Particle Emissions from Light Duty Vehicles during Cold-Cold Start and Identified from Ambient Measurements

Abstract

Particle emissions from motor vehicles are an increasing source of atmospheric pollution. Operating conditions that produce significant particle number emissions in light duty vehicles were the focus of this study. Extremely cold conditions cause engines to use significant fuel enrichment during starting and warm-up and thus are prone to high particle emissions. In gasoline direct injection engines, this can lead to even higher soot formation due to liquid fuel impingement on the cold surfaces of the combustion chamber and piston. Humans can be exposed to high particle concentration from cold starting vehicles in parking ramps or any busy traffic areas due to higher vehicle density and poor ventilation. Separating ambient particle emissions according to engine type allows for the identification of vehicles that have the highest tailpipe emissions or contribute to high ambient particle number (PN) concentration. This thesis presents the results of two studies. The first study shows that the average PN emitted during 180 seconds by GDI and PFI vehicles after a cold-cold start were 3.09E+13 and 2.12E+13 particles respectively, based on tailpipe out emissions. The high particle emissions highlight the need for better particle control strategies to reduce particle emissions during engine startup in cold ambient temperatures. Meanwhile, the ambient study conducted at the exit of a parking ramp found that GDI vehicles (only 12% of the vehicle population in this study) contributed to about 50% of the increase of particle concentrations associated with vehicles. Thus, the increasing number of GDI vehicles in the future is expected to lead to an increase in particle concentrations in parking ramps and similar facilities.