Study on Filter Substrate Structure for Lower Backpressure and Higher Regeneration Performance

The trade-off between NOx and particulate matter (PM) has been a technological challenge with respect to diesel engine emissions. However, the practical use of diesel particulate filters (DPF) has made diesel emission control possible, in which NOx emissions are reduced through engine control and nearly all emitted PM is completely removed by DPF from diesel exhaust emissions. This has helped to contribute to laying the foundation for pursuing of the high theoretical thermal efficiency of diesel engines. However, it is also a fact that such emission controls have resulted in considerable impairments on the original and greatest advantages of diesel engines. This includes fuel penalties with accompanying increases in fuel consumption caused by pressure losses due to the attachment of the DPF itself and the accumulation of PM in the DPF, as well as fuel losses that occur when fuel is used to regenerate collected PM. When fuel consumption penalties resulting from the installation of DPFs are examined for current DPF systems, the fuel loss caused by the forced regeneration gives a higher contribution than that caused by the pressure losses in current DPF systems. Especially, C-DPF systems have a higher proportion of the fuel loss by the forced regeneration than FBC system. Through the fundamental study on batch PM oxidation test, it was found that the PM regeneration activity was more due to differences in PM/catalyst contact rather than the activation energy of the catalyst based on the chemical reaction kinetics of the reaction of PM oxidation. The porous material which collects PM within the filter wall, not surface of the wall, made it possible to increase the oxidation rate of collected PM more than five times current levels by improving PM/catalyst contact. At the same time, it was found a possibility to achieve lower pressure loss by the deep-bed filtration.