Effects of Neem Oil-Derived Biodiesel Addition to Diesel on the Reactivity and Characteristics of Combustion-Generated Soot

This study reports the impact of a biodiesel, produced from inedible neem oil through a transesterification process, on the formation and physicochemical properties of soot from diesel/biodiesel blends. A smoke point test for the diesel/biodiesel blends is presented that reveals a nonlinear reduction in the sooting propensity of diesel with increasing proportion of neem-biodiesel in the blends. Soot particles from the diffusion flames of pure diesel and a diesel/biodiesel blend are analyzed through thermogravimetric analysis, high-resolution transmission electron microscopy, electron energy loss spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy techniques. Soot from the blended fuel was found to be more reactive in air than that from pure diesel. To understand and explain the reactivity differences, the nanostructural changes (the sizes of aromatics and the primary particles comprising soot, and the thickness of the nanocrystallites) along with the variation in the chemical composition (the concentration of oxygenated functional groups, σ and π bonding, and the aliphatic and aromatic content) in soot arising from the addition of biodiesel to diesel are determined. The presence of neem-biodiesel in the fuel was found to enhance the concentrations of aliphatic and oxygenated groups on soot, possibly due to the high amounts of saturated fatty acid methyl esters and the presence of fuel-bound oxygen in it.