Spatially resolved measurements of soot volume fraction using laser-induced incandescence

Abstract

Laser-induced incandescence is used to obtain spatially resolved measurements of soot volume fraction in a laminar diffusion flame, in which comparisons with laser scattering/extinction data yield excellent agreement. In addition, the laser-induced incandescence signal is observed to involve a rapid rise in intensity followed by a relatively long (ca. 600 ns) decay period subsequent to the laser pulse, while the effect of laser fluence is manifest in nonlinear and near-saturated response of the laser-induced incandescence signal with the transition occurring at a laser fluence of approximately 1.2 × 10 8 W/cm 2. Spectral response of the laser-induced incandescence involves a continuous spectrum in the visible wavelength range due to the blackbody nature of the emission. Simultaneous measurements of laser-induced incandescence and light scattering yield encouraging results concerning the mean soot particle diameter and number concentration. Thus, laser-induced incandescence can be used as an instantaneous, spatially resolved diagnostic of soot volume fraction without the need for the conventional line-of-sight laser extinction method, while potential applications in two-dimensional imaging and simultaneous measurements of laser-induced incandescence and light-scattering to generate a complete soot property characterization are significant.