Regulated and Non-Regulated Emissions and Fuel Economy from Conventional Diesel, Hybrid-Electric Diesel, and Natural Gas Transit Buses

Distance-specific fuel economy (FE) and emissions of carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx), and particulate matter (PM) from transit buses representing diesel, retrofitted diesel, hybrid-electric diesel, and lean-burn natural gas technologies are presented in this paper. Emissions were collected from these buses at the Washington Metropolitan Area Transport Authority (WMATA) test site in Landover, Maryland. In this program, one bus each from diesel, retrofitted diesel, hybrid-electric diesel, and natural gas technologies was tested on 17 chassis cycles and the other buses were tested on a subset of these cycles. Data show that the test cycle has a profound effect on distance-specific emissions and FE, and relative emissions performance of technology is also cycle dependant. Lean-burn natural gas buses demonstrated their low PM output, diesel engines showed low HC output, benefit of exhaust filtration was evident, and the positive effect of hybrid-electric drive technology was most pronounced for low-speed transient cycles.