Parametric study of using transesterified biodiesel in a diesel engine

Abstract

The spray comparative tests on diesel/biodiesel–ethanol blends revealed that the spray tip penetration increases by a range from 4.4 to 21.5%, while the spray cone angle decreases by a range between 33.2 and 50.0% upon switching from diesel to biodiesel. Using biodiesel has an impact on the spray angle that is stronger than that on the penetration length. It was found that in order to minimize the relative reduction in the spray angle upon using a 50% petroleum diesel/50% biodiesel blend (B50), injectors of larger spray angles should be used, while no significant changes were found by adding ethanol to the diesel/biodiesel blends. The emission tests on a single cylinder naturally aspirated direct injection diesel engine showed that although the brake-specific fuel consumption (BSFC) increased upon switching from diesel to biodiesel, the unburnt hydrocarbons (HC) and carbon monoxide (CO) emissions decreased. Upon blending ethanol with the diesel/biodiesel mixture, the HC emissions decreased by a relative percent as high as 26.6%, while the percentage of decrease in CO reached 10.8% by increasing the injection pressure from 55 to 95 MPa. Adding biodiesel to diesel increased the nitrogen oxide (NOx) emissions due to the increased oxygen availability. Upon approaching the full load, the correspondingly reduced ignition delay resulted in earlier combustion and higher peak temperatures where an average turbulent kinetic energy of about 320 m2/s2 has been predicted. The NOx emissions were effectively reduced upon adding ethanol to the diesel/biodiesel blend due to the higher latent heat of evaporation of ethanol. Combining the retardation in the injection timing from −25 to −5° crank angle with the exhaust gas recirculation of 15% effectively reduced the NOx emissions to be below 2.6 g/kW.h.