Laser diagnostics of flames, combustion products, and sprays

Recently, numerous laser-based diagnostic methods have been developed to probe sprays and combustion processes. These diagnostic probes encompass spontaneous Raman spectroscopy, coherent Raman spectroscopy, laser fluorescence and absorption for temperature and species concentration measurements; laser Doppler velocimetry for fluid flow measurements; and particle sizing and vapor concentration in sprays by numerous optical methods. Specific examples will be presented of species concentrations and temperatures in flames. These results have been compared to theoretical calculations for these properties and in many cases show excellent agreement between experiment and theory. Moreover, the spatial resolution offered by these laser techniques allows one to determine how a flame is changed by the presence of an adjacent cooled, metal wall. Two new Raman spectroscopic methods are also described for the direct spectroscopic measurements in a flame of atomic oxygen-an important radical in flame chemistry. Finally, a two-wavelength absorption/scattering measurment is described whereby vapor concentrations inside sprays may be measured. This technique has been applied to measuring the vapor concentration in an axisymmetric n-heptane fuel spray.