Correlation characteristics of laser-induced soot incandescence and flame luminosity in diesel spray combustion

Understanding of soot formation and oxidation processes in diesel spray flame is significantly limited when using laser-based measurement due to its low-frequency operation. With the help of the advanced high-speed camera technology, visualization of flame luminosity in the transient diesel spray combustion is readily realized. While both laser-induced incandescence (LII) and flame luminosity are believed to originate from soot in diesel spray combustion, the correlation of actual planar soot field and volume integrated flame luminosity is unknown. The current work was devoted to quantitatively characterize in detail the possible correlation existing between the laser-induced incandescence (LII) of soot signals and flame luminosity. Diesel spray test was performed using ULSD #2 fuel of different injection pressures spraying into ambient density of 25.4 kg/m3 under the ambient temperature of 900 K with 15% O2 environment. Simultaneous measurement of LII and high-speed flame luminosity was conducted. 2D-based and 3D-based image correlations were conducted by applying three-point Abel inversion and volumetric integration, respectively. A weak image correlation was recognized for the two imaging techniques. It was found that the presence of turbulence, acquisition wavelength and soot temperature distribution can affect the correlation results.