Soot Measurements in a Simulated Engine Exhaust Using Laser-Induced Incandescence

Abstract

Soot mass concentrations were measured with laser-induced incandescence (LII) in a non reacting flow. The behavior of the LII signal with respect to soot concentration, particle size, and temperature was isolated with the use of a controllable soot-generating device. This device can simulate a hot, low-soot-concentration environment similar to that of a jet engine exhaust. Reduction of interference signals and high detection sensitivity were achieved with the use of a Nd:YAG laser at its fundamental wavelength and broadband detection from 570 to ∼850 nm. The LII signals were nearly proportional to soot concentration over 4 orders of magnitude, with a soot detection limit of better than ∼1 part per trillion (∼2 μg/m 3 ). The detection setup was designed, according to a model of the LII process, to reduce dependence on local gas temperature and soot particle size. Experimental results agreed with the model predictions in terms of particle size dependence, and negligible temperature dependence (beyond gas density effects) was seen for gas temperatures from 70 to 300°C.