Use of Ozone-Enriched Air for Diesel Particulate Trap Regeneration 1999-01-0114

This manuscript describes laboratory tests and calculations that explore the effectiveness of a stream of ionized air to oxidize soot and, thus, regenerate diesel particulate filters. Soot was oxidized inside a muffle furnace in two different configurations, either as a layer of soot spread in a porcelain boat, or as a quantity of soot evenly loaded in a ceramic wall-flow monolith. Oxidation took place in air, ozone-enriched air or air ionized by an electric arc (thermal plasma), at furnace temperatures in the range of 200-450° C. It was found that when ozone was generated in the inlet air (1060 ppm) the consumption rate of soot increased by up to ten percent. However at the presence of the thermal plasma (generating O, NO₂, NO, and O₃) the carbon consumption was accelerated by factors varying from a few percent to often exceeding one hundred percent. The effectiveness of this technique depended on the characteristics of the arc. Moreover, the oxidation rate increased with increasing furnace temperature. Results also showed that the oxidation of diesel soot was much faster than that of pure carbon black and that the effect of the generated oxidizing species (O, O₃ NO₂, etc.) was more pronounced in the case of diesel soot. The present ozone generator consumed 10 W of electric power and the electric arc transformer was rated at 220 W. So far the results of this work suggest that the effect of ozone in oxidizing soot is minor, in this temperature range, while the effect of other oxidizing species (O, NO₂) could be significant. In vehicle applications the effluent of a particulate trap regenerated with this technique must be scrutinized, as it may contain toxic pollutants such as NO2. If the regeneration is performed off-line, the effluent of the trap may be channeled back to the engine, where further reactions may minimize the pollutants.