Scientific Experiences in Energy and Thermal Engineering

This study compares the effect of a biomass-derived catalyst (areca-husk activated carbon, hereafter termed the biocatalyst) and a synthetic catalyst (silica–alumina) on the combustion characteristics and heat transfer rate of crude coconut oil (CCO) droplets, a renewable fuel that is difficult to burn because of its high viscosity. Each catalyst was blended into CCO at 1, 2, and 3 ppm, and 0.001 mL droplets suspended at a K-type thermocouple junction were ignited by a Ni–Cr wire heated at 12 V. Flame evolution was recorded with a digital camera and temperature–time data with a data logger, with five repetitions per condition; the heat transfer rate was estimated from the measured temperature using Newton's law of cooling. The biocatalyst blends burned for 1.68–2.00 s and reached peak flame temperatures of about 700–720 °C and peak heat transfer rates of 0.94–0.96 W, whereas the synthetic-catalyst blends burned longer (1.92–2.16 s) but peaked lower, at about 650–665 °C and 0.87–0.88 W. The biocatalyst blends also had a lower kinematic viscosity (27.37–27.46 cSt) than the synthetic-catalyst blends (30.54–32.52 cSt). Within the range tested, the biocatalyst mainly accelerates and intensifies heat release, with 2 ppm giving its longest flame (2.00 s), while silica–alumina mainly prolongs and stabilises combustion, with 3 ppm giving the longest flame of all blends (2.16 s). These findings indicate that low-cost activated carbon from agricultural waste can be used to improve the ignitability of raw vegetable-oil fuels in burners and small-scale combustion systems, whereas silica–alumina is better suited where a steady, sustained flame is required.