A highly robust Diesel Oxidation Catalyst (DOC) for use with a dual mode combustion system, which makes it possible to switch the combustion between conventional mode and PCI (Premixed Compression Ignition) Combustion mode, was studied.
Firstly, commercially available DOCs were tested to confirm current level of emission reduction efficiency for a simulated dual mode combustion system, where CO (Carbon monoxide) was varied from 500 to 5,000 ppm, HC (Hydrocarbon) was varied from 500 to 5,000 ppmC and O2 (Oxygen) was varied from 2 to 15%, respectively. A commercially available Pt based DOC showed good CO and HC light-off performance at 500 ppm of CO and HC at up to 10% O2. However, it did not keep the superior light-off activity when CO and HC were increased to 5,000 ppm and O2 was decreased to 2%. A commercially available Pt-Pd based DOC demonstrated better light-off activity compared to the Pt based DOC at lower CO and HC concentrations. However, it also gave much poorer performance at elevated CO/HC conditions, similar to the Pt based DOC.
In order to improve the robustness in light-off activity, a new DOC was developed with novel design features, considering various performance aspects. The effectiveness of the novel design concept was verified in a model gas activity test. The newly developed DOC demonstrated effective CO and HC oxidation efficiency in both simulated conventional combustion and PCI combustion emissions, and it was greatly superior in comparison to commercially available Pt or Pt-Pd based DOCs. In addition to the advantage in CO and HC light-off activities, NO oxidation into NO2 at low temperature conditions was also improved over the newly developed DOC.
In this paper, as described above, applicability of commercially available DOCs for a dual mode combustion system is discussed, and technical constraints for the application of DOCs to the new combustion engine emissions is clarified. Finally, the effectiveness of a novel catalyst design concept is also discussed.