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Particle Emissions from a 2009 Gasoline Direct Injection Engine Using Different Commercially Available Fuels
Abstract:
Total and solid particle mass, size, and number were measured in the dilute exhaust of a 2009 vehicle equipped with a gasoline direct injection engine along with an exhaust three-way-catalyst. The measurements were performed over the FTP-75 and the US06 drive cycles using three different U.S. commercially available fuels, Fuels A, B, and C, where Fuel B was the most volatile and Fuel C was the least volatile with higher fractions of low vapor pressure hydrocarbons (C10 to C12), compared to the other two fuels.
Substantial differences in particle mass and number emission levels were observed among the different fuels tested. The more volatile gasoline fuel, Fuel B, resulted in the lowest total (solid plus volatile) and solid particle mass and number emissions. This fuel resulted in a 62 percent reduction in solid particle number and an 88 percent reduction in soot mass during the highest emitting cold-start phase, Phasel, of the FTP-75, compared to Fuel C. Fuel B also resulted in the lowest particle formation during acceleration events. A complimentary modeling work [
10
] using the same fuel tested on this program showed a good correlation between the decrease in fuel high boiling point aromatics and double-bond equivalent value and the decrease in soot emissions.
Total PM mass emissions with all fuels, except the less volatile fuel, Fuel C, met the CARB proposed LEV III limit for 2014 and 2017, using the FTP-75. Engine operation with Fuels A and B met the CARB LEV III optional solid particle number limit for 2014, but the engine failed such limit using Fuel C and also failed the 2017 optional solid number limit using all fuels. This suggests a discrepancy between total PM mass limit and the solid particle number limit, with the latter limit being more stringent. A larger discrepancy also existed between the Euro 6 total PM mass limit and the solid particle number limit. Although the Euro 6 limit is based on the New European Driving Cycle (NEDC) and not the FTP-75, this GDI engine met the Euro 6 PM mass emissions over the FTP-75 and failed the solid particle number limit by a factor of 3 to 10 with the different fuels. This gross failure based on Euro 6 solid particle number limit, while passing the total PM limit, suggests that the Euro 6 PM regulations are mainly driven by the solid particle number emissions limit, with the total PM mass limit becoming less relevant.
This work showed that gasoline fuel physical and chemical properties play an important role in reducing PM emissions from a GDI engine. It also showed that cold-start and acceleration events dominated PM formation. Furthermore, this work highlighted discrepancies between solid particle number emissions limits and total PM mass emissions limits using the proposed optional CARB LEV III standard and the Euro 6 standard.