Effects of the addition of a high energy density fuel, adamantane to diesel on its cetane number, sooting propensity, and soot nanostructural properties

Soot particles, released during diesel combustion, adversely affect human health and the environment. Some studies suggest blending diesel with oxygenated fuels to reduce soot emissions, though it also reduces fuel economy and may produce new pollutants such as aldehydes. Another method to reduce soot could be to increase its reactivity by altering its physicochemical properties (e.g., introducing curvatures in its nanostructures) so that it oxidizes inside the engine or flame. In this direction, a cyclic high-density hydrocarbon fuel, adamantane is studied as an additive for diesel to determine its effect on cetane number, threshold sooting index, soot reactivity, and soot nanostructural properties. The addition of up to 6.75 wt% of adamantane in diesel significantly increased the smoke point of diesel from 18 to 29 mm (and threshold sooting index decreased by 44%), indicating a drastic drop in fuel sooting tendency. Adamantane addition in a small amount to diesel minimally affected the cetane number. To understand the impact of adamantane addition to diesel on the characteristics of soot particles, different techniques including TGA, HRTEM, XRD, EDX, and EELS were used. It is observed that adamantane enhances curvatures in soot nanostructures and reduces the size of fringes in soot and its aromatic content, and all of these property variations improve soot reactivity to improve its oxidation in flames or engines and reduce soot emission.