Effects of Fuel Sulfur on FTP NOx Emissions from a PZEV 4 Cylinder Application

FTP emissions were measured on a 2009MY, 4 cylinder 2.4L Malibu PZEV vehicle with 3 and 33 ppm sulfur fuel. The exhaust system employed one close-coupled and one under floor converter. FTP evaluations with Phase-II certification fuel with 33 ppm sulfur exhibited increasing NOx emissions with subsequent FTP evaluations (NOx creep). In an effort to minimize NOx creep, FTP preparation cycles and low sulfur fuels were investigated. Results indicate that utilizing the US06 cycle in between subsequent FTP's can mitigate NOx creep. FTP evaluations with 3 ppm sulfur fuel exhibited no NOx creep regardless of FTP preparation cycle and yielded overall lower NOx emissions.