EN 15751:2025

• Abstract:

  This document specifies a test method for the determination of the oxidation stability of fuels for diesel engines at 110 °C, by means of measuring the induction period of the fuel up to 48 h. The method is applicable to fatty acid methyl esters (FAME) intended for the use as pure biofuel or as a blending component for diesel fuels, and to blends of FAME with diesel fuel containing 2 % (V/V) of FAME at minimum.; The precision of the test method has been developed for conventional diesel. This test method is applicable for paraffinic diesel fuels as specified in EN 15940, however, a separate precision statement for paraffinic diesel is not available.; NOTE 1 EN 14112 [1] describes a similar test method for the determination of the oxidation stability of pure fatty acid methyl esters (see the Introduction to this document). Additionally, EN 16568 [4] describes a similar test method for the determination of the oxidation stability of fuels for diesel engines at 120 °C, by means of measuring the induction period of the fuel up to 20 h. EN 16568 is applicable to blends of FAME with diesel fuel containing 2 % (V/V) of FAME at minimum. Other alternative test methods for the determination of the oxidation stability of distillate fuels are described in CEN/TR 17225 [5].; NOTE 2 For induction periods higher than 48 h the precision is not covered by the precision statement of this method. The limit values of the relevant fuel standards are well within the scope of this test method.; NOTE 3 The presence of cetane improver can reduce the oxidation stability determined by this test method. Limited studies with EHN (2-ethyl hexyl nitrate) indicated, however, that the stability is reduced to an extent which is within the reproducibility of the test method.; NOTE 4 For the purposes of this document, the term “% (V/V)” is used to represent the volume fraction (φ) of a material.

• Status: Published
• Publication Date: 13-May-2025
• ICS: 75.160.40 - Biofuels
• Technical Committee: CEN/TC 19 - Petroleum products, lubricants and related products
• Drafting Committee: CEN/TC 19/JWG 1 - Vegetable fats and oils and their by-products for use in automotive fuels (Joint working group with CEN/TC 307)
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 14-May-2025
• Due Date: 02-Jun-2025
• Completion Date: 14-May-2025
• Ref Project: SIST 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

• Replaces: EN 15751:2014 - Automotive fuels - Fatty acid methyl ester (FAME) fuel and blends with diesel fuel - Determination of oxidation stability by accelerated oxidation method
• Effective Date: 26-Feb-2023
• Refers: EN ISO 3171:1999 - Petroleum liquids - Automatic pipeline sampling (ISO 3171:1988)
• Effective Date: 28-Jan-2026
• Refers: EN ISO 3170:2025 - Hydrocarbon Liquids - Manual Sampling (ISO 3170:2025)
• Effective Date: 28-Jan-2026
• Referred By: EN 16709:2024 - Automotive fuels - High FAME diesel fuel (B20 and B30) - Requirements and test methods
• Effective Date: 28-Jan-2026
• Referred By: EN 15940:2023 - Automotive fuels - Paraffinic diesel fuel from synthesis or hydrotreatment - Requirements and test methods
• Effective Date: 28-Jan-2026
• Referred By: EN 590:2025 - Automotive fuels - Diesel - Requirements and test methods
• Effective Date: 28-Jan-2026
• Referred By: CEN/TS 15940:2012 - Automotive fuels - Paraffinic diesel fuel from synthesis or hydrotreatment - Requirements and test methods
• Effective Date: 28-Jan-2026
• Referred By: EN 16734:2022 - Automotive fuels - Automotive B10 diesel fuel - Requirements and test methods
• Effective Date: 28-Jan-2026
• Referred By: CEN/TR 17225:2018 - Fuels and biofuels - Assessment on oxidation stability determination methods for distillate fuels and blends thereof with fatty acid methyl esters (FAME)
• Effective Date: 28-Jan-2026
• Referred By: EN 590:2022 - Automotive fuels - Diesel - Requirements and test methods
• Effective Date: 28-Jan-2026

Overview

EN 15751:2025 (CEN) specifies an accelerated laboratory test to determine the oxidation stability of fatty acid methyl ester (FAME) fuels and FAME/diesel blends by measuring the induction period at 110 °C. The method records the time (expressed in hours) until a rapid increase in oxidation products is detected - up to 48 h - and is applicable to neat FAME used as biofuel and to blends containing at least 2 % (V/V) FAME. The procedure is intended for routine quality control, specification compliance and comparative stability assessment of biodiesel and diesel blends.

Key topics and requirements

• Test principle: Heated fuel is exposed to a purified air flow; volatile oxidation products are swept into water where conductivity increase (due to acidic products) marks the end of the induction period.
• Test conditions: Nominal test temperature 110 °C; induction period measurement up to 48 h. For induction periods above 48 h, precision is not covered by this standard.
• Applicability: Neat FAME and FAME/diesel blends (≥ 2 % V/V). Precision data were developed for conventional diesel; method is applicable to paraffinic diesel (EN 15940) though no separate precision statement exists.
• Apparatus & consumables: Includes reaction vessels, closed measurement cells (~150 ml), conductivity electrodes (0–300 µS/cm), gas membrane pump (flow ~10 ± 1 l/h), heating block (up to ~150 °C), molecular sieve air filter and data acquisition system. Examples of compatible instruments cited: Rancimat® and OSI® instruments.
• Sampling & preparation: Sampling per EN ISO 3170 / EN ISO 3171; use distilled/demineralized water and specified solvents/cleaning agents. Store samples in the dark and test promptly.
• Limitations & notes: Cetane improvers (e.g., EHN) can reduce measured stability but observed effects are within method reproducibility for limited studies.

Applications and users

• Quality control laboratories in biodiesel production, fuel blending and petrochemical industries.
• Automotive and engine manufacturers assessing fuel compatibility and long-term performance.
• Fuel standards organizations, certification bodies and regulators verifying compliance with fuel stability limits.
• Research labs comparing oxidation behavior of FAME feedstocks, additives or paraffinic diesel blends.

Practical benefits include fast, repeatable assessment of fuel oxidation tendency, support for shelf-life and specification decisions, and comparative testing of additive effects.

Related standards

• EN 14112 - similar method for pure methyl esters (origin of method adaptations)
• EN 16568 - oxidation stability at 120 °C (induction up to 20 h)
• EN 15940 - paraffinic diesel specifications
• EN ISO 3170 / EN ISO 3171 - sampling of petroleum liquids
• CEN/TR 17225 - background and alternative methods for distillate fuels

Keywords: EN 15751:2025, oxidation stability, FAME, fatty acid methyl ester, accelerated oxidation method, induction period, 110 °C, FAME/diesel blends, biodiesel testing.

SLOVENSKI STANDARD
01-julij-2025
Nadomešča:
SIST EN 15751:2014
Goriva za motorna vozila - Metilni estri maščobnih kislin (FAME) goriv in mešanice
z dizelskim gorivom - Ugotavljanje oksidativne stabilnosti z metodo pospešene
oksidacije pri 110 °C
Automotive fuels - Fatty acid methyl ester (FAME) fuel and blends with diesel fuel -
Determination of oxidation stability by accelerated oxidation method at 110 °C
Kraftstoffe - Fettsäure-Methylester (FAME) Kraftstoff und Mischungen mit Dieselkraftstoff
- Bestimmung der Oxidationsstabilität mit beschleunigtem Oxidationsverfahren bei 110
°C
Carburants pour automobiles - Esters méthyliques d'acides gras (EMAG) et mélanges
avec du gazole - Détermination de la stabilité à l'oxydation par méthode d'oxydation
accélérée à 110 °C
Ta slovenski standard je istoveten z: EN 15751:2025
ICS:
75.160.20 Tekoča goriva Liquid fuels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 15751
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2025
EUROPÄISCHE NORM
ICS 75.160.40 Supersedes EN 15751:2014
English Version
Automotive fuels - Fatty acid methyl ester (FAME) fuel and
blends with diesel fuel - Determination of oxidation
stability by accelerated oxidation method at 110 °C
Carburants pour automobiles - Esters méthyliques Kraftstoffe - Fettsäure-Methylester (FAME) Kraftstoff
d'acides gras (EMAG) et mélanges avec du gazole - und Mischungen mit Dieselkraftstoff - Bestimmung der
Détermination de la stabilité à l'oxydation par méthode Oxidationsstabilität mit beschleunigtem
d'oxydation accélérée à 110 °C Oxidationsverfahren bei 110 °C
This European Standard was approved by CEN on 7 April 2025.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 15751:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 6
5 Chemicals . 6
6 Apparatus . 6
7 Sampling . 8
8 Preparation of measurement . 9
8.1 Preparation of test sample . 9
8.2 Preparation of apparatus . 9
8.2.1 Cleaning procedure . 9
8.2.2 Temperature correction . 9
9 Measurement . 10
10 Calculation and evaluation . 14
10.1 Automatic evaluation . 14
10.2 Manual evaluation . 15
11 Expression of results . 15
12 Precision . 15
12.1 General. 15
12.2 Repeatability, r . 15
12.3 Reproducibility, R . 15
13 Test report . 16
Bibliography . 17

European foreword
This document (EN 15751:2025) has been prepared by Technical Committee CEN/TC 19 “Gaseous and
liquid fuels, lubricants and related products of petroleum, synthetic and biological origin”, the
secretariat of which is held by NEN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by November 2025, and conflicting national standards
shall be withdrawn at the latest by November 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 15751:2014.
This document has been improved by editorial changes to clarify the test procedure.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Introduction
This document is based on EN 14112 [1], which was specifically adapted for the determination of
oxidation stability of fatty acid methyl esters (FAME). This method had been developed under
CEN/TC 307 (Fats and oils). At the time of development, the method was applicable for FAME fuel
according to EN 14214 [2], but questions remained on the accuracy towards blends of FAME and diesel
fuel.
The modifications to EN 14112 as given in this document, allow application of this test method for
oxidation stability for pure FAME and diesel/FAME blends at various levels.
The goal was to have one single test method for FAME fuel, diesel/FAME blends and pure diesel fuels.
Although the modifications cover FAME fuel and diesel/FAME blends, CEN/TC 307 decided that it was
better to retain EN 14112 for methyl esters and publish a separate standard for all automotive fuel and
heating oil applications, as the use of 'diesel and diesel blends' falls out the scope of CEN/TC 307.
EN 15751 was originally developed to describe the oxidation stability of blends consisting of
conventional diesel fuel and FAME. FAME blends with paraffinic diesel fuel were not included into the
fuel matrix used to acquire precision data.
While developing specification EN 15940 [3] for paraffinic diesel fuel, three laboratories executed a
small test on neat paraffinic fuel and on 7 % (V/V) FAME blends based on products originating from
both Fischer-Tropsch synthesis and hydrotreatment processes. No indications were found that FAME
blends with paraffinic diesel fuel behave differently than blends consisting of conventional diesel fuel
and FAME.
The modifications required a new validation covering pure FAME, diesel/FAME blends and pure diesel
fuels which resulted in the fact that the method has a lower precision for pure petroleum-based diesel
fuels.
1 Scope
This document specifies a test method for the determination of the oxidation stability of fuels for diesel
engines at 110 °C, by means of measuring the induction period of the fuel up to 48 h. The method is
applicable to fatty acid methyl esters (FAME) intended for the use as pure biofuel or as a blending
component for diesel fuels, and to blends of FAME with diesel fuel containing 2 % (V/V) of FAME at
minimum.
The precision of the test method has been developed for conventional diesel. This test method is
applicable for paraffinic diesel fuels as specified in EN 15940, however, a separate precision statement
for paraffinic diesel is not available.
NOTE 1 EN 14112 [1] describes a similar test method for the determination of the oxidation stability of pure
fatty acid methyl esters (see the Introduction to this document). Additionally, EN 16568 [4] describes a similar
test method for the determination of the oxidation stability of fuels for diesel engines at 120 °C, by means of
measuring the induction period of the fuel up to 20 h. EN 16568 is applicable to blends of FAME with diesel fuel
containing 2 % (V/V) of FAME at minimum. Other alternative test methods for the determination of the oxidation
stability of distillate fuels are described in CEN/TR 17225 [5].
NOTE 2 For induction periods higher than 48 h the precision is not covered by the precision statement of this
method. The limit values of the relevant fuel standards are well within the scope of this test method.
NOTE 3 The presence of cetane improver can reduce the oxidation stability determined by this test method.
Limited studies with EHN (2-ethyl hexyl nitrate) indicated, however, that the stability is reduced to an extent
which is within the reproducibility of the test method.
NOTE 4 For the purposes of this document, the term “% (V/V)” is used to represent the volume fraction (φ) of a
material.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN ISO 3170, Petroleum liquids — Manual sampling (ISO 3170)
EN ISO 3171, Petroleum liquids — Automatic pipeline sampling (ISO 3171)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp/
— IEC Electropedia: available at https://www.electropedia.org/
3.1
induction period
time which passes between the moment when the measurement is started and the moment when the
formation of oxidation products begins to increase rapidly
3.2
oxidation stability
induction period determined according to the procedure specified in this European Standard, expressed
in hours
4 Principle
A stream of purified air is passed through the sample which has been heated to the target temperature
which is 110 °C in the usual application of the method. Volatile compounds are formed during the
oxidation process. They are passed together with the air into a flask containing demineralized or
distilled water and equipped with a conductivity electrode. The electrode is connected to a measuring
and recording device. It indicates the end of the induction period by rapid increase of the conductivity
due to the dissociation of volatile carboxylic acids produced during the oxidation process and absorbed
in the water. For more details on the background of the method, see CEN/TR 17225.
5 Chemicals
5.1 Distilled or demineralized water according to EN ISO 3696 [6].
5.2 Alkaline laboratory glass cleaning solution.
5.3 Ternary solvent mixture 1 + 1 + 1 (by volume), consisting of methanol/toluene/acetone, each
of recognized analytical grade.
5.4 2-Propanol of recognized analytical grade.
5.5 Thermo-stable oil, e.g. silicon oil.
6 Apparatus
Usual laboratory equipment and glassware, together with the following:
6.1 Device for the determination of oxidation stability, comprising the following parts (see
Figure 1 and Figure 2).
6.1.1 Air filter, comprising a tube fitted with filter paper at the ends and filled with a molecular sieve
(6.6), connected to the suction end of a pump.
6.1.2 Gas membrane pump, with an adjustable flow rate of (10 ± 1,0) l/h.
6.1.3 Reaction vessels of borosilicate glass, provided with a sealing cap. The sealing cap shall be
fitted with an air inlet and outlet tube.
The length of the reaction vessel depends on the measuring equipment and shall exceed the depth of
the oven by at least 130 mm, in order to reduce evaporation losses to a minimum by condensing,
volatile fuel components at the cold vessel walls outside the oven.
EXAMPLE Total length of the test tube for the Metrohm Rancimat 743 L = 250 mm, for the Omnion OSI
Instrument L = 300 mm.
...