Abstract. Cheap renewable fuels are needed to replace fossil fuels to reduce greenhouse gas emissions that are causing global warming with the attendant negative consequences. The properties of blends of spent groundnut oil methyl ester (SGOME) and fossil diesel and the emissions from these blends as engine fuel were determined. Spent groundnut oil (SGO) was transesterified into SGOME using methanol and potassium hydroxide as catalyst. The SGOME was blended with fossil diesel and the properties determined and compared to fossil diesel (B0). The pure SGOME (B100) was blended with 90%, 80%, 70%, 60%, and 50% diesel to obtain the B10, B20, B30, B40, and B50 blends of biodiesel, respectively. The properties of the SGOME and the blends were determined according to ASTM and AOCS standards for biodiesel. The properties determined were flash point, carbon residue after combustion, pour and cloud points, kinematic and dynamic viscosities. The blends were used as fuel in a single cylinder 4-stroke water-cooled compression ignition engine that was coupled to a dynamometer from which the tail pipe emissions were measured using gas analyzers. The emissions were measured after the engine had reached a steady state at no load (0 kW) and 1 kW at 3 min interval for 15 min for each blend in 3 replicates. The greenhouse gas emissions measured were nitrogen oxide (NOx),hydrogen sulphide (H2S), particulate matter (PM), sulphur dioxide(SO2),and carbon monoxide (CO). The analysis of variance (ANOVA) at p = 0.05 was used to determine if there was significant difference in the amount of gas emitted from the various blend fuels. The F-LSD was used to separate the means where there was significant difference. The higher blends of the SGOME had better flash point, pour point, and dynamic viscosity than the lower blends. However, the lower blends had better cloud point. The carbon residue after combustion of the SGOME blends was better than that of the fossil diesel. The NOx, PM, SO2, and CO emissions were significantly different from the various blends of the SGOME. However, the H2S emission was not significantly different. Loading the engine did not significantly affect the NOx, H2S, SO2, and CO emissions but significantly affected the PM emission. The PM, CO, and SO2 emissions were highest from the fossil diesel and the lower blends (B10, B20, and B30) and lowest from the higher blends (B40, B50, and B100) at both engine loads. The NOx emission was lowest from the fossil diesel and the lower blends. The use of B20 increased the NOx emission by 10% at both engine loads. The H2S emission was the same for the fossil diesel, pure SGOME (B100), and the blends (B10–B50) at both engine loads. The SGOME fuel reduced tail pipe emission of PM, CO, and SO2 by 26%, 45%, and 78%, respectively. The higher blends had a considerably lower amount of toxic emissions at both engine loads. Keywords: Blends, Diesel, Emissions, Engine, Fuel, Properties, Spent groundnut oil methyl ester.
