O Emissions of Low Emission Vehicles
The Environmental Protection Agency (EPA) and Department of Transportation's National Highway Traffic Safety Administration (NHTSA) have finalized regulation that will reduce greenhouse gases and increase fuel economy for model year (MY) 2012-2016 light-duty vehicles. This ruling not only includes a CO₂ standard that will require vehicles to achieve fleet average 35 mpg by MY 2016, but will apply a cap on nitrous oxide (N₂O) and methane emissions to 10 and 30 mg/mile, respectively, however CO₂ emission reductions can be exchanged for either N₂O or methane credit. The work outlined investigates the N₂O emissions of a variety of low emission vehicles per the Federal Test Procedure (FTP). Fourier Transform Infrared Spectroscopy (FTIR) was used to measure both bag and modal N₂O emissions. N₂O emissions were less than 1 mg/mile for three SULEV vehicles with 6,400 km-aged catalysts. For 240,000 km equivalent dynamometer-aged catalyst systems, N₂O emissions varied from 1.3 to 8 mg/mile on various low emission vehicles. Both close-coupled and underfloor catalysts can generate N₂O emissions especially during the cold and warm engine starts. Most catalysts stop generating N₂O when catalyst temperatures exceed 450°C. However steady-state production of N₂O was observed at 550÷C. Fast light-off strategies appear to minimize N₂O emissions. Turbocharged vehicles with lower catalyst bed temperatures generate greater amounts of N₂O emissions. This work will also show that catalyst technology can effect tailpipe N₂O emissions.