Characterization of On-Road Emissions of Compressed Natural Gas and Diesel Refuse Trucks

Portable emission measurement systems were used to perform on-road emissions testing of compressed natural gas (CNG) and diesel refuse trucks to determine whether replacing diesel-fueled refuse trucks with CNG-fueled trucks would reduce emissions and fuel consumption. Two types of on-road testing were conducted: one while performing actual garbage collection in a service area (in-service testing) and the other following predeveloped duty cycles (duty cycle testing). Carbon dioxide (CO₂), gaseous pollutants [oxides of nitrogen (NO_x), carbon monoxide (CO), and hydrocarbons (HC)], and particulate matter (PM) emissions as well as carbon-based fuel consumption from refuse trucks during both types of testing were measured and analyzed. The analyzed results showed that CNG refuse trucks generally produced about 20% lower CO₂ emissions and significantly lower NO_x emissions compared with diesel trucks. However, CNG trucks emitted more CO and HC than diesel trucks. Almost all measured HC and PM emissions from diesel trucks were negligible. Measured PM emissions from CNG trucks were also negligible. Detailed tests and analyzed results are presented in this paper.