Comparative study of the opacity tendency of alternative diesel fuels blended with gasoline

New combustion concepts in Diesel engines imply the use of more appropriate fuels for this type of combustion than traditional diesel fuel. Low Temperature Combustion (LTC), as Premixed Charge Compression Ignition (PCCI), Homogeneous Charge Compression Ignition (HCCI) or Reactivity Controlled Compression Ignition (RCCI) concepts, have begun to use Diesel-Gasoline blends because their low cetane number can reduce, simultaneously, NOx and soot emissions and also improve thermal efficiency. However, new cleaner fuels, alternative to conventional fossil Diesel can also be a solution. In this work, the sooting tendency of Diesel-Gasoline blends was compared to three binary alternative fuels blended with Gasoline: a Biodiesel, a Gas-To-Liquid (GTL) and a new renewable paraffinic fuel called Farnesane. The Oxygen Extended Sooting Index (OESI) was chosen as an appropriate parameter for opacity tendency comparison. Results show that, for the same Gasoline percentage, the sooting tendency scales as follows: Farnesane = GTL < Biodiesel < Diesel. However, as a function of Gasoline proportion, the sooting tendency of Diesel and Biodiesel blends decreases, the later very slightly, while the propensity to smoke of both paraffinic fuels increases. A set of ternary Diesel-Farnesane-Gasoline blends indicates that aromatic compounds are the most influential parameter on opacity tendency. Results obtained in this work and their comparison to literature engine tests ratify that a previous study of sooting tendency can be a valuable tool for a later engine testing design.