Sustainable Essential Oil-Based Bioadditives for B35 Biodiesel Blends: Impacts on Fuel Quality, Engine Performance, and Emissions

The nationwide implementation of B35 biodiesel in Indonesia is constrained by elevated water and particulate contents, which accelerate fuel degradation and promote filter clogging. Mitigating these issues is essential to ensure fuel quality, safe distribution, and stable engine operation. This study proposes a renewable essential-oil-derived bioadditive as an alternative to petroleum-based additives, with novelty arising from a fractionation-guided multi-essential-oil formulation and its comprehensive validation, encompassing molecular characterization, fuel-quality compliance, engine performance, and exhaust emissions. The objective of this study was to develop and validate an essential-oil bioadditive capable of (i) reducing water and particulate contents in B35 biodiesel in compliance with Indonesian fuel standards and (ii) evaluating its effects on engine performance and emissions. Turpentine, clove terpene, citronella, and rhodinol oils were characterized by GC–MS and fractionated to obtain α-pinene-, caryophyllene-, and rhodinol-rich fractions. Eight formulations were prepared by varying oil ratios and blended into B35 at 0.1% v/v. Water content was monitored over 7 days of storage, followed by flash point screening. The optimal formulation was further evaluated for particulate content, physicochemical properties, engine performance using a dynotest, and exhaust emissions on a Kubota D722 diesel engine. Among all formulations, D1 (turpentine:clove terpene:citronella = 1:8:1) exhibited the most balanced performance. D1 reduced water content to 320 mg/kg, meeting the ≤400 mg/kg limit, and increased the flash point to 75 °C (minimum requirement: 52 °C). Particulate levels across 4, 6, and 14 μm fractions were substantially reduced. The B35 + D1 blend satisfied key fuel specifications, including a cetane number of 54.7, viscosity of 3.171 mm2/s, and oxidation stability exceeding 35 h. Engine testing showed more stable torque and power at high speeds with D1 at 1% v/v compared with 0.1% v/v. Smoke emissions decreased markedly, while NOx emissions increased, indicating a combustion trade-off typical of oxygenated additives.