Exhaust Switch Without Moving Parts for Temperature Control of NOx-adsorbers

Temperature control is essential for lean NO_x-catalysts due to their limited maximum working temperature and their fast aging at high temperatures. Therefore, under high load efficient cooling is necessary. On the other hand light-up has to be fast, and cooling under low load has to be small.

This can be achieved by switching the exhaust flow between an insulated tube at low temperatures and a cooling element at high loads. Conventional systems consisting of a valve with actuator are expensive and might fail during life-time operation. Therefore, a purely passive flow switch without moving parts was designed. At low exhaust velocities the exhaust gas moves through an insulated central tube, whereas at high exhaust velocities the exhaust gas flows through an outer tube which acts as a cooling element.

The switching is characterized by the relative mass flow through the two ways as a function of total mass flow and temperature. The effects of certain geometric parameters on the switching are discussed.