Since the mid-1990s, light-duty vehicles equipped with gasoline
direct injection (GDI) engines have been added to the vehicle fleet
in increasing numbers. Compared to conventional port fuel injection
(PFI) engines, GDI engines provide higher power output for the same
size engine, higher fuel efficiency, and lower carbon dioxide (CO₂)
emissions. Due to the paucity of particulate matter (PM) emission
data for light-duty gasoline vehicles in general and the increasing
interest in these emissions relative to climate and air quality
concerns, it is important to investigate PM emissions from
current-generation GDI technologies. In this study, nine 2007-2010
light-duty GDI vehicles equipped with either wall-guided or
spray-guided fuel injection systems were tested using California
commercial gasoline fuel containing six percent ethanol by volume.
Criteria pollutants including gaseous and PM emissions were
measured over the Federal Test Procedure (FTP) transient test
cycle. Two real-time particle measurement systems were utilized to
measure solid and total particle number emissions.
Test results show that PM emissions for first-generation GDI
vehicles tested are significantly higher than PFI vehicles
certified to California Low Emission Vehicle (LEV) II standards. In
phase 1 of the FTP cycle during engine cold-start, PM mass
emissions for the nine GDI vehicles ranged from 4 to 35 mg/mi, with
an average of 14 mg/mi. The average FTP-weighted PM emissions for
these GDI vehicles are 10 times higher than LEV II PFI vehicles
tested previously. Over the FTP cycle, particle size distribution
is bi-modal for the spray-guided GDI vehicle, and accumulation mode
particles dominate particle emissions for the wall-guided GDI
vehicle.
