Single-point thermometry in high-pressure, sooting, premixed combustion environments

We have performed nonintrusive thermometry in the burnt gases of rich, pres surized ethylene/air flames using a frequency measurement based on laser-in duced gratings. Light from a continuous-wave probe beam is coherently scatt ered from a thermal or electrostrictive grating induced by a pair of crosse d, pulsed pump beams. The measured Doppler shift of the signal beam is a fu nction of the local speed of sound from which a temperature can be extracte d. At equivalence ratios of 1.6, the transient grating temperature agreed w ith a corrected thermocouple temperature. At higher soot loading, it is nec essary to account for the change in local gas composition caused by soot pa rticle vaporization. Soot particles, acting as blackbody absorbers, were ob served to generate thermal gratings of diagnostic value.