Fuel efficiency optimisation based on boosting control of the particulate filter active regeneration at high driving altitude

The air pressure change as a function of the driving altitude affects negatively the engine performance and emissions as well as the efficiency of the exhaust aftertreatment systems (ATS). These detrimental effects have driven the emissions standards to account for the altitude as boundary condition in type-approval tests. The new requirements demand to balance the recovery of the engine performance as the altitude increases by means of control strategies avoiding negative effects on tailpipe emissions, i.e. combination of engine-out emissions and ATS performance. In this context, this study identifies experimentally the need of optimisation of the active regeneration strategies applied to wall-flow particulate filters for altitude driving. Firstly, a particulate filter was subjected to active regenerations at altitudes ranging from sea-level to 2500 m for a variety of initial soot loads. As boundaries, the engine worked according to the series calibration, which was found to be a function of the altitude for the boosting system actuation. The results evidenced a noticeable deterioration of the soot oxidation rate as the altitude increased. In fact, some operating conditions showed an early balance between filtration and oxidation that avoided the completeness of the regeneration process. The root causes of the soot depletion rate reduction, which involved thermal and transport phenomena, are reasoned from the combined analysis of experimental and modelling approaches. The conclusions provided a guide to successfully conduct the turbine actuation for an optimum exhaust thermal management during the regeneration event at altitude.