Valveless dual leg exhaust aftertreatment system

A method of treating engine exhaust, comprising:

• channeling the exhaust through a leading exhaust conduit;
• splitting the exhaust from the leading exhaust conduit into two or more branches at least one branch containing a NOx adsorber-catalyst;
• and
• from time-to-time, regenerating the NOx adsorber-catalyst by injecting reductant into the NOx adsorber-catalyst's corresponding branch upstream of the NOx adsorber-catalyst;
• wherein the exhaust flow is allowed to divide between the branches only according to factors consisting essentially of factors selected from the group consisting of the temperature-dependent friction factors attributable to the fixed geometries of the branches including the devices they contain, the effects of reductant and exhaust flows in the branches, and temperature actuated dampers.

A method of operating a NOx adsorber-catalyst in one of the branches of an exhaust aftertreatment system having two or more branches each branch containing an in-line reformer upstream of a NOx adsorber-catalyst, the two or more branches separating upstream of the reformers and rejoining downstream of the NOx adsorber-catalysts, comprising:

• allowing a first portion of the exhaust to flow into the one branch and a second portion of the exhaust to simultaneously flow into a second branch;
• adsorbing NOx from the exhaust in the one branch using the NOx-adsorber-catalyst in the one branch during a lean phase;
• injecting a fuel into the one branch to begin a reformer warming phase;
• combusting the fuel in the reformer in the one branch to warm the reformer;
• increasing the fuel flow rate to initiate a rich phase;
• regenerating the NOx adsorber-catalyst in the one branch;
• and
• terminating the fuel flow to begin a new lean phase;
• wherein the average proportion of the exhaust flowing into the one branch during the rich phase is at least about 50% of the average proportion of the exhaust flowing into that branch during the lean phase.