Biodiesel and the FAME Transition
Countries across Southeast Asia, Europe, and Latin America are incorporating Fatty Acid Methyl Esters (FAME) into their diesel pools as part of renewable energy mandates and efforts to reduce dependence on fossil fuels. Indonesia has been particularly progressive in its biodiesel program, advancing from B20 through B50. FAME is produced by transesterification of vegetable oils (primarily palm oil in Indonesia) and offers lower net carbon emissions alongside domestic energy security benefits.
As blending mandates increase, the quality demands on FAME and its blends become more critical. Higher FAME content amplifies the chemical instability that is an inherent property of ester-based fuels, making oxidation control and filter blocking prevention essential at every point in the supply chain.
Why FAME Degrades Faster Than Petroleum Diesel
FAME molecules contain unsaturated carbon-carbon double bonds that are inherently reactive with oxygen. Petroleum diesel is relatively stable during storage, but FAME initiates and propagates oxidative chain reactions significantly faster, progressing through three stages:
FAME also absorbs significantly more water than petroleum diesel. Free water at the fuel-water interface creates conditions for microbial growth, which accelerates degradation further and introduces biological contamination into the fuel system.
Palm-based FAME and tropical storage: Indonesian B-series fuels are predominantly palm-derived, which gives them relatively good cold flow properties but shorter oxidation stability compared to some other feedstocks. Combined with high ambient temperatures in tropical storage, the degradation rate is faster. This making stabiliser treatment particularly important in the Indonesian supply chain.
Oxidation Stability Testing, the Rancimat Method
The Rancimat method is the primary standard for measuring the oxidation induction period of FAME and FAME-containing diesel blends:
- EN 14112 applies to pure FAME (B100), conducted at 110°C
- EN 15751 applies to FAME/diesel blends at ≥2% FAME content, also at 110°C
The Oxidation Induction Period (OIP) is the time in hours before conductivity rises sharply. This indicating that oxidation has accelerated beyond the stable phase.
Specification requirements:
- EN 14214 (pure FAME): minimum 8 hours induction period
- EN 590 (diesel with ≥2% FAME): minimum 20 hours IP per EN 15751
Freshly produced palm FAME typically achieves 4–8 hours naturally. After production, transport, and storage, this value falls. Properly formulated biodiesel stabilisers extend the induction period substantially above the specification floor. This provides margin against the degradation that occurs during transit and storage before the fuel reaches the end user.
Filter Blocking Tendency (FBT) Testing
Rancimat measures the tendency of fuel to oxidize; FBT measures the consequence. Whether that oxidation produces material that will block fuel filters in service. EN 16329 (formerly the basis of CEC F-111) is the standard method:
- A defined volume of fuel (typically 300–600 mL) is drawn through a calibrated glass fibre filter paper under controlled vacuum at 40°C
- Flow time for successive equal volumes is measured precisely
- The FBT ratio is calculated from the progressive change in flow time. A ratio above 2 indicates significant filter-blocking material is present
FBT is particularly sensitive to polymeric peroxides and oxidative oligomers that form in aged or thermally stressed FAME blends. These species may not fully precipitate in a sediment test but will deposit onto filter media under the slight pressure differential of a fuel filter. This causing progressive restriction and ultimately filter failure.
The relationship between Rancimat IP and FBT is not always direct: a fuel may pass Rancimat but fail FBT if it contains pre-formed polymeric species from prior oxidation events, or if the antioxidant package has been consumed without stabilising all degradation intermediates. Effective biodiesel stabilisers address both dimensions.
Specification note: EN 16329 FBT is included in the EN 590 diesel specification (Annex B) as an informative method, and is referenced in several national fuel quality frameworks as a quality indicator for FAME-containing diesel. It is increasingly used by terminal operators and quality assurance teams as a release criterion for high-FAME blends.
Applications
| Application | Key Risk | Stabiliser Approach |
|---|---|---|
| Terminal blending (B20–B50) | FAME oxidation during storage; FBT failure before delivery to end user | Stabiliser dosed at terminal during FAME blending; antioxidant and dispersant package matched to FAME content |
| Long-haul distribution | Extended transit time compounds oxidation; temperature cycling accelerates degradation | Stabiliser dose at dispatch; maintains Rancimat IP and FBT compliance through the distribution chain |
| Depot and reserve stock | Months of storage at ambient tropical temperatures; antioxidant depletion over time | Higher-performance antioxidant package; dose at receipt; periodic testing to verify specification compliance |
| Seasonal and strategic reserves | FAME blends with extended storage mandates where specification compliance must be demonstrated on drawdown | Full stabiliser package with confirmed Rancimat compliance; documentation for quality assurance |