| abstract |
An exhaust purification system for the reduction of emissions from an exhaust stream comprises an oxygen detection system, such as an oxygen sensor, a catalyst, and an air injection system between the oxygen detection system and the catalyst. Air is injected into the exhaust stream at designated exhaust conditions to protect the catalyst from oxygen-deprived conditions. A controller includes instructions to inject air upon detection of exhaust stream oxygen level below a minimum oxygen level. The minimum oxygen level may be a level of oxygen above that required for complete combustion of all injected fuel, such as 1wt% oxygen or greater, such as about 10wt%. A method of reducing emissions from an exhaust stream comprises detecting an oxygen level upstream of a catalyst, and injecting air upstream of the catalyst at designated exhaust conditions. The designated conditions may be a rich air-fuel ratio. The catalyst may be a NOx storage catalyst or a cold start catalyst. |