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During recent years, the deterioration of greenhouse phenomenon, in conjunction with the continuous increase of worldwide fleet of vehicles and crude oil prices, raised heightened concerns over both the improvement of vehicle mileage and the reduction of pollutant emissions. Diesel engines have the highest fuel economy and thus, highest CO2 reduction potential among all other thermal propulsion engines due to their superior thermal efficiency. However, particulate matter (PM) and nitrogen oxides (NOx) emissions from diesel engines are comparatively higher than those emitted from modern gasoline engines. Therefore, reduction of diesel emitted pollutants and especially, PM and NOx without increase of specific fuel consumption or let alone improvement of diesel fuel economy is a difficult problem, which requires immediate and drastic actions to be taken.

A method to curtail emissions of smoke and other pollutants from diesel engines is to enhance the oxygen supply to their combustion chamber. This can be accomplished by enriching either the intake air stream or the fuel stream with oxygen. Experimental studies concerning the oxygen-enrichment of intake air, have revealed large decrease of ignition delay, drastic decrease of soot emissions as well as reduction of CO and HC emissions while, brake specific fuel consumption (BSFC) remained unaffected and increasing of power output is feasible. However, this technique was accompanied by considerable increase of NOx emissions. Experimental and theoretical studies with oxygenated fuels have demonstrated large decrease of soot emissions, which correlated well with the fuel oxygen content. Reduction of CO and HC emissions with oxygenated fuels was also obtained. However, penalties in both BSFC and NOx emissions have been observed with oxygenation of diesel fuels.

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.

This work determined the suitability of two silicon carbide (SiC) monoliths (one regular and one coated with a micromembrane), as well as a coated cordierite monolith for use as aerodynamically regenerated particulate filters for diesel engines. These ceramic honeycomb monoliths were tested for their filtration efficiency, their post filtration particulate size distribution and their ability to be aerodynamically regenerated at pre-selected operating temperatures (200, 300 and 400°C). Through combined laboratory and field testing, the uncoated silicon carbide filter produced the most satisfactory results in all of these tests. This filter resulted in excellent regeneration characteristics while maintaining the highest filtration efficiencies at all particle sized tested. All filters were found to clean effectively at all temperatures. However, upon normalization with the volumetric flow rate through the monolith, it was found that the filters were most thoroughly cleaned at 400°C.