Application of Laser Techniques for Combustion Studies

Författare

Marcus Aldén

Summary, in English

The aim for this work has been to increase the applicability of

laser spectroscopy techniques for studies of combustion processes,

both what regards in-flame experiments, exhaust-gas analysis

and remote sensing of the atmosphere.

Raman spectroscopy has been used for analysis of exhaust gases

from flames, model fires of wood and for inflame measurements.

Coherent anti-Stokes Raman Spectroscopy CARS, has been used for

detection of several flame constituents e.g. o2 , CO, H2o,

CH4 and H2 . Flame temperatures are measured using CARS

spectra from N2 molecules. The CARS technique has also been

used for simultaneous detection of several species e.g. N2/CO,

co2;o2 and CO/H2 . The applications of broadband rotational

CARS have also been demonstrated in non-flame gases, whereas

scanning rotational CARS has been used for flame experiments.

Laser-induced fluorescence LIF is especially attractive for

radical detection, and LIF spectra for several flame radicals are

presented, e.g. OH, CN, CH and c2 as well as relative

concentration profiles for different radicals as a function of

height above the burner.

Special emphasis has been paid to space-resolved detection of

radicals in flames, e.g. OH using a diode array detector. In a

refined experiment, both c2 and OH were spatially detected

using two laser systems.

Two-photon excitation is a rather new and fascinating approach

for detection of flame species that absorb in spectral regions

not accessible for laser sources. In this way oxygen atoms have

been detected in an acetylene/oxygen flame.

Closely connected to combustion studies using laser methods is

remote sensing of pollutants in the atmosphere using laser

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techniques. These techniques have been used for laboratory

experiments and in real-world measurements. E.g., NO has been

detected using long-path absorption, whereas remote detection of

Hg atoms has been performed using the dial technique.

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