Development of 2C-Scheimpflug planar laser-induced incandescence system for soot concentration measurement at exhaust of aero-engine model combustor

Precise and quantitative measurement of soot particle emission plays an essential role in accurately assessing the combustion performance of aero-engine combustors and infrared signature levels in aircraft exhausts. Among various intrusive or non-intrusive approaches for soot diagnostics, Laser-Induced Incandescence (LII) technique has been increasingly applied for soot concentration measurement in various combustion environments such as laminar flames and internal combustion engines due to its high spatial resolution and sensitivity. As for LII measurement in aero-engine combustors, however, it normally suffers from very limited optical accesses and often faces mandatory requirements of oblique imaging from a small backward angle. In this work, we demonstrate a Two-Color (2C) LII system that simultaneously captures LII signal images at two distinct wavelengths using a Scheimpflug imaging configuration. A projective transformation algorithm and image overlapping procedures were employed to spatially correct the raw Scheimpflug LII images. Performance validation of the developed 2C-Scheimpflug LII system was first conducted under specified conditions in a laminar C₂H₄/air McKenna flame. The obtained Soot Volume Fraction (SVF) level and its spatial distribution are in consistent with previous studies under identical flame conditions reported by other research groups. Finally, as a demonstration of engineering benchmark application, we applied the developed 2C-Scheimpflug LII system to measure SVF distribution in the cross-section plane perpendicular to the direction of flame propagation at the exhaust of a single-sector dual-swirl aero-engine model combustor. Transient soot production events were observed and characteristics of the SVF distribution were investigated. These experimental results suggest the feasibility of the 2C-Scheimpflug LII technique developed in this work for precise and quantitative measurements of soot concentration in practical environments.