The influence of hydrogen over platinum and combined platinum-palladium diesel oxidation catalysts were investigated on the oxidation kinetics of CO, HC and NO. Although H 2 has been reported to have a positive effect on CO and HC oxidation as well as NO 2 formation over platinum catalysts, there is still uncertainty whether this is due to the temperature rise caused by H 2 oxidation or the result of a change in the reaction kinetics of CO, HC and NO oxidation by the production of intermediate species. The results have showed smaller H 2 concentrations are more effective in improving the catalyst light-off temperature as well as promoting NO oxidation over both platinum and platinum-palladium catalysts. It is suggested that these benefits are a result of not only the exothermic reactions which in turn increase the local catalyst temperature but also H 2 increasing the rate of reactions and the species accessibility to the catalyst active sites thus further CO, HC and NO oxidation can occur at lower catalyst temperatures.
Although exhaust gas recirculation (EGR) is an effective strategy for controlling the levels of nitrogen oxides (NO(X)) emitted from a diesel engine, the full potential of EGR in NO(X)/PM trade-off and engine performance (i.e., fuel economy) has not fully been exploited. Significant work into the cause and control of particulate matter (PM) has been made over the past decade with new cleaner fuels and after-treatment devices emerging to comply with the current and forthcoming emission regulations. In earlier work, we demonstrated that engine operation with oxygenated fuels (e.g., biodiesel) reduces the PM emissions and extends the engine tolerance to EGR before it reaches smoke-limited conditions. The same result has also been reported when high cetane number fuels such as gas-to-liquid (GTL) are used. To further our understanding of the relationship between EGR and PM formation, a diesel particulate filter (DPF) was integrated into the EGR loop to filter the recirculated soot particulates. The control of the soot recirculation penalty through filtered EGR (FEGR) resulted in a 50% engine-out soot reduction, thus showing the possibility of extending the maximum EGR limit or being able to run at the same level of EGR with an improved NO(X)/soot trade-off.
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