Aftertreatment systems and methods for treatment of exhaust gas from diesel engine

An aftertreatment system to treat exhaust gas from a diesel engine, comprising:

• a selective catalytic reduction catalyst on a diesel particulate filter (SCR-F);
• a first reductant injector connected to an exhaust gas passage upstream of the SCR-F;
• a downstream diesel oxidation catalyst (DOC) disposed downstream of the SCR-F;
• a selective catalyst reduction catalyst (SCR) disposed downstream of the downstream DOC;
• a second reductant injector coupled to an exhaust gas passage and positioned between the downstream DOC and the SCR;
• and
• a controller to calculate a desired particulate matter (PM) oxidation rate in the SCR-F and a desired system NOx conversion efficiency based on engine speed and load conditions, to determine a first ammonia to NOx ratio to the SCR-F and a second ammonia to NOx ratio to the SCR based on (i) the desired PM oxidation rate, (ii) the desired system NOx conversion efficiency, and (iii) states of the SCR-F, the downstream DOC and the SCR, and to determine a first reductant flowrate from the first reductant injector and a second reductant flowrate from the second reductant injector corresponding to the first ammonia to NOx ratio and the second ammonia to NOx ratio, respectively;
• wherein a reductant is a diesel exhaust fluid (DEF) solution, and wherein the states of the SCR-F, the downstream DOC and the SCR include temperatures, PM concentrations and NOx concentrations of the exhaust gas as the exhaust gas flows through the SCR-F, the downstream DOC and the SCR, respectively.

A method to operate an aftertreatment system for a diesel engine, the aftertreatment system including a SCR-F, a SCR downstream of the SCR-F and a downstream DOC disposed between the SCR-F and the SCR, the method comprising:

• determining a desired PM oxidation rate in the SCR-F and a desired system NOx conversion efficiency based on engine speed and load conditions;
• determining a first reductant flowrate from a first reductant injector positioned upstream of the SCR-F and a second reductant flowrate from a second reductant injector positioned upstream of the SCR based on the desired PM oxidation rate, the desired system NOx conversion efficiency, and changes of PM mass retained, NOx concentrations and temperatures as exhaust gas flows through the SCR-F, the downstream DOC and the SCR;
• and
• determining the first reductant flowrate based on a first ammonia to NOx ratio and a first inlet NOx concentration to the SCR-F, a first inlet exhaust gas temperature in an exhaust gas passage upstream of the SCR-F, and an exhaust flow rate to the SCR-F;
• and determining the second reductant flowrate based on a second ammonia to NOx ratio and a second inlet NOx concentration to the SCR, a second inlet exhaust gas temperature in an exhaust gas passage upstream of the SCR and an exhaust flow rate to the SCR.