A calibration-independent laser-induced incandescence technique for soot measurement by detecting absolute light intensity

TLDR

Laser‑induced incandescence (LII) is a widely used diagnostic for spatially and temporally resolved soot volume fraction and primary particle size in flames and engine exhausts. The authors introduce a calibration‑independent LII method that determines soot volume fraction from the absolute incandescence intensity, eliminating the need for ex situ calibration with known‑fraction particles. The technique calibrates the detector’s spectral sensitivity using a known radiance source, then interprets the measured absolute intensity—requiring soot temperature from a model or dual‑wavelength measurement—to compute soot volume fraction. The method extends existing LII capabilities for practical quantitative soot measurements and is demonstrated in a laminar diffusion flame.

Abstract

Laser-induced incandescence (LII) has proved to be a useful diagnostic tool for spatially and temporally resolved measurement of particulate (soot) volume fraction and primary particle size in a wide range of applications, such as steady flames, flickering flames, and Diesel engine exhausts. We present a novel LII technique for the determination of soot volume fraction by measuring the absolute incandescence intensity, avoiding the need for ex situ calibration that typically uses a source of particles with known soot volume fraction. The technique developed in this study further extends the capabilities of existing LII for making practical quantitative measurements of soot. The spectral sensitivity of the detection system is determined by calibrating with an extended source of known radiance, and this sensitivity is then used to interpret the measured LII signals. Although it requires knowledge of the soot temperature, either from a numerical model of soot particle heating or experimentally determined by detecting LII signals at two different wavelengths, this technique offers a calibration-independent procedure for measuring soot volume fraction. Application of this technique to soot concentration measurements is demonstrated in a laminar diffusion flame.