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 (NO.sub.2), 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 NO.sub.2 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 NO.sub.2 made with the
amount of NO.sub.2 consumed so as to minimize NO.sub.2 emissions.