Soot is an unwanted contaminant formed during technical combustion processes such as those occurring in internal combustion engines and aero engines. Its dangerous effects on human health and the global climate have long been known. It has been possible in recent years to reduce soot emissions dramatically, mainly with measures secondary to combustion itself (e.g. soot particle filters) and with technical measures that also result in reductions in particle size. However, smaller soot particles inhaled into the lung can seriously increase the risk to health. Research and development work is urgently needed in order to prevent the formation of soot during the actual combustion process itself.
Our contribution to current soot research consists in applying sophisticated laser measurement techniques to defined sooting flames to generate data which provide detailed insight into soot formation processes and therefore help to improve our understanding of soot formation. The early phase of soot formation during combustion plays a special role in this regard. In our work, we study the formation of primary soot particles in the gas phase depending on pressure, stoichiometry and the type of fuel.
A special high-pressure combustion chamber with optical access is used in which different burners can be installed. For fundamental investigations of the mechanisms of soot formation, a coflame burner for flat laminar flames is used while swirl burners are utilized for the study of turbulent gas turbine-relevant flames. In addition to the analysis of soot formation also the oxidation of soot can be investigated by the injection of secondary air into the combustion chamber. The soot concentrations in the flames are measured by laser-induced incandescence (LII), the flow velocities by particle image velocimetry (PIV) and the temperatures by coherent anti-Stokes Raman spectroscopy (CARS). Besides a better insight into the soot formation processes in flames the results also present an experimental data basis for the validation of chemical-kinetic reaction mechanisms and of numerical simulations.