Measurement of Soot Volume Fraction in Counterflow Diffusion Flames Up to 10 Atm Using Optical Diagnostics

Abstract

ABSTRACTCombustion pressure has an influence on formation and destruction of soot. The balance of these processes determines the net soot emissions. In this work, the soot volume fraction (fv) in ethylene air counterflow flames has been investigated at elevated pressures using laser-induced incandescence (LII) and two-dimensional line of sight attenuation (2D LOSA) measurements. Pressure has been varied from 3 to 7 atm for fv measurements using 2D LOSA whereas fv has been reported from 3 to 10 atm using LII. Above 7 atm, counterflow flames were not perfectly axisymmetric, and therefore LII has been used instead of 2D LOSA above 7 atm. The fuel mole fraction varied between 0.2 and 0.3. Attenuation of LII signal has been corrected using LOSA measurements. Planar laser-induced fluorescence was used to study the location of polycyclic aromatic hydrocarbons (PAHs) at 3 and 7 atm. Locations of various sizes of PAHs have been reported by detecting the fluorescence signal at ranges of wavelengths centered at 350, 400, 450 and 510 nm. fv measurements by 2D LOSA and LII showed a good agreement. The LII signal showed significant attenuation due to the optical density of the counterflow flames, which highlights the importance of correcting the LII signal before inferring the values of the soot volume fraction. An increase in pressure resulted in an increase of the soot volume fraction and the overlap of the PAH zones and soot zone increased at elevated pressures.