Abstract

We have applied the photoacoustic and photo thermal deflection spectroscopies to combustion diagnostics for a measurement of such parameters as minority species concentrations, flow velocities, and local flame temperatures. A frequency-doubled flash-lamp-pumped dye laser is used to excite OH molecules produced in the combustion of hydrocarbons. The amplitudes of the photoacoustic and photothermal signals resulting from the absorption of dye-laser radiation by OH molecules yield OH concentrations. The width and shape of the photothermal signal depends on the thermal diffusion constant and the rate of forced convection and therefore yields both the flow velocity and the local temperature. On the other hand, a measurement of travel time of the photoacoustic signal yields the local temperature of the flame (via acoustic velocity) and the flow velocity of the medium. We have exploited these potentials of the photoacoustic and photothermal techniques in a flame environment. We have also extended these measurements to sooting flames by generating the signals on soot particles.

© 1985 Optical Society of America