A large study comparing trucks fuelled by natural gas with others fuelled by diesel found the natural gas vehicles produced only a quarter of the carbon monoxide emissions and half the oxides of nitrogen emissions of their diesel counterparts.
The study was conducted using package trucks operated by United ParcelService (UPS), which operates America’s largest private compressed natural gas (CNG) fleet.
The study compared the operations, maintenance, performance, and emissions characteristics of CNG and diesel vehicles from 1997 to 2000, as part of the broader US Department of Energy/National Renewable Energy Laboratory (DOE/NREL) Truck Evaluation Project.
The CNG trucks ran every working day with no major complaints and were used as much or more than the diesel trucks.
Compared with diesel truck emissions, CNG truck carbon monoxide emissions were 75 percent lower, oxides of nitrogen 49 percent lower, hydrocarbons and non-methane hydrocarbons 4 percent lower, and carbon dioxide 7 percent lower.
Total operating costs of CNG trucks were 2 percent lower than total operating costs of diesel trucks at one of the study sites and 19 percent higher at the other site.
Because the CNG trucks were built with early production technology, they had a 27 to 29 percent lower energy equivalent fuel economy than diesel trucks. Newer technology can reduce this deficit to as low as 10 to 15 percent.
All study results are detailed in UPS CNG Truck Fleet: Final Results. The report is available online at: <A HREF=’http://www.ctts.nrel.gov/heavy_vehicle/pdfs/31227.pdf’>UPS Report</A>