Podocarpus falcatus as a next-generation biodiesel feedstock: comparative insights with Jatropha curcas on oil yield, production, properties, and spray behavior

Growing energy demand and volatile fossil fuel prices have intensified the search for sustainable alternatives, positioning biodiesel as a renewable option with properties similar to petroleum diesel. This review provides a systematic, side-by-side comparison of Podocarpus falcatus (PF) and Jatropha curcas (JC) as biodiesel feedstocks, evaluating oil yield, extraction efficiency, production methods, physicochemical fuel properties, and spray behavior in compression ignition engines. JC, widely studied for its favorable fuel characteristics, faces limitations including low drought tolerance, inconsistent oil yield, and poor oxidation stability, constraining its practical application. In contrast, PF, an underexplored indigenous African species, exhibits higher oil content (58.93% versus 51.7% for JC), superior drought resistance, and a fatty acid profile rich in monounsaturated compounds, enhancing cold flow properties, oxidation stability, and spray atomization performance. The review discusses six oil extraction methods traditional, mechanical, solvent, supercritical, ultrasound-assisted, and enzymatic highlighting trade-offs in cost, yield, and operational complexity, and identifies transesterification as the most efficient and economical biodiesel production route. By synthesizing dispersed experimental data on PF and benchmarking it against JC under comparable conditions, the review explicitly links fatty acid unsaturation to spray behavior, an aspect rarely addressed in feedstock-focused studies. Integrating agronomic resilience, processing requirements, and combustion-relevant spray characteristics with fuel quality metrics, this work demonstrates the technical and environmental potential of PF as a sustainable, next-generation biodiesel feedstock, addressing a clear gap in the literature and supporting informed selection of resilient and high-performance feedstocks for future CI engine applications.