Marula Oil and Petrodiesel: A Comparative Performance Analysis on a Variable Compression Ignition Engine

Abstract

The quest for biofuel production and use in Botswana is driven by factors including volatile oil prices, need for fuel security, potential for job creation, potential reduction in greenhouse gas emissions, and economic diversification. In line with national efforts to come up with energy sources that are both environmentally friendly and sustainable, this work was carried out to compare performance properties of native crude marula (Sclerocarya birrea) seed oil and petrodiesel fuel on a variable compression engine test rig with automatic data acquisition set up. Parameters such as engine torque, brake power and specific fuel consumption were measured at different loads for the two fuels. The results indicate that engine performance when powered with crude marula oil compares favourable with those for petrodiesel. Optimum numerical values for engine torque, brake power and specific fuel consumption were 28.2 Nm, 6.27 W and 0.34 g/kWh respectively for petrodiesel, and 22.7 Nm, 6.6 W, 0.33 g/kWh respectively for crude marula oil. The engine performance was also analysed for same parameters, namely, engine torque, brake power and specific fuel consumption when powered using the same fuels over a range of compression ratios while the load was fixed at 80%. Optimum numerical values for engine torque, brake power and specific fuel consumption were 27.2 Nm, 3.67 W and 0.59 g/kWh respectively for petrodiesel, and 26.3 Nm, 3.6 W, 0.34 g/kWh respectively for crude marula oil. The results indicate that compression ratio of 16:1 yields optimum engine performance in terms of engine torque and brake power for both fuels under review. However, marula oil fuel recorded smooth steady increase in performance profile across all compression ratios which out-performs petrodiesel on lower compression ratios for engine torque and brake power, and is largely better than petrodiesel on fuel consumption.