Integrated study on engine combustion, performance, and emission analysis with sustainability assessment of Schizochytrium-derived algal biodiesel blends in compression ignition engine

This study investigates the combustion, performance, and emission characteristics of biodiesel blends produced from Schizochytrium, a relatively underexplored third-generation marine microalga, in a single-cylinder, four-stroke compression-ignition engine. The biomass was cultivated in-house, and biodiesel was synthesised through a two-step transesterification process. Two blends, B20 and B50, were evaluated over engine speed from 1200-2400 rpm at constant 15 Nm load. At 1800 rpm, peak in-cylinder pressure decreased by 2.29% (B20) and 6.34% (B50), while the maximum heat release rate reduced by 2.15% and 6.08%, respectively, compared to diesel. The brake thermal efficiency showed marginal decline of 1.42% (B20) and 6.32% (B50), accompanied by increase in brake-specific fuel consumption by 3.48% and 9.15%. Exhaust gas temperature increased by 3.12% and 8.89%, respectively, indicating slightly advanced combustion. Emission results revealed significant reductions in unburned hydrocarbons (18.7–40.2%), carbon monoxide (6.5–26.1%), and particulate matter (6.5–14.8%), with minor increase in NOx emissions. HR-SEM analysis indicated fewer but larger particulate agglomerates, suggesting altered surface reactivity and metal distribution. Techno-economic, SWOT, and PEST evaluations identified production cost as the major constraint. Overall, B20 exhibited the most favourable balance between efficiency and emissions, establishing Schizochytrium-based biodiesel as a sustainable and technically feasible CI engine fuel.