Effect of soot accumulation in a diesel particle filter on the combustion process and gaseous emissions

Particulate filters are massively used in new diesel vehicles to reduce particulate emissions below the regulation limits. The setting of filters in the exhaust lines imposes various changes in the engine working conditions, including increased back-pressure, resulting in some fuel penalty. In this work, the filter loading process was investigated in a modern common-rail diesel engine equipped with diesel oxidation catalyst and diesel particulate filter. The engine was fuelled with EN-590 diesel fuel and run in a highly emissive operating mode selected among those reproducing the New European Driving Cycle. During the test the intake/exhaust conditions, intake charge, injection and combustion timing, fuel consumption and regulated emissions were measured. It was observed that the EGR (exhaust gas recirculation) ratio decreased from 30% down to 21%, shifting the combustion process away from its design parameters. In consequence, nitrogen oxides emissions increased around 60% along the test, compromising the objectives of the emission regulations. A 4% increase in fuel consumption throughout the test was measured, this value being higher than that expected from previous literature. An energy balance revealed that such penalty was caused by increased pumping losses and, especially, by higher energy losses via exhaust gas temperature and engine coolant.