Optimization of a diesel engine calibration for operating with a residual glycerol-derived biofuel

Abstract

The new European directive for the promotion of renewable energy mandates an increase in the share of advanced and waste-based biofuels in the transport sector. In this study, an advanced glycerol-derived biofuel was used as a component of a ternary blend, denoted as o·bio^®. This blend included 27.4 %v/v of fatty acid glycerol formal ester, 69.6 %v/v of fatty acid methyl ester and 3 %v/v of acetals obtained as a by-product of the fatty acid glycerol formal ester production process (which were proved to improve cold-flow properties). Finally, o·bio^® was blended with diesel fuel at a content of 20 %v/v. Two operating conditions based on usual driving modes were selected, where the engine calibration could be re-optimized after the change of fuel, corresponding to vehicle velocities of 50 and 70 km/h. Since the main effect of the blend used is to reduce particulate matter emissions, exhaust gas recirculation was increased and injection was delayed, so that the initial benefits in particulate matter emissions could be re-distributed into benefits in both particulate matter and nitrogen oxides (NO_x) emissions. From a combined analysis of the particulate matter–NO_x trade-off and trying to limit the negative effect of delaying injection on fuel consumption, the final proposal was to set an additional 6% exhaust gas recirculation at 50 km/h and an additional 3% exhaust gas recirculation at 70 km/h, while delaying injection 2 °CA after top dead center at both vehicle operating conditions with respect to the original calibration. The use of the blend along with the optimization of the engine calibration is expected to reduce particulate matter and NO_x emissions by around 50% with a vehicle speed condition of 50 km/h and to reduce particulate matter and NO_x emissions by around 30% and 40% at 70 km/h with respect to diesel fuel emissions.