Study on inversion of morphological parameters of soot aggregates in hydrocarbon flames

Abstract This study proposes an effective inversion method to detect the morphological characteristics of soot aggregates in hydrocarbon flames. Firstly, the imaging method is used to measure the distribution of soot aggregates absorption coefficients in flames. Then, the primary particle diameter, primary particle number and volume fraction of soot aggregates are retrieved from the detected absorption coefficients using the particle swarm optimization algorithm. Meanwhile, the thermophoretic sampling particle diagnostic-transmission electron microscopy (TSPD-TEM) technique and the generalized multi-particle Mie-solution theory is employed to verify the absorption coefficients detected by the imaging method and the retrieved morphological parameters of soot aggregates by the proposed inversion technique. The comparison results reveal a deviation below 30% in absorption coefficients between obtained by the imaging method and the TSPD-TEM analysis combined with the generalized multi-particle Mie-solution theory. And the morphological parameters of soot aggregates retrieved using the inversion method are in good agreement with that obtained by the TSPD-TEM technique, which suggests that the inversion method is robust and can accurately retrieve the morphological parameters. Finally the distributions of primary particle diameter, primary particle number and volume fraction in flames for two different cases are presented, and effect of combustion condition and soot formation mechanism on the distribution rules of these morphological parameters is discussed. The proposed inversion method can provide detailed morphological information about soot aggregates for a deeper understanding and control of soot formation.