Implementation of a new spectroscopic method to quantify aromatic species involved in the formation of soot particles in flames

Abstract

The formation of aromatics and polycyclic aromatic hydrocarbons (PAH) in flames is still questionable and needs quantitative experimental data to improve the comprehension of these processes. Although aromatics and PAH are considered as the main species involved in soot formation processes, their quantitative detection still remains difficult. Indeed, it requires very sensitive and robust experimental setups enabling their measurements under very low concentrations (ppm order) in sooting flames conditions. The objective of this work is to propose an alternative setup based on laser diagnostics to allow the possibility of some specific studies of aromatics and PAH compounds in an experimentally less complex manner than conventional methods. We have developed a novel experimental setup, based on calibrated laser induced fluorescence (LIF) inside an expanded free jet, to get quantitative measurements of aromatics compounds after their extraction by a microprobe. Indeed, in the supersonic jet, the spectral simplification due to the cooling allows a selective detection of such complex molecules and their quantification. The experimental set-up as well as the first measurements of the benzene molecule formed in low pressure methane flames are presented in details. Potential of the sensitivity of the method is highlighted by determining very low concentrations of benzene (1–10 ppm).