Application of a Novel Uncollimated Light Extinction for Soot Concentration Measurement

The sensitivity of the light extinction technique for soot measurement using a collimated light source was limited by beam steering. The problem becomes more pronounced when the technique was applied to high-pressure flames. A novel optical system was designed and built using an uncollimated light source to mitigate the beam steering effect. Two-dimensional transmissivity images obtained in a laminar coflow ethylene diffusion flame at atmospheric pressure with the uncollimated light source were shown to be more resistant to beam steering compared to those with a collimated light extinction. Through Abel inversion the radially resolved soot volume fraction distributions at different heights with uncollimated and collimated light extinction were in good agreement. The transmissivity profiles with the uncollimated light source suffer much lower levels of noise low in the flame and just outside the flame sheet. This study found that the uncollimated light extinction is a more sensitive and effective technique for soot concentration measurement in laminar axisymmetric flames. This technique will be applied to laminar axisymmetric flames at elevated pressures in the next step.