Patent ID: 6854264

Claim:
A system for an engine having at least a first group and a second group of cylinders, the system comprising: an emission control device coupled to said first and second groups of cylinders; and a computer storage medium having a computer program encoded therein for controlling fuel injected into the first and second group of cylinders, comprising: code for, during a first interval, operating in a first mode where said first group of cylinders is lean of stoichiometry and said second group of cylinders is at a first air-fuel ratio at stoichiometry or rich of stoichiometry; code for, during a second interval, operating in a second mode where said second group of cylinders is at a second air-fuel ratio rich of stoichiometry and richer than said first air-fuel ratio; code for repeatedly switching between said first and second mode to reduce sulfur contamination of said emission control device; and code for adjusting both said first and second air-fuel ratio values based on an exhaust temperature and engine flow.