Long-Term Stability of B50 Biodiesel under Humid Tropical Storage Conditions: A Comparative Case Study of Conditioning Strategies

The long-term storage stability of high-blend biodiesel remains a critical operational challenge in tropical regions due to elevated temperature and humidity. This 36-week outdoor case study evaluated the storage behavior of B50 biodiesel under humid tropical conditions (22–42 °C, relative humidity 46–90%). Three commonly applied conditioning strategies—nitrogen (N 2 ) blanketing, addition of 1000 ppm butylated hydroxytoluene (BHT), and weekly multistage filtration—were evaluated and compared with conventional ventilated storage. The study further examines operational trade-offs between mechanical cleanliness and chemical stability using TOTOX-based oxidation kinetics, water content, and ISO 4406 cleanliness indicators. Weekly multistage filtration improved particulate cleanliness but increased the oxidation as indicated by higher TOTOX than the reference method. Nitrogen blanketing showed the most robust overall performance by maintaining oxidation stability (Rancimat induction period >37 h) and water content (356 ppm) within Indonesian and ASTM limits throughout storage, while achieving acceptable cleanliness for up to 28 weeks. In contrast, BHT effectively delayed TOTOX increase but failed to control moisture uptake, exceeding national water-content limits after four weeks. These results demonstrate that TOTOX-based oxidation control strategies alone do not ensure holistic storage stability under humid tropical conditions and emphasize the importance of limiting fuel–atmosphere interaction.