Effect of Fuel/Air Ratio Variations on Catalyst Performance and Hydrocarbon Emissions During Cold-Start and Warm-Up

• Published in: SAE transactions Vol. 105; pp. 2036 - 2063
• Main Authors: Drake, Michael C., Sinkevitch, Robert M., Quader, Ather A., Olson, Keith L., Chapaton, Thomas J.
• Format: Journal Article
• Language: English
• Published: Society of Automotive Engineers, Inc 01-01-1996
• ISSN: 0096-736X; 2577-1531

Effects of fuel/air equivalence ratio variations (Φ - 1.0±0.02) on engine-out and catalyst-out hydrocarbon (HC) mass and speciated emissions were measured under simulated cold-start conditions in order to suggest ways to optimize the enginecontrols-catalyst system for minimum HC mass emissions and specific reactivity. A single-cylinder engine (installed in a temperature-controlled room and using commercial-grade gasoline) is run under controlled steady-state conditions (at 24 °C or -7 °C) which simulate cold starting. Speciated and total hydrocarbon emissions are measured from engine-out exhaust samples and from samples taken after an oven-temperature-controlled catalyst (either a fresh platinum/rhodium production catalyst, a 50,000 mile vehicleaged catalyst, or a ceramic brick with standard washcoat containing no noble metal). Changes in engine fuel/air equivalence ratio (Φ - 1.0±0.02) have a small effect on engine-out HC mass emissions (± 10 %) and specific reactivity (0 - 2%). However, changing Φ from 1.02 (slightly rich) to 0.98 (slightly lean) has a large effect on catalyst performance - decreasing post-catalyst ozone forming potential values by a factor of 36 for a fresh catalyst and a factor of 6 for an aged catalyst.