In this study, the morphological characteristics of the soot samples collected from a Lycoming O-320 piston engine, PT6A-42 turboprop engine, and Rolls Royce Allison 250C20B turboshaft engine were examined using Raman spectroscopy. The results obtained in this study indicate that engine and fuel type have to a certain extent some influence on the morphological characteristics of the soot particles. The examination of the spectral bands obtained using a 2-band deconvolution model of Raman data characterised the soot samples as graphitic and carbonaceous. Lead (PbCrO4) and Iron (Fe2O3) compounds were observed, where the main band for the symmetric stretch between Cr and O is evident at 839 cm-1. Lead oxide (PbO) and vanadinite [Pb5(VO4)3Cl] were also identified. The statistical analysis of peak full-width at half-maximum (FWHM) showed a more graphitic character in the soot sample collected from the Lycoming O-320 piston engine compared to the other engines. The intensity ratios (ID/IG) and band positions of G-bands and D-bands indicated a highly ordered crystalline structure in the PT6A-42 turboprop engine and Rolls Royce Allison 250C20B turboshaft engine compared to the Lycoming O-320 piston engine. The Principal Component Analysis (PCA) study on the soot samples where the engine type, fuel, G-bands, D-bands, and ID/IG were used as input parameters indicated that engine type influences the morphology of soot particles.

Keywords: Soot, Morphology, Particulate Matter, FWHM, ID/IG, PCA, G-bands, D-bands, Raman Spectroscopy, Aircraft Engines