Analysis of particle mass and size emissions from a catalyzed Diesel particulate filter during regeneration by means of actual injection strategies in light duty engines

The diesel particulate filters (DPF) are considered the most robust technologies for particle emission reduction both in terms of mass and number. On the other hand, the increase of the backpressure in the exhaust system due to the accumulation of the particles in the filter walls leads to an increase of the engine fuel consumption and engine power reduction. To limit the filter loading, and the backpressure, a periodical regeneration is needed. Because of the growing interest about particle emission both in terms of mass, number and size, it appears important to monitor the evolution of the particle mass and number concentrations and size distribution during the regeneration of the DPFs. For this matter, in the presented work the regeneration of a catalyzed filter was fully analyzed. Particular attention was dedicated to the dynamic evolution both of the thermodynamic parameters and particle emissions. The measurements were performed at the exhaust of a Euro 5 CR Diesel engine equipped with a Close Coupled DPF. The regeneration process was investigated in a point representative of an extraurban engine operating condition. The regeneration was managed by the electronic control unit (ECU). In particular, an injection calibration was implemented taking into account the engine and the filter features. The particle size distribution evolution during regeneration phase was measured in the size range 5-1000 nm using a differential mobility spectrometer. The particle mass concentration was monitored by means of a microsoot sensor. Particle mass and number concentrations strongly increase during the regeneration process. Moreover, a high concentration of the number of particles smaller than 30nm was observed in some critical phases of the regeneration process.