EN 14112 is the European test method for determining the oxidation stability of FAME biodiesel by accelerated oxidation at 110 °C — commonly called the Rancimat method. Air is bubbled through a heated fuel sample; volatile acids produced by oxidation are carried into a water cell where conductivity is measured. The time before conductivity rises sharply is the induction period, reported in hours. EN 14214 requires a minimum of 8 hours for B100.
The method is deceptively simple to describe and easy to run badly. Most disputed results trace back to sample handling rather than to the instrument.
How the method works
Principle. Oxidation of FAME proceeds through a radical chain. Initially, naturally present and added antioxidants intercept radicals and the reaction is suppressed — this is the induction period. Once antioxidants are consumed, oxidation accelerates rapidly, producing volatile short-chain carboxylic acids, principally formic and acetic acid. These are swept by the air stream into a measuring cell containing deionised water, where they dissociate and raise conductivity.
Conditions.
| Parameter | EN 14112 |
|---|---|
| Temperature | 110 °C |
| Air flow | 10 L/h |
| Sample size | 3 g |
| Measurement | Conductivity of the absorption water |
| Result | Induction period, hours |
| Applicability | FAME (B100) |
Determining the endpoint. The induction period is the intersection of the tangents to the conductivity curve before and after the inflection. Modern instruments compute this automatically as the second derivative maximum. Manual tangent construction on an ambiguous curve is a recognised source of operator-to-operator variation.
EN 14112 versus EN 15751 versus EN 16568
Three related methods exist, and using the wrong one produces a valid number against the wrong specification.
| Method | Applies to | Temperature | Max measurable | Referenced by |
|---|---|---|---|---|
| EN 14112 | FAME (B100) | 110 °C | — | EN 14214 (min 8 h) |
| EN 15751 | FAME and FAME/diesel blends ≥2% v/v | 110 °C | 48 h | EN 590 (min 20 h), also EN 14214 |
| EN 16568 | FAME/diesel blends ≥2% v/v | 120 °C | 20 h | Alternative blend method |
The critical distinction: EN 14112 is for neat FAME. EN 15751 handles blends. If you are testing B7 diesel, EN 14112 is not the applicable method — use EN 15751 against the EN 590 limit of 20 hours. EN 14214 permits either EN 14112 or EN 15751 for B100.
Note also that EN 15751 precision is not covered above 48 hours. Results reported as “>48 h” are outside the validated range.
What causes a low result
Feedstock
Unsaturation drives oxidation. Untreated baseline induction periods vary enormously:
- Palm, tallow, coconut (saturated): often above 8 hours untreated
- Rapeseed, high-oleic sunflower (monounsaturated): typically 4–8 hours
- Soybean, sunflower, used cooking oil (polyunsaturated): commonly 1–4 hours
Processing residuals
Several contaminants act as pro-oxidants or accelerate hydrolysis:
- Monoglycerides and free glycerol — promote water retention and degradation
- Residual methanol — affects flash point and can interfere with the test
- Free fatty acids (high acid value) — both a symptom and an accelerant
- Trace metals, especially copper and iron — powerful catalysts for radical initiation. Even single-digit ppm copper measurably shortens induction period. This is the case for metal deactivators alongside antioxidants.
- Water — promotes hydrolysis and microbial growth
Storage history
Induction period declines over time. FAME held warm, in contact with air, in a copper-containing system, or exposed to light will test lower than the same batch tested fresh. A sample drawn from the bottom of a tank that has been standing is not representative of the batch.
Sample handling — where most errors originate
The single largest source of unreliable results.
- Use amber glass. Light initiates oxidation. Clear bottles compromise the sample.
- Fill completely. Headspace air continues oxidising the sample in the bottle. A half-full bottle degrades measurably before it reaches the lab.
- Avoid metal contact. No copper, brass or bronze anywhere in the sampling train.
- Keep cool and dark. Refrigerate if there is any delay.
- Test promptly. Within days, not weeks. Record the interval — it is part of the result.
- Sample representatively. Draw from a circulated tank or at multiple depths, not from the bottom drain.
A batch that fails on the customer’s test and passes on yours has usually been handled differently, not measured differently.
How to pass — and by how much
Do not target the limit. Dosing to exactly 8.0 hours means the batch will fail somewhere in the supply chain, because induction period declines during storage and transport. Target 10–12 hours at despatch where extended storage is expected.
Establish a dose–response curve. Antioxidant response is non-linear and feedstock-specific. The first increment of antioxidant buys more hours than the second. The only way to set an economic treat rate is to test your own FAME across a dose range — typically 100, 250, 500 and 1,000 ppm — and read the curve.
Match the antioxidant to the feedstock. Phenolic antioxidants differ substantially in effectiveness per unit dose, broadly in line with the number of hydroxyl groups on the ring: pyrogallol and propyl gallate (three) generally outperform TBHQ (two), which generally outperforms BHT and BHA (one). The ordering is feedstock-dependent and the published literature is not unanimous, so treat it as a starting hypothesis rather than a selection rule. See biodiesel antioxidants and TBHQ as a fuel antioxidant.
Add antioxidant early. Antioxidants prevent oxidation; they do not reverse it. Once peroxides and oligomers have formed, dosing recovers far less than dosing the same fuel fresh. Treat at production, not at the point of failure.
Control trace metals. Where copper or iron contact is unavoidable, a metal deactivator chelates the catalytic species and protects the antioxidant package.
Interpreting a marginal result
An induction period between 8 and 10 hours warrants attention rather than celebration. Ask:
- How old is the sample, and how was it stored before testing?
- What is the acid value trend across recent batches? Rising acid value with falling induction period indicates progressive degradation.
- Is the monoglyceride content near the 0.70% limit?
- Has feedstock composition shifted?
- Is there metal contact anywhere in storage or transfer?
A single number tells you less than the trend across batches.
Frequently asked questions
What is EN 14112?
The European test method for oxidation stability of FAME biodiesel by accelerated oxidation (Rancimat) at 110 °C, reporting the induction period in hours.
What is the difference between EN 14112 and EN 15751?
EN 14112 applies to neat FAME. EN 15751 applies to FAME and to FAME/diesel blends containing at least 2% v/v FAME, and measures up to 48 hours. EN 590 references EN 15751 for finished diesel blends.
What is a good Rancimat value for biodiesel?
EN 14214 requires a minimum of 8 hours. For material facing extended storage, 10–12 hours at despatch provides margin against ageing.
How long does an EN 14112 test take?
As long as the induction period, plus setup — so a stable sample at 12 hours takes over 12 hours of instrument time. This is why the accelerated method exists at 110 °C rather than at ambient.
Can oxidation stability be restored once it has dropped?
Only partially. Antioxidants inhibit further oxidation but do not reverse degradation already present. Peroxides, acids and oligomers already formed remain. Early dosing is substantially more effective than remedial dosing.
Does cetane improver affect the Rancimat result?
It can. The presence of cetane improver such as 2-ethylhexyl nitrate is noted in the standard as capable of reducing the measured oxidation stability.
Where to go next
If your batches are passing marginally or failing intermittently, the answer is usually in the dose–response curve for your specific feedstock rather than in a higher blanket treat rate.
Rodanco’s laboratory runs oxidation stability screening and antioxidant dose–response testing on client FAME samples. Our biodiesel antioxidants and metal deactivators are selected against that data rather than from a catalogue.
See also EN 14214 explained and our renewables capability.
Rodanco B.V., Alkmaar, the Netherlands. In-house laboratory screening, field trials and technical service for fuel producers, blenders and refiners across Europe.
Related articles
References
- BS EN 15751:2025 — Automotive fuels. FAME fuel and blends with diesel fuel. Determination of oxidation stability by accelerated oxidation method at 110 °C. Scope: induction period up to 48 h; applicable to blends containing at least 2% (V/V) FAME; notes that cetane improver can reduce measured oxidation stability. https://www.en-standard.eu/bs-en-15751-2025-automotive-fuels-fatty-acid-methyl-ester-fame-fuel-and-blends-with-diesel-fuel-determination-of-oxidation-stability-by-accelerated-oxidation-method-at-110-c/
- ÖNORM EN 14214:2019 preview — 8 h minimum oxidation stability. ANSI Webstore. https://webstore.ansi.org/preview-pages/ON/preview_ONORM+EN+14214_2019.pdf
- Effect of Metal Contaminants and Antioxidants on the Oxidation Stability of Argemone mexicana Biodiesel. Waste and Biomass Valorization, Springer. https://link.springer.com/article/10.1007/s12649-019-00886-5
About this article
Written by the Rodanco technical team. Rodanco B.V. operates an in-house laboratory in Alkmaar, the Netherlands, running screening, compatibility testing and tailored formulation work, and a field service team conducting on-site trials and dosing optimisation across European and global energy markets.
Standards notice. Values quoted from CEN standards are given for guidance. Standards are periodically revised and national annexes differ. Always verify against the current published edition before contractual or specification use.
Last reviewed: August 2026