Soot Imaging in Turbine Exhaust Plumes Using Fibre-Laser-Induced Incandescence

In-situ measurements of chemical species in combustion processes is an area of major research interest, in particular in the aerospace industry where regulatory demands are placing increasing importance on the quantification of emissions and the development of more environmentally friendly gas turbine engines. A critical consideration in the development of cleaner engines is gaining an understanding of the distribution and volume of soot particles in the exhaust plume produced during operation. Non-intrusive Laser-Induced Incandescence (LII) has been demonstrated for measuring soot volume fraction along a single path in gas turbine exhaust plumes using 10ns pulse diode lasers at 1064nm wavelength. Building on this research there is an interest to investigate the application of long-pulsed LII, of the order of 100s of ns, using higher-power fibre-lasers, and integrating tomographic techniques with LII measurements to provide 2D images of soot volume fraction and distribution across the exhaust plume of a gas turbine engine.Auto-projection tomography has been applied to imaging the space-point distribution of chemical specific information in liquid subjects by exploiting optically-induced fluorescence. Optical Fluorescence Auto Projection Tomography (OFAPT) has been demonstrated to be a suitable technique for in-situ non-intrusive imaging of chemical species in hostile environments offering benefits over traditional methods, such as Planar Laser-Induced Fluorescence (PLIF), notably the requirement for only single plane optical access to the region of interest.This talk will discuss the challenges of using long-pulse LII with soot particles and outline how auto-projection tomography techniques, similar to OFAPT, can be applied to LII measurements to provide a soot imaging capability in gas turbine exhaust plumes.