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 an 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 NOx-soot tradeoff, 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.