Effects of Camphor Oil Addition to Diesel on the Nanostructures and Oxidative Reactivity of Combustion-Generated Soot

Less viscous and low cetane (LVLC) fuels have emerged as the promising alternative fuels or additives to fossil fuels. Camphor oil is one such potential LVLC fuel currently under consideration. However, its sooting propensity and subsequent effects on soot nanostructure, when blended with diesel, are not well understood. In this work, the effects of camphor and camphor oil addition to diesel on the sooting propensity, soot oxidative reactivity, and chemical composition, structural disorders, and morphology of the soot particles are studied using a diffusion flame. The chemical and the microstructural changes in soot are investigated using several experimental techniques such as energy dispersive X-ray spectroscopy, high resolution transmission electron microscopy, Raman and electron energy loss spectroscopy, and powder X-ray diffraction, while the oxidative reactivity is studied using thermogravimetric analysis. The activation energies for O₂-induced soot oxidation during the initiation stage shows a significant reduction in its value with the addition of camphor and camphor oil to diesel, which were 220 kJ/mol for diesel soot, 175 kJ/mol for 5% camphor/95% diesel soot, and 150 kJ/mol for 10% camphor oil/90% diesel soot. The blending of camphor and camphor oil with diesel results in soot with smaller fringe length and primary particle diameter but increases the fringe tortuosity, the degree of crystal disorder, and the amounts of oxygen functionalities and aliphatics in soot. These physicochemical changes in soot are used to explain the observed trend of oxidative reactivity. This study successfully demonstrates the potential of terpenoid keto compounds with characteristic bicyclic ring structure in improving oxidative reactivity of combustion derived soots as desired in diesel particulate filter technologies.