Spray characteristics of emulsified castor biodiesel on engine emissions and deposit formation

摘要

Castor plants are a common wild poisonous plant in Asia, and especially a weed seen across Taiwan. Due to its high viscosity and water content, straight castor oil cannot be used as a fuel for DI engine. Transesterification and emulsion technologies have been utilized to improve the spray characteristics of castor oil. Without heat, the castor biodiesel (CBD) completes the transesterification reaction under ambient temperature. Gas chromatography indicates that the CBD yield rate is 97% or above. After long-term biodiesel generator test, the emulsified castor biodiesel (EBD) leads to the problem of engine deposition. Thus, this study aimed to investigate the EBD spray characteristics on DI engine emission and deposit formation. A constant-volume bomb was established to analyze the biodiesel spray characteristics under elevated temperature. A biofuel deposit simulator was developed to solve the EBD deposit problem. Thermal gravimetric analysis, Fourier transformation infrared spectroscopy, and scanning electron microscope were utilized to analyze the EBD deposit formation mechanisms. The experimental results indicated that biodiesel generator operated on EBD can improve the fossil diesel emissions. The high NOx emission of CBD was solved by water-biodiesel emulsion technology. The biofuel deposit simulator provided some potential deposit control additives for EBD during the laboratory research stage. Without changing the engine structure, when the injection pressure was increased by 5-10%, the optimum combination was 82.8% of castor biodiesel, 15% of water, 2% of bioethanol, and 0.2% of composite surfactant Span-Tween.