In this study, borax decahydrate as a fuel additive was studied in a diesel single-cylinder engine. Borax decahydrate was dissolved in 500 ml of methanol, 5 gr, 15 g and 25 g, and methanol was added 10% to diesel fuel. To be 90% Diesel + 10% Methanol (D90M10) 90% Diesel 10% Methanol + 1 g Borax...