Patent ID: 8875494

Claim:
A method for an engine, comprising: adjusting an amount of fuel supplied to at least one engine cylinder in response to determining that soot is being oxidized in a particulate filter, the determination based on comparing an oxygen concentration of exhaust gases entering the particulate filter with an oxygen concentration of exhaust gases exiting the particulate filter and entering a catalyst arranged downstream of the particulate filter; maintaining the catalyst at stoichiometric conditions during the fuel amount adjustment; and spark igniting at least some of the amount of fuel in said at least one cylinder; wherein said adjusting an amount of fuel supplied to at least one cylinder includes varying a distribution of fuel about a stoichiometric air-fuel mixture, wherein said distribution is varied in response to a measured oxygen storage capacity of the catalyst located downstream of said particulate filter; wherein an amount of time or number of combustion events that said engine is operated lean of stoichiometry while oxidizing said soot is related to said measured oxygen storage capacity of said catalyst; and wherein the distribution of fuel is varied responsive to said measured oxygen storage capacity such that said measured oxygen storage capacity is not depleted or filled while the particulate filter oxidizes soot.