An Investigation of Emission Species over a Diesel Oxidation Catalyst Using Flow Reversal Strategy

With the increasing demand of emission reductions from the automotive industry, advanced after-treatment strategies have been investigated to overcome the challenges associated with meeting increasingly stringent emission regulations. Ongoing investigations on low temperature combustion (LTC) strategies are being researched to meet future emission regulations, however, the lowered exhaust temperature presents an even greater issue for exhaust after-treatment due to the change in combustion modes. Catalyst temperature is critical for the catalytic ability to maintain effective conversion efficiency of regulated emissions. The use of periodic flow reversal has shown benefits of maintaining catalyst temperature by alternating the exhaust flow direction through the catalytic converter, reducing the catalyst sensitivity to inlet gas temperature fluctuations. Cyclically alternating the exhaust flow direction can produce a thermal wave, elevating the central catalyst temperature above the inlet gas temperature. In this work, analysis is conducted with a diesel oxidation catalyst (DOC) contained within a flow reversal system on a steady state heated flow-bench under simulated engine exhaust conditions. The investigation revealed that the improved heat retention of the flow reversal system translates to improved catalyst conversion efficiency, a decrease in carbonyl group and aromatic hydrocarbon species as well as greater hydrogen yield to that of passive unidirectional exhaust gas flow.