Optical Diagnostic Techniques Applied in Practical Combustion Devices and Processes

Abstract: Optical measurement techniques have proven to be useful tools for studying combustion-related phenomenon. The fact that the techniques are optical facilitates performing the measurements without impinging upon the measurement object, such as the combustion event that can be involved. Such techniques can be species-specific and be performed in situ, i.e. in the setting in which the phenomena in question actually occur. The thesis also deals with the different types of equipment that can be taken advantage of and methods that can be employed to achieve measurements that are called for, as well as the basic theories behind the analyze that are performed. The thesis is structured, in brief, as follows:After the introduction, in which the need of combustion-related research is emphasized, important equipment and the basic principles behind its use are considered. In order to perform optical diagnostics, a light source of some sort is required. The chapter concerned with equipment is then introduced with information regarding the lasers employed in the thesis work. To be able to detect any signal induced by the light source involved, a suitable detector is needed. The basic principles of the different detectors employed are taken up, and the different measurement objects that the optical diagnostic techniques have been applied to, i.e. the laboratory combustors and the optical engines involved, are discussed. After measurements have been performed, the digital information acquired needs to be processed and analyzed. The information obtained is dealt with in post-processing steps, as they are called. Accordingly, basic knowledge of the tools employed in the image-post-processing work carried out is provided. The Equipment chapter concludes with a discussion of some sort of the basic theories behind various statistical quantities that can be involved in the post-processing of the data that has been collected.In order to draw adequate conclusions on the basis of the data that has been obtained and analyzed, comprehensive knowledge of the underlying theories connected with the methods employed, including those for inducing the signals that were detected, is of central importance. Theories behind the detection techniques employed – in particular those of Laser-induced fluorescence, Laser Doppler anemometry, Particle image velocimetry, Chemiluminescence and Rayleigh scattering – are taken up. The Methods chapter concludes with a discussion, in particular, of the lengthscales and various combustion regimes that can be distinguished, in turbulent flames, and certain theories connected with these.In the chapters thereafter what has been achieved with the tools and methods that have been employed, is discussed, the work as a whole is summarized and possibilities for further work in the area in question is considered.