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Non-intrusive diagnostic techniques based on broadband (190-550 nm) extinction and scattering spectroscopy were applied to undiluted exhaust Common Rail (CR) diesel engine. The influence of engine speed and load on soot mass concentration, size distribution of emitted particles and NOx concentration was analysed. NOx concentration was evaluated by “in situ” ultraviolet-visible absorption measurements and compared with those obtained by conventional analyser. The extinction and scattering spectra were compared with those evaluated by the Lorenz-Mie model for spherical particles in order to retrieve the size, the number concentration of the emitted particles and particulate mass.

Spectroscopic measurement and high speed visualization were used in single cylinder, four-stroke DI diesel engine, optically accessible. It was equipped with a four valves head and fully flexible electronic controlled ‘Common Rail’ injection system. The effect of pilot and main injection on combustion process was evaluated. Mixing formation, autoignition and soot formation process were analyzed by broadband ultraviolet-visible flame emission spectroscopy and high-speed digital imaging. The autoignition phase occurred near the tip of the jet and was characterized by strong presence of OH radicals for both investigated conditions The presence of C2 and OH radicals strongly characterized CR diesel combustion process during soot formation and evolution. In particular, high presence of OH concentration for the whole process from the autoignition to the soot formation and successive phases contributes to lower soot levels.

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).