Air Pollution as a Climate Forcing: A Workshop
Day 3 Presentations
Particle Emissions from Motor Vehicles: Current and Future Technologies
Scientific Research Laboratory, Ford Motor Company, Dearborn, MI, U.S.A.
You may download a MS PowerPoint version (990 kB) of this presentation.
The diesel powered vehicle is presently at a crossroads. On one hand it is the most readily available powertrain technology to increase motor vehicle fuel economy in order to conserve energy resources, reduce dependence on foreign oil, and reduce greenhouse gas emissions. On the other hand its NOx and particulate matter (PM) emissions must be brought under control to meet upcoming tightened standards. Air quality and health concerns have been the principal drivers towards lower ambient and emissions standards. Recently, attention has also turned towards the climate change impacts of pollutants. Hydrocarbon and sulfate aerosols, and black carbon derived from motor vehicle emissions (and combustion sources in general) are currently being studied to understand their contributions to radiative forcing.
PM emissions vary widely with powertrain technology, fuel, engine operation, and exhaust dilution. For light duty vehicles, mass emissions over the federal test cycle (FTP) range from 50 - 80 mg/mi for diesel vehicles to 0.5 - 2 mg/mi for current model gasoline vehicles. The figure illustrates particle number emissions vary between diesel, gasoline direct injection, and conventional gasoline vehicles (steady state tests). The particle size ranges from <10 to ~500 nm in diameter for all of the engine types, typical of combustion PM. In general, the size distributions are bimodal: The mode typically centered at 50 - 90 nm and lognormal in shape is the soot mode, and the mode centered at 10 - 30 nm arises from nucleation. The soot mode arises in the engine from the combustion process, can be reproducibly measured, and consists of black carbon coated to a variable degree with condensed hydrocarbons and sulfate. The nuclei mode is highly variable, depending on fuel type, exhaust dilution conditions, and numerous other factors. The PM composition also varies with engine type. Diesel PM generally consists of ~65% black carbon and ~35% organic carbon. This split is roughly the opposite for gasoline vehicles.
PM emissions standards have recently been drastically lowered. U.S. light duty vehicles must meet a 10 mg/mi standard, down from 80 mg/mi. And heavy duty vehicles must meet a 20 mg/mi standard, whereas past emissions might have reached g/mi levels. Particle trap technologies have been developed to achieve these low emissions. For light duty vehicles, they appear to be able to reduce diesel engine PM levels to those typical of gasoline vehicles.