Two-dimensional measurements of primary soot diameter in diffusion flames by two-dimensional time resolved laser induced incandescence

Two dimensions primary soot diameter calculation in a laminar diffusion liquid petroleum gas flame by means of laser induced incandescence (LII) is presented in present paper. LII is a high sensitive technique in which a high energy Nd-Yag laser sheet heats soot particles up to a temperature of about 4000 K but without exceeding the sublimation temperature. Radiation from exited soot particles is acquired by means of an intensified coupled charge device (CCD) camera (low gate opening time of 10 ns) synchronised with the laser pulse. By delaying the acquisition time with respect to laser pulse, LII signal decay as function of time has been reconstructed. Performing acquisition at two different wavelengths by means of two interferometric filters (two colour LII) a soot temperature behaviour (related to particles primary diameter) has been calculated. For quantitative measurements of the soot volume fraction a tungsten lamp calibration method for optics was used. Using laser fluence and self-absorption corrections for LII signal, bi-dimensional quantitative measurements can be achieved for soot dimensions and distribution. By means of a flame centre-of-mass alignment on the corrected images for different time steps, it is possible to achieve the soot decay curve for each pixel of the images, performing a two-dimensional (2D) soot primary particles visualisation.