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The control over particulate emissions is becoming increasingly important in modern diesel engines for Heavy Duty applications, that will comply to more and more stringent emissions norms. Use of particulate traps is an effective means of achieving this with the need to regenerate the particulate trap being imperative. Passive regeneration using NO2 by conversion of NO, as well as regeneration at lower temperatures with catalyzed DPF and the influence of NOx to soot ratio on this, is the subject of the paper. Both coated and uncoated filters in fresh and aged state are evaluated at temperatures typical of passive NO2 and Oxygen-based soot regenerations and the results discussed.

1 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.

New catalysts with HC (hydrocarbon) storage ability to improve NOx conversion and to minimize fuel penalty over the US Heavy Duty Transient cycle were developed. Without secondary fuel addition, simultaneous reduction of 13% NOx and about 30% particulate was achieved by storing HC from the engine during low temperature portions of the transient cycle and releasing and using the stored HC for NOx conversion at higher temperatures. With only 1% secondary fuel addition, NOx reduction can be increased to 25%, and the particulate conversion remained relatively constant at about 20%. More than 30% NOx reduction can be obtained with 3% fuel penalty. All the pollutants (NOx, PM, HC and CO) were reduced with 0-1 % secondary fuel addition.