Improved Microwave-Susceptible Catalytic Diesel Particulate Filter

Abstract

Emission standards forced the manufacturers to adopt several aftertreatment devices as effective way to comply with the stringent limits for gaseous and particle emissions. The diesel particulate filter (DPF) is currently the usual aftertreatment system in Diesel engines for soot particle abatement. Among different filter solutions, flow-through filters, such as ceramic foams or open honeycomb structures, are characterized by low pressure drop but by a filtration efficiency of only 40 - 70%, while wall-flow monoliths, consisting in alternately plugged parallel square channels, so that the exhaust gases flow through the porous inner walls, showed the best balance between filtration efficiency and pressure drop performance. Since pressure loss increases with soot filtration, the DPF needs to be periodically regenerated by burning off the accumulated soot. In our previous work we showed that the simultaneous use of a microwave applicator and a specifically catalysed DPF with a catalyst load up to 30%wt of CuFe2O4, allows to reduce the temperature, the energy and the time required for the filter regeneration with respect to the uncatalysed filter. These results were more evident in particular by adding K to our catalyst formulation and by lowering gas flow rate during the regeneration step. Starting by these very promising results, a procedure to increase the initial medium pore diameter of the bare monoliths was optimized, so aiming at increasing the active species load: in this way the further reduction of soot oxidation temperature is possible, keeping acceptable the pressure drop, and, more important, allowing a decreased regeneration frequency of the filter. The feasibility of the microwave heating technology was also verified by comparing the energy balance of the entire process to the actually employed regeneration technologies.