Patent ID: 8783019

Claim:
An engine exhaust treatment system fluidly coupled to an internal combustion engine, comprising: an oxidation catalyst disposed in an engine exhaust stream; a reductant source for injecting a reductant into the exhaust stream downstream of the oxidation catalyst; an SCR catalyst disposed in the exhaust stream downstream of the reductant source; and a gas sensor, disposed in the exhaust stream downstream of the oxidation catalyst and upstream of the reductant source, comprising a plurality of sensing or pumping cells, wherein a first cell is capable of producing a first output that is indicative of a concentration of NO 2 alone or in combination with one or more other constituents, and a second cell is capable of producing a second output that is indicative of a concentration of NO alone or in combination with one or more other constituents, and further wherein if the first output is indicative of the concentration of NO 2 in combination with one or more other constituents, the sensor comprises cells with sensing capabilities sufficient to isolate the contribution of NO 2 concentration to said first output, and if the second output is indicative of the concentration of NO in combination with one or more other constituents, the sensor comprises cells with sensing capabilities sufficient to isolate the contribution of NO concentration to said second output.