US Patent 7340888 Diesel particulate matter reduction system

A diesel exhaust treatment system is disclosed that includes first and second diesel particulate reduction devices. The first diesel particulate reduction device is located upstream in the exhaust flow and contains an oxidation catalyst coating. The second particulate reduction device is located downstream from the first particulate reduction device and is generally non-catalyzed or lightly catalyzed. Each particulate reduction device comprises a flow-through fabric-type filtration media with substantial internal turbulence. As exhaust gas passes through the catalyzed upstream particulate reduction device, nitric oxide (NO) is oxidized to form nitrogen dioxide (NO2), a portion of which interacts with the particulate trapped within the upstream diesel particulate reduction device to regenerate the upstream device. A remaining portion of exhaust gas containing NO2 enters the downstream diesel particulate reduction device, where an additional portion interacts with the trapped particulate to regenerate the device. The relative volume weighted efficiency of the upstream particulate reduction device and of the downstream particulate reduction device are selected to optimize the overall system particle capture efficiency and backpressure, as well as to balance the amount of NO2 made with the amount of NO2 consumed so as to minimize NO2 emissions.