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Researchers at Argonne have begun to investigate adding one more contender to the list of possible energy sources for light-duty cars and trucks: Compressed natural gas (CNG). Image: Mercedes Benz
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As the United States
transitions away from a primarily petroleum-based transportation industry, a
number of different alternative fuel sources—ethanol, biodiesel, electricity,
and hydrogen—have each shown their own promise. Hoping to expand the pool even
further, researchers at the U.S. Department of Energy's Argonne National
Laboratory have begun to investigate adding one more contender to the list of
possible energy sources for light-duty cars and trucks: Compressed natural gas
(CNG).
Compressed
natural gas is composed primarily of methane, which when compressed occupies
less than one percent of the volume it occupies at standard pressure. CNG is
typically stored in cylindrical tanks that would be carried onboard the
vehicles it fuels.
Because
the domestic production of natural gas has increased dramatically over the past
ten years, making a large number of the cars and light trucks currently on the
road CNG-compatible would help to improve U.S. energy security. "As a
country, we don't lack for natural gas deposits," said Argonne
mechanical engineer Thomas Wallner. "There are fewer obvious challenges
with direct supply than with most other fuels."
Natural
gas currently comes primarily from deep underground rock structures, including
shale. Recent improvements with hydraulic fracturing, or "fracking,"
a controversial process that some critics claim can hurt the environment, have
made it economical for natural gas companies to extract a greater supply of
natural gas from unconventional sources.
Like gasoline,
both the production and combustion of CNG release greenhouse gases into the
atmosphere. To be able to make an accurate comparison to gasoline, scientists
and engineers will need to look at each stage of the fuel's production and use,
said Argonne environmental scientist Andrew
Burnham.
Unlike
gasoline, however, CNG markets are relatively insulated from geopolitical
shocks, said Wallner. "The price of CNG has been and will probably
continue to be both cheaper and more stable over the long term than
gasoline," he said.
CNG
currently costs the equivalent of about $2 per gallon, roughly half that of
current gasoline prices, according to Wallner.
In order
for CNG to take hold, many more stations will need to offer it as an option,
and the infrastructure for delivering and distributing the fuel around the
country will have to be built up. There are currently fewer than 1,000
publically available CNG refueling stations in the United States, in comparison to
nearly 200,000 gas stations.
Argonne already has the capability to help
automotive industry leaders test and analyze CNG vehicles. In particular,
Argonne's Greenhouse Gases, Regulated Emissions, and Energy Use in
Transportation Model gives experts the ability to examine the greenhouse gas
emissions of various fuels from "well-to-wheels," involving each
stage of production, distribution, and combustion. "We have years of
expertise working with industry to develop alternative-fuel vehicles as well as
the tools necessary for the public to understand the impact of these vehicles
on the environment," said Argonne mechanical engineer Michael Duoba.
Although
CNG vehicles emit fewer greenhouse gases than conventional automobiles as fuel
is combusted, "upstream" challenges in production and distribution of
CNG—particularly methane leakage—make it somewhat less attractive when it comes
to preventing climate change. "There are a lot of points in the life-cycle
of the fuel where we still need better data," Burnham said. "There
are technological opportunities for us to capture the leaked natural gas and reduce
greenhouse gas impacts."
For
heavy-duty applications, like city buses, CNG might have the potential to cut
down emissions of particulate matter and nitrogen oxides, helping municipalities
to meet more stringent EPA standards enacted in the past few years, according
to Burnham.
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