Particulate Emissions in GDI Vehicle Transients: An Examination of FTP, HWFET, and US06 Measurements

With increasingly stringent light duty particulate emissions regulations, it is of great interest to better understand particulate matter formation. Helping to build the knowledge base for a thorough understanding of particulate matter formation will be an essential step in developing effective control strategies. It is especially important to do this in such a way as to emulate real driving behaviors, including cold starts and transients. To this end, this study examined particulate emissions during transient operation in a recent model year vehicle equipped with a GDI engine. Three of the major federal test cycles were selected as evaluation schemes: the FTP, the HWFET, and the US06. These cycles capture much of the driving behaviors likely to be observed in typical driving scenarios. Measurements included particle size distributions from a TSI EEPS fast-response particle spectrometer, as well as real-time soot emissions from an AVL MSS soot sensor. The study also examined mass comparisons to filter weights, and the specific behaviors during the cold start phase of the FTP cycle. The experiments showed that the exhaust particle size distribution was highly dependent on the testing cycle conditions. In particular, the number and type of modes present appeared to be related to the magnitude and frequency of aggressive acceleration events. The soot emissions data showed excellent test cycle event tracking, with cold start soot concentrations being orders of magnitude greater than in typical warm operation. Four repetitions of each cycle were conducted as a means of assessing repeatability, with consistent behaviors being observed.