Abstract
In the recent times, with the introduction of new green-house gas and therefore fuel economy based regulations gaining more stringency, the proportion of gasoline direct injection (GDI) vehicles in the US light duty vehicle market has been steadily on a rise with a direct consequence of this scenario resulting in greater increase in number count of the ultrafine particulate matter (PM) emissions. It is becoming ubiquitous to develop advanced filtration systems and related strategies for modern light duty powertrain platforms. Hence, a detailed assessment of the phenomenological characteristics of ultrafine PM and particle number (PN) emissions from a GDI platform versus a diesel platform becomes quite imperative. In the light of this requirement, to better understand the characteristics of ultrafine PM the present study has been primarily focused on two parts – a) characterization of particulate number count and size distribution during transient operations in two recent year model vehicles, one of them being a diesel vehicle equipped with a filtration trap and the next being a GDI vehicle, without a particulate trap system; b) electron microscopic analysis of the soot particles recorded from both the candidate vehicles, and thereby examination of their respective morphology and structural characteristics. Characterizing the time averaged PN emissions resulting from transient operating conditions, it was observed that in GDI vehicle medium load transients (30 mph-40 mph) contributed most substantially to the elevated PN levels, with concentration of PN emissions greater than one order magnitude as compared to PFI vehicle. Overall, the GDI vehicle emissions consisted of averaged particles with mean diameter at 52nm for urban like driving conditions whereas smaller particles around 10nm were dominating the highway driving phase. Furthermore, to this discussion the paper will also include comparative analysis of size and morphology of solid particles from AFM/SEM images, between different types of transient drive cycles that will lead to better understanding of PM formation in GDI engines during highly transient vehicle activity.
Keywords: real-world emissions, particle number, PEMS, GDI, RDE