Performance and emissions characteristics of castor oil biodiesel fuel blends

Highlights: • Castor oil biodiesel blends did not impact on engine thermal efficiency with relation to diesel. • Castor biodiesel NOx penalty correlated to the biodiesel iodine value. • The higher oxygen content of castor biodiesel did not improve PM emissions. • Castor oil biodiesel PM, HC and CO emissions were load dependent due to poor atomization. - Abstract: This article comprises a series of experiments dedicated to the investigation of the operational effects of castor oil methyl ester blending into mineral diesel. Fuel blends containing 10 and 20% of biodiesel in volume were analyzed in tests conducted with a turbocharged diesel engine operating at steady state conditions. Soybean oil biodiesel fuel blends where also tested in order to provide a baseline to the expected behavior of a low viscosity first generation biodiesel. Exhaust gas concentrations of nitrogen oxides (NOx), unburned hydrocarbons (HC), carbon monoxide (CO), and total particulate matter (PM) were taken into account. The obtained results indicate that despite its unfavorable spray related properties, the castor oil methyl ester (COME) did not impact on engine thermal efficiency when compared to diesel fuel. The effects of COME upon HC and CO emissions were load dependable indicating a compromise between fuel oxygen content and poor breakup and evaporation properties. Both soybean and castor biodiesel blending into fossil diesel continuously increased the NO_x emissions with penalties correlated to the iodine number: Castor biodiesel emitted less NO_x than its soybean counterpart. The improved oxygen content with relation to the soybean biodiesel did not affect the PM emissions of the castor blends. A similar abatement of PM emissions with relation to fossil diesel was obtained with the castor and soybean fuel blends at mid and high engine load modes. At low load conditions, higher levels of PM were emitted for castor biodiesel blends when compared to soybean blends and the reference fuel.