Abstract

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 (I_D/I_G) 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 I_D/I_G were used as input parameters indicated that engine type influences the morphology of soot particles.

Key words: Soot, morphology, particulate matter, FWHM, I_D/I_G, principal component analysis (PCA), G-bands, D-bands, Raman spectroscopy, aircraft engines.