Spatially and temporally resolved laser/optical diagnostics of combustion processes: From fundamentals to practical applications

Laser diagnostic techniques have for more than five decades been used for gaining a deepened understanding of various combustion processes. The main reason for this is the possibility of non-intrusive measurements of key combustion parameters, e.g. species concentrations, temperatures and velocities, with high spatial and temporal resolution. The present paper will describe some development of the techniques themselves, followed by applications of relevant diagnostic techniques for studies of combustion phenomena and then more applied activities often related to challenges in an industrial environment. The paper is not meant to be a complete review of the entire research field but rather a survey with a majority of the contributions from the author's laboratory. After a short introduction and background (including some historical remarks), some common laser diagnostic techniques will be briefly described. Then some emerging techniques will be described. The first such area to be covered will highlight the use and application of structured illumination through Frequency Recognition Algorithm for Multiple Exposures, FRAME, enabling high speed visualization, 3D imaging and multiple species detection using one standard laser/detector. Furthermore, single ended diagnostics using Scheimpflug LIDAR and backward lasing using short pulse Stimulated Emission will be described and exemplified. In the category of studies of combustion phenomena, the paper will focus on diagnostic challenges and applications when studying combustion of some renewable fuels; solid biomass, ammonia and metals. When studying these fuels, often species not so commonly encountered when using fossil fuels are of interest, e.g. alkali containing species, e.g. KOH, KCl as well as nitrogen bound species, e.g. NH, NH2. In the field of applied diagnostics, preferably in an industrial environment, examples will be given from IC engines, gas turbines as well as full-scale industrial furnaces. In these phenomenological and industrial applications laser-induced fluorescence, Raman scattering and thermographic phosphorescence were mainly utilized, with some examples of photo-fragmentation LIF as well as non-liner techniques, IR-DFWM and CARS. The paper is concluded with a summary and some thoughts about the future.