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The aim of this paper is to analyze the quantitative impact of fuel sulfur content on particulate oxidation catalyst (POC) functionality, focusing on soot emission reduction and the ability to regenerate. Studies were conducted on fuels containing three different levels of sulfur, covering the range of 6 to 340 parts per million, for a light-duty application. The data presented in this paper provide further insights into the specific issues associated with usage of a POC with fuels of higher sulfur content. A 48-hour loading phase was performed for each fuel, during which filter smoke number, temperature and back-pressure were all observed to vary depending on the fuel sulfur level. The Fuel Sulfur Content (FSC) affected also soot particle size distributions (particle number and size) so that with FSC 6 ppm the soot particle concentration was lower than with FSC 65 and 340, both upstream and downstream of the POC.

Under on-road driving conditions, the engine load and speed and the cooling effect of ambient air may affect the functioning of exhaust aftertreatment devices. In this paper, we studied the effects of these parameters on the functioning of the combination of a Diesel Oxidation Catalyst and a Particle Oxidation Catalyst (DOC+POC). In the engine tests, the engine load and speed were observed to affect the nonvolatile particle reduction efficiency curve of the DOC+POC; while the nonvolatile core particle (Dp ≺ 15 nm) reduction was high (97-99%) in all the engine test modes, the reduction of soot varied from 57% at low load to 70% at high load. Because the change in engine load and speed affected both the exhaust temperature and flow velocity, the effects of these parameters were measured separately in an aerosol laboratory.

Particle emissions have been generally associated to diesel engines. However, spark-ignition direct injection (SI-DI) engines have been observed to produce notable amounts of particulate matter as well. The upcoming Euro 6 legislation for passenger cars (effective in 2014, stricter limit in 2017) will further limit the particulate emissions from SI engines by introducing a particle number emission (PN) limit, and it is not probable that the SI-DI engines are able to meet this limit without resorting to additional aftertreatment systems. In this study, the solid particle emissions of a SI-DI passenger car with and without an installed Particle Oxidation Catalyst (POC®) were studied over the New European Driving Cycle (NEDC) on a chassis dynamometer and over real transient acceleration situations on road. It was observed that a considerable portion of particle number emissions occurred during the transient acceleration phases of the cycle.