Synchronized 100-kHz Planar Laser-Induced Fluorescence and Schlieren Imaging of High-Pressure Spray Flames

In this study, a state-of-the-art pulse burst-mode laser system (100-kHz) and a customized nano-second pulse light-emitting diode (LED) were utilized for planar laser-induced fluorescence (PLIF) and schlieren imaging on n-dodecane spray combustion. Simultaneous high-speed imaging of PLIF and schlieren provides detailed physics of its ignition and combustion processes. The 100-kHz PLIF measurements show formaldehyde (CH2O) propagating into the jet head with increasing intensity, while schlieren signals exhibit a noticeable reduction (softening effect), due to the moderate heat release by cool flame. Comparison of sequential images between single-injection events and ensemble-averaged data shows a pronounced agreement in the timing and structures of CH2O and polycyclic aromatic hydrocarbon (PAH), suggesting a high level of repeatability. Based on the schlieren measurements, the high-temperature ignition delay was measured, aligning with the pressure-based delay in the chamber. The current study utilized proper orthogonal decomposition (POD) to analyze experimental measurements, extracting qualitative information about coherent structures in CH2O and PAH. A comprehensive examination of the POD results will be provided and presented in the presentation.