Soot measurements in a simulated engine exhaust using laser-induced incandescence

Soot mass concentrations were measured with laser-induced incandescence (LI I) in a nonreacting how, The behavior of the LII signal with respect to soo t concentration, particle size, and temperature was isolated with the use o f a controllable soot-generating device. This device can simulate a hot, lo w soot concentration environment similar to that of a jet engine exhaust. R eduction of interference signals and high detection sensitivity were achiev ed with the use of a Nd:YAG laser at its fundamental wavelength and broadba nd detection from 570 to similar to 850 nm. The LII signals were nearly pro portional to soot concentration over 4 orders of magnitude, with a soot det ection limit of better than similar to 1 part per trillion (similar to 2 mu g/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 s ize. Experimental results agreed with the model predictions in terms of par ticle size dependence, and negligible temperature dependence (beyond gas de nsity effects) was seen for gas temperatures from 70 to 300 degrees C.