Experimental Comparison of Animal- and Plant-Derived Neat Biodiesels for Small Marine Diesel Applications: Performance, Emissions, and Operational-Cycle Assessment

The maritime sector’s greenhouse gas reduction targets are increasing interest in sustainable fuels compatible with existing diesel engine infrastructure. In this study, pure biodiesel of animal origin (AN100), pure biodiesel of plant origin (VG100), and conventional diesel fuel were experimentally compared in a single-cylinder, direct-injection diesel engine under controlled load conditions relevant to small-scale marine diesel applications. Brake specific fuel consumption (BSFC), brake thermal efficiency (BTE), and CO, HC, CO2, and NOx emissions were measured at six different engine loads. The data obtained were transferred to a representative 90-min operating cycle to determine total fuel consumption and emissions. Compared to diesel, AN100 and VG100 reduced CO emissions by 44.3% and 55.5%, and HC emissions by 18.2% and 26.0%, respectively. In contrast, CO2 emissions increased by 36.2% and 31.3%, while NOx emissions increased by 59.6% and 67.3%. Total fuel consumption also increased by 15.4% and 9.0% for AN100 and VG100, respectively, while BTE decreased by 8.1% and 0.3%. The operation cycle results confirmed that feedstock selection affects cumulative fuel demand and emissions. VG100 provided higher energy conversion performance, while AN100 offered a more balanced emission profile due to lower NOx and CO2 increases. The results indicate that the appropriate biodiesel selection should be made by considering fuel economy, emission priorities, and NOx reduction requirements together.