Technical Paper
Reducing Catalyst Zone Flow for Robust Emissions Performance in the Presence of Engine Air Fuel Ratio Imbalance
2017-03-28
2017-01-0961
In recent years, the EPA has implemented a requirement for monitoring the air fuel ratio balance in multi-cylinder engines such that those imbalances may not be so great as to cause the tailpipe emissions level to exceed 1.5 times the nominal emissions standard. Such imbalances may be the result of production fuel injector variation, contamination, leaks, or other malfunctions which cause the air or fuel rate to vary across the cylinders controlled by a single oxygen sensor. For many diagnostic systems that rely on the signal from the oxygen sensor, to achieve compliance to the new diagnostic standard, the sensor must see the signal from each cylinder equally. The aftertreatment system must also be robust to individual cylinder air fuel ratio variation. This paper introduces the concept of catalyst zone flow, a condition in which different cylinders of a multi-cylinder engine use different portions of the catalyst brick.
