Methods and systems relate to treating an oil-in-water emulsion with an electron beam to decrease aromatic content therein for subsequent recovery of diesel products with upgraded cetane number. The method includes passing the emulsion formed of water and a hydrocarbon stream, such as light cycle oil, through an electron beam. The electron beam causes radiolysis of the water into intermediates that react with and open rings of aromatic compounds from the hydrocarbon stream. Separation of the water from the emulsion after the treating with the electron beam provides the diesel products, which may be hydroprocessed to remove oxygenates.