxide and particulate matter by more than 90 percent and
nitrogen oxides by more than 50 percent. Also according to DOE
publications, only 15 percent of the natural gas used in the U.S. in 2004
was imported, and most imports came from Canada.

Natural gas is cheaper than gasoline and diesel on an energy-equivalent
basis, Pfeifer said. In June 2006, the national average cost of compressed
natural gas was 94 cents cheaper than gasoline on an energy-equivalent
basis, according to the Clean Cities Alternative Fuel Price Report.

This project was funded by a $600,000 grant from the National Science
Foundation’s program Partnerships for Innovation. Additional funds
totaling more than $400,000 came from MU, MRI, the U.S. Department of
Energy and the U.S. Department of Education.

 

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