Interactions between aftertreatment systems architecture and combustion of oxygenated fuels for improved low temperature catalysts activity

Diesel engine vehicles, despite their good fuel economy and reduced CO2, are receiving significant attention and negative publicity in recent years due to their difficulties in achieving the emissions regulations. This has widely been linked to undesirable environmental impact and health effects. The lower exhaust gas temperatures associated with modern and more efficient hybrid powertrain and diesel engines makes current technology catalytic aftertreatment systems less efficient under range of vehicle operating conditions. This study, demonstrates how changes in the commonly used aftertreatment system architecture and changes in fuel composition in this case through the addition of oxygenated fuels (i.e. butanol) in diesel fuel can provide meaningful low temperature catalyst activity improvements. The catalyst oxidation kinetics of CO and HC species were improved (reduced the light-off temperature by around 20 degrees C) when a diesel particulate filter (DPF) was placed upstream of the DOC, while the combination of DPF and combustion of oxygenated fuel in diesel led to up to 80 degrees C improvement in catalyst activity. The prevention of soot reaching the DOC active sites increases the rate of reactions and the species accessibility to the active sites of the catalyst, and thereby the oxidation of emissions (CO, HC, and NO) can occur at lower catalyst temperatures. The combustion of diesel-butanol blend further improved the DOC low temperature activity. The major contributors to the improved catalyst light-off, are the reduced level of soot and hydrocarbon emissions as well as the higher reactivity of the hydrocarbons species emitted under butanol blend combustion.