Performance characteristics of a diesel engine run on biodiesel fuel and blends

Literature is replete with much research on the performance of biodiesel blends with petroleum in a diesel engine. Much of the researches did not consider the effect of biodiesel-biodiesel blends and injection system modifications on engine performance. The focus of this work is to examine the performance of biodiesels of Ghanaian origin namely Palm Kernel biodiesel (PKOME), Jatropha biodiesel (JCME), Coconut biodiesel (COME) and their biodiesel-biodiesel blends in a VW, four-cylinder, four-stroke, indirect injection engine which is turbocharged and air cooled. The combined effect of injection timing and pressure on engine performance are also investigated and their results compared with petroleum diesel results. Torque, brake power, brake specific fuel consumptions and brake thermal efficiencies were recorded for each fuel tested at varying engine speeds on an eddy current dynamometer. Petroleum diesel recorded at least 5% higher brake power and torque than biodiesel at all engine speeds. Brake specific fuel consumption of petroleum diesel was found to be 5% lower than biodiesel at all engine speeds. At initial engine speeds, biodiesel recorded higher thermal efficiencies of about 39% compared with petroleum diesel of 38% at 1800 rpm. Engine modifications were carried out for each fuel used except petroleum diesel. The input factors for the modification include injection timing only, injection pressure only and their combined effects on brake specific energy consumption and exhaust emissions particularly Carbon monoxide, Hydrocarbons and oxides of Nitrogen were investigated. Injection timing was varied at six (6) levels including advance of 9 0, 6 0, 3 0 settings and retardation settings of 6 0 and 3 0 while the engine default timing settings was kept at 0 0. Injection pressure in increments of 25 bars in the range of 150 bars to 250 bars was used. Generally, higher fuel injection pressures produced lower fuel consumption. For PKOME and COME, fuel injection pressure of 250 bars and an advance timing of 30 were found to have the lowest fuel economy and least tail pipe emissions. The optimal values for JCME were found to be at a pressure of injection of 200 bar and an advance timing of 30. PKOME and COME were blended in proportions of 100%, 75%, 50% and 25% by volume to determine the best blend for improved physiochemical properties for enhanced engine performance. JCME was also blended with COME in the same proportions by volume. In terms of exhaust emissions and fuel consumption, the optimum values were obtained with 75% COME and 25% PKOME by volume. Brake specific energy consumption (BSEC) of 15.4 MJ/kWh and emission values of CO = 0.39 Vol. %, HC = 45 ppm and NOx = 146 ppm was obtained. The optimum blend of JCME and COME was in the proportion of 75% JCME and 25% COME by volume. This also yielded BSEC of 13 MJ/kW-h, CO of 0.24 Vol. %, HC of 65 ppm and NOx emissions of 256 ppm, respectively. Petroleum diesel engine runs recorded BSEC of 11.8 MJ/kW-h, CO of 0.43 Vol. %, HC of 103 ppm and NOx of 140 ppm. Both BSEC and emissions were improved when biodiesels were blended with each other. Emissions of petroleum diesel such as Carbon monoxide and Hydrocarbons were 80 % and 50 % respectively higher than that of the best biodiesel-biodiesel blend by volume. Engine runs of PKOME-JCME blends were not conducted because JCME and COME feedstocks have very similar properties.

Source: KNUST