Application of Laser Techniques for Combustion Studies

Abstract: 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 7 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.