Highly viscous fuels present combustion challenges due to poor atomization and consequent inefficient air-fuel mixture, however, due to the demand for cheap heating fuels; burner design and fuel properties are continually optimized to enhance their combustion and emission performance. In this study, used engine oil was drained from the sump of a compression ignition engine; the oil was pre-treated to remove particulate matter, water and ferromagnetic materials. The oil samples were then blended with diesel fuel at different volumetric proportions and were characterized according to ASTM standard. The fuel samples were then combusted using atomizing swirl waste oil burner; flame temperature and flame size were measured using infrared thermometer and direct photography respectively. The burner was then mounted to a combustion chamber and the emission gases and flue gas temperatures were measured using a flue gas analyser and digital thermometer respectively. It was revealed that increasing diesel fuel blend decreases the density and viscosity of the fuel samples. All the blended fuel samples were found to form a homogenous mixture and generated flame temperature higher than the unblended oil sample (B0), B20 generated the highest flame temperature of 1400 °C with flame size of 340 × 210 mm and the lowest carbon monoxide (CO) emission of 0.49 %, unburned hydrocarbon (HC) of 249 ppm and the highest carbon dioxide (CO2) of 12.87 % levels. In view of this, diesel fuel can be used as a good blending candidate to used engine oil to improve flame temperature and decrease emission levels in swirl waste oil burners.
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