Experimental and modelling characterization of nanometric particles at the exhaust of Common Rail Diesel engine

The innovations in diesel engines have increased the need for detailed information about the chemical and physical properties of emitted particles. In fact, particulate mass concentration was reduced considerably more than the particles' number concentration and, so, their size is smaller, in the nanometric range. In this article, the application of non-intrusive diagnostic techniques, based on broadband (190-500 nm) extinction and scattering spectroscopy, has allowed detection and evaluation in real time of the size and number concentration of the emitted particles, and particulate mass. The optical experimental data were retrieved, according to the Lorenz-Mie model for spherical particles, in order to evaluate the influence of load and Exhaust Gas Recirculation (EGR) on the size distribution of emitted particles. In particular, two EGR strategies were chosen: the first optimized to reduce particulate exhaust mass concentration, the other set to increase it to high levels typical of old generation diesel engines. The optical measurements showed that new diesel engines, in spite of a drastic reduction in the exhaust particulate mass concentration, caused the emission in the atmosphere of a high number concentration of carbonaceous nanoparticles.