Combination of Laser- and Mass-Spectroscopic Techniques for the Investigation of Fuel-Rich Flames

Abstract

Soot is one of the most important pollutants originating from combustion. Despite recent advances in the measurement of size and composition of soot particles, their actual formation mechanism is still under debate. It depends on fuel, stoichiometry, temperature, flow conditions and the concentration of a large number of intermediate species. An adequate characterization of this complex reaction system generally requires the use of several complementary techniques.

In this article, we present measurements aiming to study reactions in fuel-rich flames using several complementary techniques. Only with a combination of optical and mass-spectrometric measurements, important features of the early polyaromatic hydrocarbon (PAH) and soot formation chemistry are accessible in detail. Three different techniques are combined to investigate one-dimensional laboratory flames on the same low-pressure burner and their respective merits are discussed: (i) cavity ring-down spectroscopy (CRDS) for the detection of small radicals and measurement of the temperature, (ii) mass spectrometry with electron-impact (EI) ionization in order to measure species with molecular weights up to m/e = 90, and (iii) mass spectrometry with resonantly-enhanced multi-photon ionization (REMPI) to distinguish isomers with masses up to m/e = 178. Measurements of this type may prove a valuable input to improve kinetic and combustion models.