Chemical and Physical Characteristics of Organic Particulate Matter from Exhaust After-Treatment System of Euro 6 Diesel Engine Operating at Full Load

The current legislation does not take into account the limitation of sub 23 nm particles from engine. Nevertheless, the Common Rail Diesel engine emits a large number of nanoparticle, solid and volatiles, that are very dangerous for human health. In this contest, the challenge of the "dieper EU project" is to apply advanced technologies for exhaust after-treatment to existing diesel engines and to optimize the characteristics of a new generation of engines with regards to emissions, fuel consumption and drivability. Aim of the present paper is to provide useful information for the development of the after-treatment system that will have to fulfill Euro6 further steps. In order to characterize the chemical and physical nature of Particulate Matter emitted from Euro 6b Medium Duty diesel engine, the pollutants were collected and analyzed: from engine-out, downstream of the particulate filter (DPF), and at the exit of a selective catalytic reactor (SCR). An array of chemical, physical and spectroscopic techniques (Gas chromatography coupled with mass spectrometry (GC-MS), mobility analyzer, UV-visible absorption and fluorescence spectroscopy) was applied for characterizing the organic particulate matter (PM, constituted of polycyclic aromatic hydrocarbons (PAH), heavy aromatic compounds, soot) in the exhaust line. The engine was operated in full-load condition (100% of the accelerator pedal position, representing the best performance of the engine operation) at different engine speeds. Results showed that the abetment efficiency of soot after DPF and SCR systems, at all engine speeds, is very high (around 90% or more), as evaluated gravimetrically and by mobility analyzer, which discriminates also among the different dimensional ranges of particles. The DPF is more efficient at collecting <23nm than >23nm particles whereas in the SCR system particles are subjected to reactions which seem to support an agglomeration of particles, with beneficial effect on the harmfulness to human health. For PAH the abatement efficiency is lower with respect to soot, but it increases at higher engine speeds, when the concentration is much higher.