ABSTRACT
Aromatic hydrocarbons (AH) and polycyclic aromatic hydrocarbons (PAH) are considered to play a key role in the formation of soot during combustion of hydrocarbon fuels. They are potentially carcinogenic or even mutagenic agents and they are found to be present in the emission from different combustion devices, i.e., power plants and exhaust from automotive engines, mainly diesel engines. In the near future, health regulations applied to urban areas in particular will require the access to diagnostic tools, which enable monitoring and the control of production of PAH or of soot parti culates at very low concentration levels (ppm to ppb). There is also a funda mental interest in understanding the mechanisms involved in particle formation, where aromatic substances play an important role. This is true for basic combustion research but also for setting up physical models and calculation codes for, e.g., technical combustion systems as furnaces and engines. Optical diagnostics techniques have proven to be efficient in other fields for in-situ and online remote sensing. In this chapter the properties of the laser-induced emission with respect to temperature and laser radiation are reported and discussed, as well as the possibility to identify and quantify different species and their aggregation into particles. The state of develop ment in applying such optical techniques is quite different for PAH and for soot research. While for PAH more laboratory-related techniques are used, soot diagnostics is meanwhile feasible in technical combustion systems by utilizing a relatively new approach based on laser-induced incandescence (LII).
