Experimental investigation of fuel properties and engine operation with natural and synthetic antioxidants added to biodiesel

yClove (CEO) and thyme (TEO) essential oils were added to a colza biodiesel-diesel blend (B20) as natural antioxidants, and butylated hydroxytoluene (BHT) was added as a synthetic antioxidant, at 3000 ppm concentration. Fuel properties, instrumental characterizations, engine performance, combustion characteristics, and emissions of the blends were analyzed. Fourier Transform Infrared Spectroscopy (FT-IR) spectra showed that the transmission intensities of samples increased with antioxidant addition. B20 and B20-antioxidant blends were subjected to engine tests under various loads and a fixed engine speed of 1500 rpm to determine the combustion, performance, and emissions. Engine tests revealed that antioxidants caused an increase in specific fuel consumption by 0.9-2.4% and a drop of 1.1-2.2% in thermal efficiency compared to B20. Antioxidants increased in hydrocarbons HC emission due to their oxidation-inhibitive nature, while they provided substantial improvements in smoke opacity and CO2 emission. BHT reduced NO emissions by 21% compared to B20 fuel without antioxidants. BHT was more successful in curbing NO emissions but caused an average increase in CO emissions of 3.68%. CEO-blended fuel offers better engine performance and emissions improvement than TEO-blended fuel.