Experimental and thermodynamic analysis of a compression ignition engine operating with straight soybean oil

This paper presents an experimental and thermodynamic analysis of a compression ignition engine with rated power of 14.7 kW, fueled with diesel oil, straight soybean oil, and blend of 50 % (v/v) soybean and diesel oils. The experimental work consisted in characterization of physical-chemical properties of the fuels and steady-state measurements of brake power, fuel consumption and exhaust gas emissions (CO, CO2 and NOx ) as function of engine speed. Thermodynamic analysis was carried out at 1,800 rpm. The results were evaluated applying analysis of variance and the Dunnett's test. The engine operation with soybean oil in comparison with diesel oil showed reduction in power, increase in fuel consumption, similar fuel conversion efficiency, exergetic efficiency and exergy destruction. Analysis at 1,800 rpm for operation with soybean oil revealed 33 % of exergetic efficiency, within 95 % of confidence level. The patterns of the emissions revealed the important effect of the increased ignition delay time of the straight vegetable oil. Therefore, although preheating was used to adjust the fuel properties to provide similar spray regimes, the blending with diesel oil had an important effect in reducing the ignition delay time.