| Abstract |
The Washington Metropolitan Area Transit Authority serves the public transportation needs of metropolitan Washington, D.C., including Northern Virginia and Southern Maryland. Because the EPA has classified this area as a severe ozone non-attainment area, WMATA is continually working to reduce local air pollution while providing reliable, low-cost service to its customers. A variety of low-emission bus technologies can help WMATA, and other transit agencies, achieve these goals. Among these options are compressed natural gas (CNG) buses and low-sulfur diesel buses equipped with advanced emission control technologies. A total of twelve 40-foot, low-floor WMATA buses were tested using West Virginia University's Transportable Heavy-Duty Vehicle Emission Testing Laboratory. These buses were of two types: CNG and low-sulfur diesel (approximately 17 ppm sulfur). All CNG buses had lean burn natural gas engines and oxidation catalysts. All diesel buses had catalyzed particulate filters, and one group of diesel buses had exhaust gas recirculation (EGR). The buses were tested for numerous regulated and unregulated emissions, including hydrocarbons, carbon monoxide, oxides of nitrogen (NOx), particulate matter (PM), and various toxic emissions. The increasingly strict EPA and California standards set for NOx and PM, particularly NOx, are considered to be the greatest challenge for heavy-duty engines. NOx is also of particular concern to the Metropolitan Washington, D.C., area because this area's ozone problem is considered to be largely NOx limited. As such, most of its air quality control measures are focused on an overall NOx reduction strategy. All buses were tested over the WMATA cycle, a custom drive cycle designed to represent real-world operation of the WMATA buses. The following are the four test bus configurations included in the study: CNG buses with model year (MY) 2004 John Deere 6081H engines, equipped with oxidation catalysts; CNG buses with MY 2001 Cummins Westport, Inc. (CWI) C Gas Plus engines, equipped with oxidation catalysts; Diesel buses with MY 2004 Detroit Diesel Corporation (DDC) Series 50 engines, equipped with catalyzed particulate filters and EGR; Diesel buses with MY 2000 DDC Series 50 engines, equipped with catalyzed particulate filters. |
