The development of laser-induced incandescence for quantitative measurement of soot volume fraction in flames

The development of lasers over the past several decades has greatly advanced the capability of measuring the properties and concentration of soot particles in a combustion environment. Until recently in-situ measurements have been limited to steady or time-averaged turbulent environments through laser light scattering (LLS) and extinction techniques. While the scattering signal is both spatially and temporally resolved, the extinction signal is neither. Temporal resolution is limited by a low signal-to-noise ratio and spatial resolution is limited because it is a line-of-sight measurement.; With the development of laser-induced incandescence (LII) and its strong correlation with soot volume fraction, the extinction portion of the scattering/extinction method can be replaced with a temporally and spatially resolved diagnostic. With a dual camera or dual imaging system, LII/LLS can be used to instantaneously image spatially resolved soot particle properties in two dimensions.; LII is a very new diagnostic technique that has not been well characterized by the small research community to embrace it so far. The present work advances our understanding of the phenomena known as laser-induced incandescence and lays out a systematic method for applying this highly useful diagnostic. Both theoretical and experimental studies of the primary parameters influencing the LII signal have been made, including laser intensity, signal gating, and collection wavelength.; The major conclusion of the work is that, with the proper choice of these parameters, the LII signal yields results which are favorably comparable to measurements obtained from extinction technique approaches. For our research we employed a frequency-doubled, 532nm beam from a Nd3+:YAG Q-Switched pulse laser. With this constraint, we determined that LII can accurately measure soot volume fraction by collecting LII over a narrow spectrum centered at 680nm and a 20 to 50ns prompt gate.; In addition, we developed several corrections to the LII signal which improve quantitative measurements. These include a correction for the extinction of the LII signal and corrections for variations in the laser sheet energy. Finally, we attempted to measure soot growth rate by employing a dual laser variation to the standard LII method but found that the results were not of the desired accuracy.