Laser-Based Combustion and Trace-element Analysis

Doctoral thesis, 1997

Laser spectroscopy has been utilised as a tool for combustion diagnostics and sensitive trace-element analysis. In the field of combustion analysis, a characterisation of a CH4/N2 - O2/N2 counter-flow diffusion flame has been performed using Laser-Induced Fluorescence (LIF). An absolute density profile of NO in the flame has been obtained, with concentrations up to a few tens of ppm. Temperature measurements by LIF on NO have also been performed. OH profiles were measured by both fluorescence and emission. In the trace-element analysis part of this thesis, the Tl content in rivers and lakes in the Göteborg area have been assessed to the range of a few tens of ppt by LIF in a Graphite Furnace. The Pb and Al contents of aerosols from the Norwegian Arctic have been analysed by the same technique. By the use of the LEI technique in conjunction of a rod-flame atomiser, the content of Co, Cr, Mn and Ni in NH4F and NaF, used in the production of optical fibres, have been determined. The fundamental studies were concerned with a reassessment of branching ratios and Franck-Condon factors in NO. Vibrational and rotational collisional redistribution processes within excited states of NO and OH in a counter-flow diffusion flame were measured, where the rotational transfer in excited state of the OH molecule clearly demonstrates a ladder effect. High-lying Fe I energy levels were labelled using of a two-step laser-ionisation technique. The lifetimes of some atomic metastable states in flames have been determined. New methods for determination of the local stoichiometry in flames (by the use of atomic metastable states) and for the determination of the flow-velocity of a pre-mixed flame (using a flow-tagging technique) have been developed.