Advanced Emission Control Technologies for PM Reduction in Heavy-Duty Applications

In this paper results obtained with different particulate matter (PM) reduction technologies are presented. Diesel oxidation catalysts (DOC) are well known as a reliable PM reduction technology which can efficiently remove the soluble organic fraction (SOF) but which has no effect on the solid particles in PM. A drawback is that in combination with high sulfur fuel, oxidation of SO₂ to SO₃ by the DOC can occur, resulting in an increase of PM emissions.

An alternative technology that is proven to significantly reduce soot emissions comprises diesel particulate wall-flow filters. High filtration efficiencies of up to 90% and beyond are feasible. The main obstacle is the combustion of the trapped soot. As shown in this paper, the application of a catalyst coating to the filter aids the filter regeneration by lowering the balance-point temperature.

The main disadvantages of wall-flow filters are an increase in back-pressure and possible plugging caused by oil-ash accumulations. A potential solution that is presented in this paper is the newly developed continuous soot combustion catalyst (CSCC). This technology achieves higher PM conversions compared to conventional diesel oxidation catalysts. A key feature of this technology is the use of a special flow-through substrate possessing more porous walls and a higher geometric surface area than standard DOC substrates. With such substrates the residence time is increased, so that the trapped soot can be oxidized continuously by appropriately designed soot combustion catalysts.