Drop-In Capability of Solketal in Diesel and Gasoline Fuels Containing Biodiesel, HVO, Fossil Diesel, and Gasoline Based on Standard Physical and Chemical Fuel Properties

This study evaluates the drop-in capability of solketal in terms of the physical and chemical parameters defined for diesel and gasoline fuels. To this end, miscibility gaps revealed that solketal is immiscible with pure hydrocarbons and lower aromatic fossil diesel fuel (18.84 wt %), while biodiesel acts as an effective solubilizer due to its amphiphilic structure. Solketal exhibited a significant influence on fuel polarity, as demonstrated by increases in permittivity (ε) and decreases in interfacial tension (it) (in binary blends with biodiesel: 15.7% (ε) and 43.6% (it); in ternary alkane-biodiesel blends: 9.8% (ε) and 68.3% (it)). At 3 vol % solketal, Diesel R33 remained EN 590 compliant despite increased density and reduced ignition quality and flash point. Density increased by ∼0.9% per 5 vol % solketal in binary biodiesel blends and by 0.6-1.0% in ternary hydrotreated vegetable oil blends. At maximum solketal contents (20 vol % binary, 9 vol % ternary), cetane number decreased by up to 15% and 5.7%, respectively, while cetane index decreased by up to 60.7% in binary blends. The flash point decreased by up to 41% in binary and 2-6% in ternary blends. Pure solketal exhibited a vapor pressure 32-50 times lower than ethanol and methanol at 100 °C but increased biodiesel vapor pressure by a factor of 1.07 at 20 vol % blending, indicating nonideal behavior. In gasoline blends, vapor pressure decreased by only 8-11%, maintaining acceptable Reid vapor pressure.