Measurement of diesel particulate matter concentration by means of cavity ringdown spectroscopy

Aim of this article is to evaluate cavity ringdown spectroscopy (CRDS) as a suitable technique for the measurement of particulate matter concentration in diesel exhaust. The second harmonic of a Nd:YAG laser was used for pulsed cavity ringdown measurements of the optical extinction of diesel particulate matter. The investigation was carried out at the exhaust of a single cylinder prototype engine, derived from the Euro IV version of FIAT 1.9 JTD M-Jet 16V. Several steady state test points were investigated, corresponding to low and medium load conditions in the European emission test schedule for light duty cars. Unconventional diesel combustion regimes, aimed to get lower flame temperatures and overcome the NO_x -soot trade off, have been also investigated. Optical measurements have been compared against two commercial devices: a standard smoke meter (AVL 415S) was used to measure the Particulate Matter (PM) concentration, while a photoacoustic soot sensor (AVL 483 Micro Soot Sensor) was used to infer the corresponding carbonaceous fraction.