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Jury Still Out on NGV Carbon Footprint, Says Carnegie Mellon

While coalition-backed research on natural gas vehicle (NGV) methane emissions is ongoing at the University of West Virginia (see Daily GPI,  Sept. 14), a Carnegie Mellon University (CMU) study of potential greenhouse gas (GHG) emissions from NGVs has some troubling findings.

Researchers at CMU's Fuels Institute found that the greatest GHG emissions benefit in the alternative transportation fuel sector is battery electric vehicles charged with electricity coming solely from advanced combined-cycle gas-fired generation. Hydrogen fuel cells and compressed natural gas (CNG) vehicles "were found to have comparable life-cycle emissions with conventional gasoline," according to the report.

But the researchers acknowledged that the "uncertainty and variability in life-cycle GHG emissions of natural gas pathways must be taken into consideration when contemplating the implications of such studies," a CMU spokesperson said.

John Eichberger, executive director of the Fuels Institute, cautioned that "an accurate evaluation of the environmental effects of any fuel, including natural gas, requires a comprehensive assessment," while adding that he thinks the CMU report is a "valuable addition to the information available and will help advance our efforts to understand the role natural gas may play in the transportation sector."

The report is the second in a series of studies by the CMU institute and the National Association of Truck Stop Operators (NATSO) Foundation. The studies are spurred by the "low-cost and abundant supply of shale gas in the United States," according to the CMU spokesperson.

"Additional work in this series will look at the potential for natural gas-based fuels to reduce other air pollutants and what effect such fuels might have on consumers, specifically related to cost, performance, convenience and safety."

Eichberger said CMU also is looking at the feasibility of developing an infrastructure system to support a natural gas transportation economy. CMU's initial report was recently published in the journal Environmental Science and Technology, and added perspectives on the report are available on the CMU institute's website.

Separately, as one of 16 separate studies -- not all national -- the Environmental Defense Fund, along with industry, think tank and university collaboration, enlisted the University of West Virginia's Center for Alternative Fuels, Engines and Emissions, and the International Council on Clean Transportation to quantify the volumes of methane emissions attributable to NGV fleets and passenger cars operating on CNG and liquefied natural gas. The study is due to be released by early next year.

Meanwhile, Cenergy Solutions has opened a test center in Fremont, CA, for the adsorbent natural gas technology (ANG), reviewing a patent-pending dielectic gas desorption design, which is bidding for commercialization. Earlier this year, Cenergy COO Gary Fanger said he hoped to be marketing the fueling system to fleets and some consumer markets by the end of this year (see Daily GPI,  April 17).

Fanger said the technology would permit fleet operators and others to fill their NGVs at pressures under 500 psi and get ranges similar to that available from today's 3,600-psi CNG fuelings.

The technology is applicable to existing CNG cylinders, according to reports in the sector newsletter Fleets & Fuels, and it may also be applied to 350-500 psi containers that are lighter and can be designed to fit in various areas of empty space on vehicles.

Portland, OR-based NW Natural is testing Cenergy's first generation ANG system, along with The Gas Connection in Denver and AAAA Generator in California. A NW Natural engineer involved in the tests said ANG allows more CH4 molecules in the gas to readily adhere to the surface of tanks, and that increases the number of molecules that ultimately can be contained in the tank.

Also in California, a Greenkraft truck modified by Efficient Drivetrains Inc. (EDI) unveiled a CNG-fueled plug-in hybrid electric Class 4 logistics truck. The vehicle includes EDI's drive train technology and vehicle control software.

The project was funded through a one-year grant from the California Energy Commission. EDI integrated its drive train into the 14,500-pound medium-duty Greenkraft CNG truck. As a result, the vehicle has a 40-mile range operating as an all-electric vehicle.

In Canada, the Union Gas utility recently opened a CNG fueling station for Hamilton, ON's street railway buses. The station is located at Hamilton's Mountain Transit Centre, offering enough capacity to allow the city's fleet of NGV buses to grow from the current 35 to up to 120 vehicles during the next six years.

City officials are projecting up to $40 million in savings over the next 20 years from the increased use of CNG buses. They also project that GHG emissions will be lower about 25% over the period. The city plans to add 24 40-foot CNG Nova buses early next year.

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