An exhaust after-treatment system, comprising: a first set of exhaust after-treatment components; a second set of exhaust after-treatment components, the first set of exhaust after-treatment components comprising different types of exhaust after-treatment components than the second set of exhaust after-treatment components; an inlet to the exhaust after-treatment system; an outlet from the exhaust after-treatment system; and a valve and conduit arrangement configurable in a plurality of modes such that in a first mode, exhaust gas entering the inlet flows through the second set of exhaust after-treatment components, then through the first set of exhaust after-treatment components, and then through the outlet, in a second mode, exhaust gas entering the inlet flows through the second set of exhaust after-treatment components without flowing through the first set of exhaust after- treatment components, and then through the outlet, and characterized in that in a third mode, exhaust gas entering the inlet flows through the first set of exhaust after-treatment components, then through the second set of exhaust after- treatment components, and then through the outlet; at least one sensor for detecting at least one operating condition, and a controller configured to receive a signal from the at least one sensor corresponding to the at least one operating condition, the controller being configured to automatically configure the valve and conduit arrangement in the first mode when the at least one operating condition is in a first condition, and to configure the valve and conduit arrangement in the second mode when the at least one operating condition is in a second condition. a first set of exhaust after-treatment components; a second set of exhaust after-treatment components, the first set of exhaust after-treatment components comprising different types of exhaust after-treatment components than the second set of exhaust after-treatment components; an inlet to the exhaust after-treatment system; an outlet from the exhaust after-treatment system; and a valve and conduit arrangement configurable in a plurality of modes such that in a first mode, exhaust gas entering the inlet flows through the second set of exhaust after-treatment components, then through the first set of exhaust after-treatment components, and then through the outlet, in a second mode, exhaust gas entering the inlet flows through the second set of exhaust after-treatment components without flowing through the first set of exhaust after- treatment components, and then through the outlet, and characterized in that in a third mode, exhaust gas entering the inlet flows through the first set of exhaust after-treatment components, then through the second set of exhaust after- treatment components, and then through the outlet; in a first mode, exhaust gas entering the inlet flows through the second set of exhaust after-treatment components, then through the first set of exhaust after-treatment components, and then through the outlet, in a second mode, exhaust gas entering the inlet flows through the second set of exhaust after-treatment components without flowing through the first set of exhaust after- treatment components, and then through the outlet, and characterized in that in a third mode, exhaust gas entering the inlet flows through the first set of exhaust after-treatment components, then through the second set of exhaust after- treatment components, and then through the outlet; at least one sensor for detecting at least one operating condition, and a controller configured to receive a signal from the at least one sensor corresponding to the at least one operating condition, the controller being configured to automatically configure the valve and conduit arrangement in the first mode when the at least one operating condition is in a first condition, and to configure the valve and conduit arrangement in the second mode when the at least one operating condition is in a second condition.