Performance evaluation of used edible oil as diesel fuel

Abstract

In this study, used vegetable oil was collected from restaurants and processed to biodiesel through transesterification. Various properties of the biodiesel were determined and compared to those of diesel. Biodiesel was then subjected to engine tests in order to evaluate its performance as compared to diesel. Variables in engine performance were monitored for diverse blends of biodiesel and diesel. The effect of preheating biodiesel on engine performance was also studied. The properties evaluated included: density, copper strip corrosion, viscosity, heat of combustion, cetane index, sulphur content, distillation and cloud point. The values of the properties were found to be within or varied slightly from the standard specifications in ASTM D 975 for diesel fuel. The engine performance was evaluated in terms of the Brake Specific Fuel Consumption (BSFC) and Brake Thermal Efficiency. The engine was initially run on diesel to establish basic performance characteristics. Engine tests were then carried out using biodiesel from used vegetable oils, biodiesel-diesel blends, biodiesel preheated to 35 and 47ºC, and a subsequent comparative analysis done of their performance. From the tests, the average Brake Specific Fuel Consumption (BSFC) of biodiesel was found to be higher than that of diesel by approximately 12%. The fuels were then blended volumetrically to 20 (BD20), 40 (BD40), 60 (BD60) and 80% (BD80) biodiesel levels. Because of the greater energy density and better viscous properties of diesel, the engine was capable of generating the lowest BSFC while running on the reference diesel fuel. A small difference in BSFC was observed with BD20 and BD40 blends. As for BD60 and BD80, due to the energy differences previously noted, they produced a much higher BSFC than diesel fuels. But in general, all blends showed a lower BSFC as compared to neat biodiesel. iii Neat biodiesel was then preheated to 35 and 47ºC. It was observed that preheating biodiesel from ambient conditions to 35ºC reduced the BSFC from 12 to 7.8 % above that of diesel. Results of this study show that used vegetable oils can be processed to biodiesel of acceptable quality and used as fuel or additive to diesel fuel for use in diesel engines.