Pinewood Intermediate Pyrolysis Oil as a Marine Fuel Blend Component in Biodiesel/n-Butanol Formulations

This study investigates pinewood-derived intermediate pyrolysis oil as a renewable blend component in biodiesel/n-butanol formulations for marine-fuel-property screening. Two intermediate pyrolysis oils produced at 500 °C using solid residence times of 20 and 40 min were characterised and incorporated at 30 vol% into ternary blends with waste cooking oil biodiesel and n-butanol. Selected ISO 8217:2024 RF-grade values were used as property benchmarks rather than as a basis for conformity assessment. The blends showed kinematic viscosities at 40 °C of 7.50–8.40 mm2 s−1, densities at 15 °C of 914.8–927.8 kg m−3, flash points of 60–85 °C, calculated carbon aromaticity index values of 842.9–858.6, acid numbers of 2.02–2.15 mg KOH g−1, micro carbon residue values of 5.94–7.97 mass% and gross heat-of-combustion values of 35.74–37.11 MJ kg−1. Sulphur was below the instrumental detection limit, although a matrix-specific numerical limit was not documented. The blend water contents ranged from 2.36 to 3.19 vol% and exceeded the selected ISO 8217:2024 RF-grade benchmark values. Potential total sediment (TSP) values of 0.30–0.50 mass% exceeded the selected maximum of 0.10 mass%, identifying sediment after thermal ageing as a major formulation issue. The formulations remained macroscopically homogeneous for 48 h under refrigerated storage; however, long-term stability, full ISO 8217:2024 conformity and marine-engine suitability were not established. The results support further development of intermediate pyrolysis oil/biodiesel/n-butanol formulations while identifying water analysis, sediment control, component characterisation and long-term stability as key priorities.