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The influence of a platinum:palladium (Pt:Pd)-based diesel oxidation catalyst (DOC) on the engine-out particulate matter (PM) emissions morphology and structure from the combustion of alternative fuels (including alcohol-diesel blends and rapeseed oil methyl ester (RME) biodiesel) was studied. PM size distribution was measured using a scanning mobility particulate spectrometer (SMPS), and the PM morphology and microstructure (including size distribution, fractal geometry, and number of primary particles) was obtained using high-resolution transmission electron microscopy (TEM). It is concluded that the DOC does not modify the size or the microstructural parameters of the primary particulates that make up the soot agglomerates. The PM reduction seen in the DOC is due to the trapping effect, and oxidation of the PM's volatile components. The DOC performance in reducing gaseous (e.g., carbon monoxide (CO) and unburnt hydrocarbons (HCs)) and PM emissions at low exhaust temperatures was improved from the combustion of alternative fuels due to the reduced level of engine-out pollutants.

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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 °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 °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.

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