SIST-TP CEN/TR 17225:2018
(Main)Fuels and biofuels - Assessment on oxidation stability determination methods for distillate fuels and blends thereof with fatty acid methyl esters (FAME)
Fuels and biofuels - Assessment on oxidation stability determination methods for distillate fuels and blends thereof with fatty acid methyl esters (FAME)
This document presents an overview of existing oxidation stability determination methods is provided, with an emphasis on differences between the Rancimat (EN 14112/EN 15751) and PetroOxy (EN 16091) tests.
Mitteldestillatkraft- und -brennstoffe und Biokraftstoffe - Bewertung der Verfahren zur Oxidationsstabilitätsbestimmung für Mittteldestillatkraft- und -brennstoffe und deren Mischungen mit Fettsäure-Methylestern (FAME)
Carburants et biocarburant - Assessment des méthodes determinations de la stabilité à l'oxydation pour distillats et mélanges avec esters méthyliques d'acides gras (EMAG)
Goriva in biogoriva - Ocenjevanje metod določevanja oksidacijske stabilnosti za destilatna goriva in njihove mešanice z metil estri maščobnih kislin (FAME)
Ta dokument podaja pregled obstoječih metod za določevanje oksidacijske stabilnosti s poudarkom na razlikah med preskusoma Rancimat (EN 14112/EN 15751) in PetroOxy (EN 16091).
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TP CEN/TR 17225:2018
01-december-2018
*RULYDLQELRJRULYD2FHQMHYDQMHPHWRGGRORþHYDQMDRNVLGDFLMVNHVWDELOQRVWL]D
GHVWLODWQDJRULYDLQQMLKRYHPHãDQLFH]PHWLOHVWULPDãþREQLKNLVOLQ )$0(
Fuels and biofuels - Assessment on oxidation stability determination methods for
distillate fuels and blends thereof with fatty acid methyl esters (FAME)
Mitteldestillatkraft- und -brennstoffe und Biokraftstoffe - Bewertung der Verfahren zur
Oxidationsstabilitätsbestimmung für Mittteldestillatkraft- und -brennstoffe und deren
Mischungen mit Fettsäure-Methylestern (FAME)
Carburants et biocarburant - Assessment des méthodes determinations de la stabilité à
l'oxydation pour distillats et mélanges avec esters méthyliques d'acides gras (EMAG)
Ta slovenski standard je istoveten z: CEN/TR 17225:2018
ICS:
75.160.01 Goriva na splošno Fuels in general
SIST-TP CEN/TR 17225:2018 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TP CEN/TR 17225:2018
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SIST-TP CEN/TR 17225:2018
CEN/TR 17225
TECHNICAL REPORT
RAPPORT TECHNIQUE
September 2018
TECHNISCHER BERICHT
ICS 75.160.40; 75.160.20
English Version
Fuels and biofuels - Assessment on oxidation stability
determination methods for distillate fuels and blends
thereof with fatty acid methyl esters (FAME)
Carburants et biocarburant - Assessment des méthodes Mitteldestillatkraft- und -brennstoffe und
determinations de la stabilité à l'oxydation pour Biokraftstoffe - Bewertung der Verfahren zur
distillats et mélanges avec esters méthyliques d'acides Oxidationsstabilitätsbestimmung für
gras (EMAG) Mittteldestillatkraft- und -brennstoffe und deren
Mischungen mit Fettsäure-Methylestern (FAME)
This Technical Report was approved by CEN on 4 June 2018. It has been drawn up by the Technical Committee CEN/TC 19.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey 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
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 17225:2018 E
worldwide for CEN national Members.
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Contents Page
European foreword . 3
Introduction . 4
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 9
4 Test methods quantifying fuel ageing products . 10
4.1 History . 10
4.2 Generic oxidation stability test . 10
4.3 Turbine and mineral oil test . 11
4.4 Inherent storage stability. 12
4.5 Delta acid method and acid number determination after ageing at 115 °C . 12
4.6 High temperature stability . 13
5 Test methods determing the ageing reserve on the fuel . 13
5.1 General . 13
5.2 Rancimat. 13
5.3 Rancimat at 120 °C . 14
5.4 PetroOxy . 14
6 Differences in Rancimat and PetroOxy tests . 14
6.1 General . 14
6.2 Experimental studies on the share of fuel ageing at the Induction Period . 16
6.3 Discussion of pressure curve characteristics for the PetroOxy-Test (IPPetroOxy) . 17
6.4 Discussion of conductivity curve characteristics for the Rancimat test (IPRancimat). 18
7 Correlation between Rancimat (EN 15751) and PetroOxy (EN 16091) test methods . 21
8 Synopsis . 23
Annex A (informative) Share of fuel ageing on the Induction Period of the Rancimat- and
PetroOxy-tests . 25
Annex B (informative) Correlation exercise between PetroOxyand Rancimat . 29
Bibliography . 31
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European foreword
This document (CEN/TR 17225:2018) 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.
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.
During revisions of standards EN 14112, EN 15751, EN 16568 (Rancimat, [17]) and EN 16091
(PetroOxy), 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)” felt the need to create a document that provides extended
background information on oxidation stability test methods complementing the abstracts given in
Annex A of EN 14112, EN 15751 and EN 16568 as well as in Annex C of EN 16091.
This report also gives an overview about the work done by CEN/TC 19/JWG 1 on the correlation
between the Induction Period of the Rancimat and PetroOxy test methods.
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Introduction
All fuels, whether of fossil source or biogenic origin, constantly degrade. Although the bulk composition
remains widely unchanged, the presence of oxygen, higher temperature and catalytically active metals
accelerate oxidation of less stable compounds present, thus generating ageing products like acids
oligomers and polymeric compounds. The complex and varying composition of fossil diesel fuels and
the interactions of FAME and its inherent side-products with base diesel fuel components make it
difficult to understand fuel ageing mechanisms at a molecular level. The determination of oxidation
stability of fuels is therefore addressed by phenomenological techniques. Most test methods to
characterize fuel oxidation stability are based on the determination of specific parameters, e.g. polymer
formation, acidity increase, or oxygen consumption.
It has been established that the phenomenon of fuel ageing consists of two consecutive phases, starting
with the depletion of the ageing reserve with few chemical changes to the bulk material, followed by the
fuel ageing process itself during which the fuel is badly decomposed forming ageing polymers and acids
(Figure 1, Table 1). Fuel oxidation takes place via a free radical chain process, initiated by the
abstraction of a hydrogen atom from the fuel molecule and the addition of molecular oxygen to form
hydroperoxides.
Following chemical reactions proceed into two directions: a) Fragmentation of the molecule generates
aldehydes, ketones and short-chain carboxylic acids; b) interlinking of the molecules yielding oxygen
bridged dimers and polymers.
Diesel fuel oxidation is influenced by the chemical constituents of diesel fuel (e.g. specific sulphur- and
nitrogen-containing compounds) and contaminants (e.g. metal impurities). There are many different
chemical reactions, which can occur simultaneously and sequentially, fuel molecules are either
fragmented or increased in their size, e.g. by di-, oligo- and polymerization. These reactions rapidly
increase after a period when little or no chemical oxidation took place. This time interval before fuel
oxidation gets started significantly is called Induction Period.
Stress imposed on the fuel by heat in the presence of oxygen does not necessarily result in immediate
fragmentation or dimer/polymer formation. The reserve capacity of the fuel to resist oxidation is called
ageing reserve, which is related to the Induction Period [1, 2].
Test methods in Figure 1 marked with an asterisk are mentioned in this report for additional
information, but are not the focus of this work.
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Rancimat EN ISO 12205 [18], ASTM D2274 [19]
EN 14112 IP 306 mod.* [20]
EN 15751
EN 16568
PetroOxy ∆-acid no. method, JIS draft* [8],
CEN/TR 16885 [10], ASTM D6468* [22]
EN 16091
ASTM D7545 [21]
Key
1 period for the depletion of the ageing reserve (Induction Period)
2 ageing reserve
3 fuel ageing process, strong formation of acids and polymers
t time, h
Y property (such as acid number, conductivity, acidity, polymer formation, etc.)
Figure 1 — Two consecutive phases of fuel ageing and test methods relevant for each phase
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Table 1 — Overview about parameters and conditions of oxidation stability test methods
Rancimat PetroOxy IP 306 IP 306 mod. ∆-Acid
EN ISO 12205 ASTM D4625 ASTM D6468
method JIS
EN 14112 EN 16091
ASTM D2274
draft
EN 15751 ASTM D7545
EN 16568
Title
Determination Determination Determination Determination Modifications Standard test Determination Standard test
of oxidation of oxidation of the of oxidation proposed in method for of oxidation method for
stability by stability by oxidation stability of [3] to adapt distillate fuel stability of high
accelerated or rapid small stability of straight IP 306 to storage FAME-blended temperature
rapidly scale oxidation middle mineral oil diesel fuels, stability at diesel fuels stability of
accelerated test (RSSOT) distillate fuels FAME blends 43 °C distillate fuels
oxidation and neat
method FAME
Scope/Determina Oxidation Stability under Inherent Tendency of Inherent Inherent Acid value Relative
tion stability by accelerated stability of straight (i.e. stability under storage increase after stability of
means of oxidation middle plain) mineral accelerated stability of accelerated middle
measuring the conditions by distillate oil to oxidize, oxidation distillate fuels oxidation distillate fuels
Induction measuring the petroleum expressed as conditions under mild conditions under high
Period Induction fuels under total oxidation aging temperature
Period accelerated products conditions aging
oxidation (TOP) with limited conditions
conditions air exposure with limited
air exposure
(venting)
a
FAME content B100 B0 to B100 B0 B0 B0 to B100 [3] B0 B0 to B5 B0
(EN 14112) (EN ISO 12205
ASTM D2274)
B2 to B100 B0 to B7
(EN 15751)
B2 to B50
(EN 16568)
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Rancimat
PetroOxy IP 306 IP 306 mod. ∆-Acid
EN ISO 12205 ASTM D4625 ASTM D6468
method JIS
EN 14112 EN 16091
ASTM D2274
draft
EN 15751 ASTM D7545
EN 16568
Oxidation Ageing reserve Ageing reserve Fuel ageing Fuel ageing Fuel ageing Fuel ageing Fuel ageing Fuel ageing
stability + partial fuel behavior by behavior by behavior by behavior by behavior by behavior by
parameter ageing fuel oxidation fuel oxidation fuel oxidation fuel oxidation fuel oxidation fuel oxidation
products products products products products products
Parameter Induction Induction Amount of Amount of Amount of Amount of Acid increase light
Period by Period by total insoluble total insoluble total insoluble total insoluble by soluble reflectance by
conductivity oxygen sludge sludge + sludge + sludge acidity filterable
increase in pressure drop volatile acidity sludge from insoluble
water cell + soluble soluble sludge
acidity polymers +
volatile acidity
+ soluble
acidity
Sample amount 3,0 g 5 ml 350 ml 25 g 25 g 400 ml 350 ml 50 ml
(EN 14112)
7,5 g
(EN 15751)
7,5 g
(EN 16568)
Temperature 110 °C 140 °C 95 °C 120 °C 120 °C 43 °C 115 °C 150 °C
(EN 14112)
110 °C
(EN 15751)
120 °C
(EN 16568)
Time — — 16 h 48 h 16 h up to 24 16 h 1.5 or 3 h
weeks
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Rancimat
PetroOxy IP 306 IP 306 mod. ∆-Acid
EN ISO 12205 ASTM D4625 ASTM D6468
method JIS
EN 14112 EN 16091
ASTM D2274
draft
EN 15751 ASTM D7545
EN 16568
Oxidant 10 l/h Air 700 kPa 3 l/h Oxygen 1 l/h Oxygen 1 l/h Air ambient air 3 l/h Oxygen ambient air
Oxygen pressure, no
blow-through
Catalyst no no no no no no no no
Dilution of aged — — no no 10 to 20-fold no — —
fuel excess of
heptane for Bx
0,25
Precision 0,26 X + 0,23 0,086 3 X + 10,6 (0,1 X) precision for no full 2,20√X no precision -0,428 1 X +
b
(reproducibility) (EN 14112) 1,377 2 EN ISO 12205 insoluble validation available 44,08 (1,5 h)
(EN 16091) sludge not performed
0,1903 8 X + -0,303 4 X +
reported
0,3726 9 34,11 (3,0 h)
(EN 15751)
0,139 5 X +
0,288 8
(EN 16568)
Total insoluble sludge is defined as solid sediment (sum of filterable sludge and sludge adherent to the inner walls of the glass tube).
Sludge from soluble polymers is defined as the amount of polymers dissolved in the aged fuel but precipitated as sludge after dilution of the aged fuel with heptane.
Soluble acidity is defined as the acidity in the aged fuel sample.
Volatile acidity is defined as the acidity in the collecting vessel with the water phase.
a
FAME content which is validated with precision statement. Method can be applicable for blends containing higher FAME contents.
b
The precision of the test methods is given as complimentary information. Parameters and conditions of oxidation stability test methods are different limiting
the significance of a direct comparison of precision statements. x is the mean of two results.
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1 Scope
This document provides an overview of existing oxidation stability methods, with an emphasis on
differences between the Rancimat (EN 14112/EN 15751) and PetroOxy (EN 16091) tests.
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 14112, Fat and oil derivatives - Fatty Acid Methyl Esters (FAME) - Determination of oxidation stability
(accelerated oxidation test)
EN 15751, Automotive fuels - Fatty acid methyl ester (FAME) fuel and blends with diesel fuel -
Determination of oxidation stability by accelerated oxidation method
EN 16091, Liquid petroleum products - Middle distillates and fatty acid methyl ester (FAME) fuels and
blends - Determination of oxidation stability by rapid small scale oxidation method
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
ageing reserve
reserve capacity of the fuel to resist oxidation
3.2
break point
in the Rancimat test, the break point reflects the moment of beginning oxidation when the formation of
volatile acids increases rapidly; and in the PetroOxy test, the break point is the pressure which is 10 %
below the maximum pressure observed in the test apparatus
Note 1 to entry: The break point is differently defined depending on the testing procedure.
3.3
fuel ageing
oxidation of the fuel, forming ageing acids and polymers
3.4
Induction Period
IP
time elapsed until significant oxidation of fuel begins
3.5
inter-laboratory study
ILS
ring tests in which independent laboratories gather precision data for test methods using the same set
of subsamples
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3.6
sludge
insoluble, solid sediment formed during fuel oxidation
3.7
soluble acidity
amount of acidic hydrogen representing acids in the aged fuel sample
3.8
total acid number
quantity of potassium hydroxide used as a base to neutralize acids in fuels
3.9
total acidity
sum of soluble and volatile acidity
3.10
total insoluble sludge
sum of filterable sludge and sludge adherent to the inner walls of the test tube
3.11
volatile acidity
amount of acidic hydrogen representing acids in the collecting vessel with the water phase
4 Test methods quantifying fuel ageing products
4.1 History
Historically, the focus of laboratory tests for oxidation stability was on the second phase: quantifying
the products post ageing. In these tests, the fuel is treated with heat and air or pure oxygen for several
hours under well defined oxidation conditions. The polymeric and acidic fuel ageing products formed
are quantified. Ageing polymers, also commonly referred to as sludge, can be analysed following the
gravimetric procedures in EN ISO 12205 or ASTM D2274.
4.2 Generic oxidation stability test
In this type of test the amount of insolubles or sludge after ageing is determined. The test was
developed to estimate the storage stability of middle distillate fuels. Test conditions in EN ISO 12205
and ASTM D2274 are identical. The fuel is treated at 95 °C for 16 h while oxygen is bubbled through the
sample. Since specific field storage conditions differ from test conditions and also vary to some extent,
an accurate prediction of the amount of sludge that will form is not possible. Most diesel fuels and diesel
blends with FAME show only little sludge formation in this test because they are generally sufficiently
stable at 95 °C that their ageing reserve will not be completely depleted within 16 h [4]. Only extremely
unstable, e.g. thermally pre-stressed fuels, give significant sludge formation in the EN ISO 12205 test.
The lack of fuel differentiation by this method led to the development of tests under more severe
oxidation conditions, e.g. based on the IP 306 test that is performed at 120 °C. An additional reason to
not consider EN ISO 12205/ASTM D2274 as oxidation stability parameter of diesel/FAME blends was
the observation that only a part of the polymerized ageing products formed precipitates. A significant
amount of the polymerized ageing products remains in solution depending on the aromatic content of
diesel fuel, in particular if the aromatic content exceeds thirty volume percent [3].
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4.3 Turbine and mineral oil test
The procedure and test apparatus of IP 306 was originally developed for mineral turbine oil (IP 280
[5]). In the IP 306 test the total oxidation products are assessed: adherent and filterable sludge is
quantitatively determined by filtration. Soluble ageing acids in the aged fuel, and volatile ageing acids
driven by the stream of oxygen (IP 306) or air (modified IP 306) into the water phase of the collecting
vessel (Figure 2) are quantified by titration.
IP 306 was further modified. The temperature of 120 °C was maintained, but oxidation conditions were
further changed by replacing pure oxygen by air and by reducing the reaction time from 48 h to 16 h
[6]. Fossil diesel fuels in the standard range of oxidation stability have been found to be well
differentiated by IP 306 with these modifications.
With the introduction of FAME blended diesel fuels, however, it became apparent that test methods
evaluating oxidation stability by sludge formation produced unexpected results with higher FAME
content above B30 [3]. A part of the polymers formed during ageing does not precipitate and stays
dissolved in the aged fuel caused by the polarity increase associated with the increased share of FAME
in the blend. The portion of dissolved (and not measured) ageing polymers becomes bigger with
increasing FAME content. Thus for this type of test method, more polar diesel fuels with high FAME
blend rates produce less un-dissolved adherent and filterable sludge than neat mineral diesel fuel
suggesting a misleading conclusion that FAME diesel blends are more stable.
The total amount of solid sludge is a relevant parameter of the ageing state for a mineral diesel fuel.
Oxidation of diesel blends with higher shares of FAME, however, generates dissolved ageing polymers
to a significant extent. Soluble ageing polymers are known to be a major source for lacquering [7]. The
determination of all ageing polymers, independent of their solubility, is a relevant criterion for
oxidation stability of diesel blends with higher shares of FAME. Additionally, polymer solubility varies
because it is influenced by the changing nature of the aged fuel. Collection of all ageing polymers was
achieved when excess heptane was added after fuel ageing and prior to sludge filtration. Depending on
the FAME content in the blend, a 10- to 20-fold excess of heptane was used. Although results obtained
with these modifications were quite consistent, this test has not been further developed and validated
which impeded its publication as a new standard test method. Instead, further work concentrated on
the determination of the soluble acid concentration in aged fuel generated under similar conditions
(16 h at 115 °C).
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5
Key
1 fuel sample, aged fuel after test containing:
— insoluble (adherent and filterable) ageing polymers (sludge)
— soluble ageing polymers
— soluble ageing acids (soluble acidity)
2 distilled water in the collecting vessel, containing
— volatile ageing acids (volatile acidity)
3 oxidation tube
4 collecting vessel / absorption tube
5 stream of oxygen or air
Figure 2 — Type and location of fuel oxidation products as generated in the IP 306 test
4.4 Inherent storage stability
The focus of ASTM D4625 [23] is on the inherent storage stability of distillate fuels. After long storage
periods (4 weeks to 24 weeks) under mildly accelerated test conditions at 43 °C, the amount of total
insoluble sludge is determined. No air or oxygen is passed through the fuel. Oxygen needed for fuel
ageing is only supplied by ambient air. Compared to ASTM D2274 [19], fuel treatment according to
ASTM D4625 is closer to typical storage conditions and storage stability should be predicted more
reliably. The long testing periods, however, make this method unsuitable for quality control purposes.
4.5 Delta acid method and acid number determination after ageing at 115 °C
Substantial work on quantification of ageing acids evolving during fuel oxidation has been performed in
Japan [8]. In the delta acid method the fuel is aged at 115 °C for 16 h by passing a stream of oxygen
through the fuel using the oxidation cell employed in EN ISO 12205, and fuel acidity is measured by
titration. The acid number of the fuel before ageing is subtracted from the acid number of the aged fuel.
The acidity of the fuel before ageing is generally low and consists of few fuel acids only. Fatty acids can
be introduced by FAME blending, and some acidity may also be added from use of acidic lubricity
12
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additives. The acidity of the fuel after ageing is typically increased by ageing acids that form during
oxidation. Less volatile ageing acids are retained in the aged fuel, also frequently described as soluble
acids. Volatile acids generated in parallel during fuel oxidation are not captured nor accounted for.
Repeatability and reproducibility of the delta acid method as described in the Japanese draft has not
been considered to be sufficient. CEN/TC 19/JWG 1 decided to perform various round robin tests but no
substantial improvement of the precision could be reached, largely because the precision of both acid
titrations before and after ageing had to be regarded. It was concluded that this test set-up does not
allow improving precision to an acceptable level. The test results were summarized in a draft report,
presented to CEN/TC 19/JWG 1 in January 2011 and to CEN/TC 19/WG 24 in March 2014 [9].
In consequence, the approach of calculating a difference in the acid content before and after ageing was
abandoned. Soluble acid formation under the same oxidation conditions was addressed alone. A new
acid determination method after ageing was developed. However, issues with precision still have
persisted. The idea arose to develop a pass/fail criterion for the total amount of soluble acid after fuel
ageing using the General Discriminant Analysis tool, suggesting that fuels would develop either low or
high acid concentrations during oxidation. With this approach, however, a discrimination of fuels into
good and poor oxidation stability could not be achieved. After this effort was shown to be unsuccessful,
work on acid determination ceased. A summary of this work is published in CEN/TR 16885 [10].
4.6 High temperature stability
ASTM D6468 is a method that estimates the relative stability of middle distillate fuels by determining
the amount of sludge after filtration via reflection measurements. Ageing is performed at high
temperature (150 °C) for 90 min or 180 min and at limited air exposure. This method is applicable to
mineral diesel fuel but the method is less suitable for blends containing FAME because ageing polymers
from diesel and FAME are not coloured to the same extent, resulting in differing reflectance.
5 Test methods determing the ageing reserve on the fuel
5.1 General
The amount of fuel ageing products formed under defined ageing conditions does not necessarily
mirror the ageing reserve of the fuel. Before strong fuel ageing starts, the preceding step, the depletion
of the ageing reserve, can be assessed by several test methods. These methods measure the time period
before significant increase of ageing products occur when imposed with thermal load under defined
conditions.
5.2 Rancimat
The ageing reserve can be accurately monitored by means of accelerated oxidation tests EN 14112 and
EN 15751. Both tests are frequently referred to as ‘Rancimat’ and measure the Induction Period (IP), i.e.
how long the fuel is stable under standardized laboratory conditions at 110°C while fuel oxidation is
monitored by tracking volatile acids via conductivity increase. In these tests, the Induction Period is
defined as the time interval between the start of the measurement and the moment when the formation
of oxidation products begins to increase rapidly.
The conductivity is recorded in a measurement cell filled with water and equipped with a sensing
electrode. This cell is constantly flushed with the air passed through
...
SLOVENSKI STANDARD
kSIST-TP FprCEN/TR 17225:2018
01-april-2018
*RULYDLQELRJRULYD2FHQMHYDQMHPHWRGGRORþHYDQMDRNVLGDFLMVNHVWDELOQRVWL]D
GHVWLODWQDJRULYDLQQMLKRYHPHãDQLFH]PHWLOHVWULPDãþREQLKNLVOLQ )$0(
Fuels and biofuels - Assessment on oxidation stability determination methods for
distillate fuels and blends thereof with fatty acid methyl esters (FAME)
Mitteldestillatkraft- und -brennstoffe und Biokraftstoffe - Bewertung der Verfahren zur
Oxidationsstabilitätsbestimmung für Mittteldestillatkraft- und -brennstoffe und deren
Mischungen mit Fettsäure-Methylestern (FAME)
Carburants et biocarburant - Assessment des méthodes determinations de la stabilité à
l'oxydation pour distillats et mélanges avec esters méthyliques d'acides gras (EMAG)
Ta slovenski standard je istoveten z: FprCEN/TR 17225
ICS:
75.160.01 Goriva na splošno Fuels in general
kSIST-TP FprCEN/TR 17225:2018 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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kSIST-TP FprCEN/TR 17225:2018
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kSIST-TP FprCEN/TR 17225:2018
FINAL DRAFT
TECHNICAL REPORT
FprCEN/TR 17225
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
February 2018
ICS
English Version
Fuels and biofuels - Assessment on oxidation stability
determination methods for distillate fuels and blends
thereof with fatty acid methyl esters (FAME)
Carburants et biocarburant - Assessment des méthodes Mitteldestillatkraft- und -brennstoffe und
determinations de la stabilité à l'oxydation pour Biokraftstoffe - Bewertung der Verfahren zur
distillats et mélanges avec esters méthyliques d'acides Oxidationsstabilitätsbestimmung für
gras (EMAG) Mittteldestillatkraft- und -brennstoffe und deren
Mischungen mit Fettsäure-Methylestern (FAME)
This draft Technical Report is submitted to CEN members for Vote. It has been drawn up by the Technical Committee CEN/TC 19.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
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EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. FprCEN/TR 17225:2018 E
worldwide for CEN national Members.
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Contents Page
European foreword . 3
Introduction . 4
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 9
4 Test methods quantifying fuel ageing products . 10
4.1 History . 10
4.2 Generic oxidation stability test . 10
4.3 Turbine and mineral oil test . 11
4.4 Inherent storage stability. 12
4.5 Delta acid method and acid number determination after ageing at 115 °C . 12
4.6 High temperature stability . 13
5 Test methods determing the ageing reserve on the fuel . 13
5.1 General . 13
5.2 Rancimat. 13
5.3 Rancimat at 120 °C . 14
5.4 PetroOxy . 14
6 Differences in Rancimat and PetroOxy tests . 14
6.1 General . 14
6.2 Experimental studies on the share of fuel ageing at the Induction Period . 16
6.3 Discussion of pressure curve characteristics for the PetroOxy-Test (IPPetroOxy) . 17
6.4 Discussion of conductivity curve characteristics for the Rancimat test (IPRancimat). 18
7 Correlation between Rancimat (EN 15751) and PetroOxy (EN 16091) test methods . 21
8 Synopsis . 23
Annex A (informative) Share of fuel ageing on the Induction Period of the Rancimat- and
PetroOxy-tests . 25
Annex B (informative) Correlation exercise between PetroOxyand Rancimat . 29
Bibliography . 30
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European foreword
This document (FprCEN/TR 17225:2018) 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 document is currently submitted to the Vote on TR.
During revisions of standards EN 14112, EN 15751, EN 16568 (Rancimat, [17]) and EN 16091
(PetroOxy), 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)” felt the need to create a document that provides extended
background information on oxidation stability test methods complementing the abstracts given in
Annex A of EN 14112, EN 15751 and EN 16568 as well as in Annex C of EN 16091.
This report also gives an overview about the work done by CEN/TC 19/JWG 1 on the correlation
between the Induction Period of the Rancimat and PetroOxy test methods.
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Introduction
All fuels, whether of fossil source or biogenic origin, constantly degrade. Although the bulk composition
remains largely unchanged, the presence of oxygen, higher temperature and catalytically active metals
accelerate oxidation of less stable compounds present, thereby generating ageing acids and
oligomerization and polymerization products. The complex and varying composition of fossil diesel
fuels and the interactions of FAME and its inherent side-products with base diesel fuel components
make it difficult to understand fuel ageing mechanisms at a molecular level. The determination of
oxidation stability of fuels is therefore addressed by phenomenological techniques. Most test methods
to characterize fuel oxidation stability are based on the determination of specific parameters, e.g.
polymer formation, acidity increase, or oxygen consumption.
It has been established that the phenomenon of fuel ageing consists of two consecutive phases, starting
with the depletion of the ageing reserve with few chemical changes to the bulk material, followed by the
fuel ageing process itself during which the fuel is badly decomposed forming ageing polymers and acids
(Figure 1, Table 1). Fuel oxidation takes place via a free radical chain process, initiated by the
abstraction of a hydrogen atom from the fuel molecule and the addition of molecular oxygen to form
hydroperoxides.
Following chemical reactions proceed into two directions: a) Fragmentation of the molecule generates
aldehydes, ketones and short-chain carboxylic acids; b) interlinking of the molecules yielding oxygen
bridged dimers and polymers.
Diesel fuel oxidation is influenced by the chemical constituents of diesel fuel (e.g. specific sulphur- and
nitrogen-containing compounds) and contaminants (e.g. metal impurities). There are many different
chemical reactions, which can occur simultaneously and sequentially, fuel molecules are either
fragmented or increased in their size, e.g. by di-, oligo- and polymerization. These reactions rapidly
increase after a period when little or no chemical oxidation took place. This time interval before fuel
oxidation gets started significantly is called Induction Period.
Stress imposed on the fuel by heat in the presence of oxygen does not necessarily result in immediate
fragmentation or dimer/polymer formation. The reserve capacity of the fuel to resist oxidation is called
ageing reserve, which is related to the Induction Period [1, 2].
Test methods in Figure 1 marked with an asterisk are mentioned in this report for additional
information, but are not the focus of this work.
Rancimat EN ISO 12205 [18], ASTM D2274 [19]
EN 14112 IP 306 mod.* [20]
EN 15751
EN 16568
PetroOxy ∆-acid no. method, JIS draft* [8],
CEN/TR 16885 [10], ASTM D6468* [22]
EN 16091
ASTM D7545 [21]
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Key
1 period for the depletion of the ageing reserve (Induction Period)
2 ageing reserve
3 fuel ageing process, strong formation of acids and polymers
t time, h
Y property (such as acid number, conductivity, acidity, polymer formation, etc.)
Figure 1 — Two consecutive phases of fuel ageing and test methods relevant for each phase
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Table 1 — Overview about parameters and conditions of oxidation stability test methods
Rancimat PetroOxy IP 306 IP 306 mod. ∆-Acid
EN ISO 12205 ASTM D 4625 ASTM D 6468
method JIS
EN 14112 EN 16091
ASTM D 2274
draft
EN 15751 ASTM D 7545
EN 16568
Title
Determination Determination Determination Determination Modifications Standard test Determination Standard test
of oxidation of oxidation of the of oxidation proposed in method for of oxidation method for
stability by stability by oxidation stability of [3] to adapt sistillate fuel stability of high
accelerated or rapid small stability of straight IP 306 to storage FAME-blended temperature
rapidly scale oxidation middle mineral oil diesel fuels, stability at diesel fuels stability of
accelerated test (RSSOT) distillate fuels FAME blends 43 °C distillate fuels
oxidation and neat
method FAME
Scope/Determina Oxidation Stability under Inherent Tendency of Inherent Inherent Acid value Relative
tion stability by accelerated stability of straight (i.e. stability under storage increase after stability of
means of oxidation middle plain) mineral accelerated stability of accelerated middle
measuring the conditions by distillate oil to oxidize, oxidation distillate fuels oxidation distillate fuels
Induction measuring the petroleum expressed as conditions under mild conditions under high
Period Induction fuels under total oxidation aging temperature
Period accelerated products conditions aging
oxidation (TOP) with limited conditions
conditions air exposure with limited
air exposure
(venting)
a
FAME content B100 B0 to B100 B0 B0 B0 to B100 [3] B0 B0 to B5 B0
(EN 14112) (EN ISO 12205
ASTM D 2274)
B2 to B100 B0 to B7
(EN 15751)
B2 to B50
(EN 16568)
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Rancimat PetroOxy IP 306 IP 306 mod.
∆-Acid
EN ISO 12205 ASTM D 4625 ASTM D 6468
method JIS
EN 14112 EN 16091
ASTM D 2274
draft
EN 15751 ASTM D 7545
EN 16568
Oxidation Ageing reserve Ageing reserve Fuel ageing Fuel ageing Fuel ageing Fuel ageing Fuel ageing Fuel ageing
stability + partial fuel behavior by behavior by behavior by behavior by behavior by behavior by
parameter ageing fuel oxidation fuel oxidation fuel oxidation fuel oxidation fuel oxidation fuel oxidation
products products products products products products
Parameter Induction Induction Amount of Amount of Amount of Amount of Acid increase light
Period by Period by total insoluble total insoluble total insoluble total insoluble by soluble reflectance by
conductivity oxygen sludge sludge + sludge + sludge acidity filterable
increase in pressure drop volatile acidity sludge from insoluble
water cell + soluble soluble sludge
acidity polymers +
volatile acidity
+ soluble
acidity
Sample amount 3,0 g 5 ml 350 ml 25 g 25 g 400 ml 350 ml 50 ml
(EN 14112)
7,5 g
(EN 15751)
7,5 g
(EN 16568)
Temperature 110 °C 140 °C 95 °C 120 °C 120 °C 43 °C 115 °C 150 °C
(EN 14112)
110 °C
(EN 15751)
120 °C
(EN 16568)
Time — — 16 h 48 h 16 h up to 24 16 h 1.5 or 3 h
weeks
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Rancimat PetroOxy IP 306 IP 306 mod.
∆-Acid
EN ISO 12205 ASTM D 4625 ASTM D 6468
method JIS
EN 14112 EN 16091
ASTM D 2274
draft
EN 15751 ASTM D 7545
EN 16568
Oxidant 10 l/h Air 700 kPa 3 l/h Oxygen 1 l/h Oxygen 1 l/h Air ambient air 3 l/h Oxygen ambient air
Oxygen pressure, no
blow-through
Catalyst no no no no no no no no
Dilution of aged — — no no 10 to 20-fold no — —
fuel excess of
heptane for Bx
0,25
Precision 0,26 X + 0,23 0,086 3 X + 10,6 (0,1 X) precision for no full 2,20√X no precision -0,428 1 X +
b
(reproducibility) (EN 14112) 1,377 2 EN ISO 12205 insoluble validation available 44,08 (1,5 h)
(EN 16091) sludge not performed
0,1903 8 X + -0,303 4 X +
reported
0,3726 9 34,11 (3,0 h)
(EN 15751)
0,139 5 X +
0,288 8
(EN 16568)
Total insoluble sludge is defined as solid sediment (sum of filterable sludge and sludge adherent to the inner walls of the glass tube).
Sludge from soluble polymers is defined as the amount of polymers dissolved in the aged fuel but precipitated as sludge after dilution of the aged fuel with heptane.
Soluble acidity is defined as the acidity in the aged fuel sample.
Volatile acidity is defined as the acidity in the collecting vessel with the water phase.
a
FAME content which is validated with precision statement. Method can be applicable for blends containing higher FAME contents.
b
The precision of the test methods is given as complimentary information. Parameters and conditions of oxidation stability test methods are different limiting
the significance of a direct comparison of precision statements. x is the mean of two results.
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1 Scope
This document provides an overview of existing oxidation stability methods, with an emphasis on
differences between the Rancimat (EN 14112/EN 15751) and PetroOxy (EN 16091) tests.
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 14112, Fat and oil derivatives - Fatty Acid Methyl Esters (FAME) - Determination of oxidation stability
(accelerated oxidation test)
EN 15751, Automotive fuels - Fatty acid methyl ester (FAME) fuel and blends with diesel fuel -
Determination of oxidation stability by accelerated oxidation method
EN 16091, Liquid petroleum products - Middle distillates and fatty acid methyl ester (FAME) fuels and
blends - Determination of oxidation stability by rapid small scale oxidation method
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
ageing reserve
reserve capacity of the fuel to resist oxidation
3.2
break point
in the Rancimat test, the break point reflects the moment of beginning oxidation when the formation of
volatile acids increases rapidly; and in the PetroOxy test, the break point is the pressure which is 10 %
below the maximum pressure observed in the test apparatus
Note 1 to entry: The break point is differently defined depending on the testing procedure.
3.3
fuel ageing
oxidation of the fuel, forming ageing acids and polymers
3.4
Induction Period
IP
time elapsed until significant oxidation of fuel begins
3.5
inter-laboratory study
ILS
ring tests in which independent laboratories gather precision data for test methods using the same set
of subsamples
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3.6
sludge
insoluble, solid sediment formed during fuel oxidation
3.7
soluble acidity
amount of acidic hydrogen representing acids in the aged fuel sample
3.8
total acid number
quantity of potassium hydroxide used as a base to neutralize acids in fuels
3.9
total acidity
sum of soluble and volatile acidity
3.10
total insoluble sludge
sum of filterable sludge and sludge adherent to the inner walls of the test tube
3.11
volatile acidity
amount of acidic hydrogen representing acids in the collecting vessel with the water phase
4 Test methods quantifying fuel ageing products
4.1 History
Historically, the focus of laboratory tests for oxidation stability was on the second phase: quantifying
the products post ageing. In these tests, the fuel is treated with heat and air or pure oxygen for several
hours under well defined oxidation conditions. The polymeric and acidic fuel ageing products formed
are quantified. Ageing polymers, also commonly referred to as sludge, can be analysed following the
gravimetric procedures in EN ISO 12205 or ASTM D2274.
4.2 Generic oxidation stability test
In this type of test the amount of insolubles or sludge after ageing is determined. The test was
developed to estimate the storage stability of middle distillate fuels. Test conditions in EN ISO 12205
and ASTM D2274 are identical. The fuel is treated at 95 °C for 16 h while oxygen is bubbled through the
sample. Since specific field storage conditions differ from test conditions and also vary to some extent,
an accurate prediction of the amount of sludge that will form is not possible. Most diesel fuels and diesel
blends with FAME show only little sludge formation in this test because they are generally sufficiently
stable at 95 °C that their ageing reserve will not be completely depleted within 16 h [4]. Only extremely
unstable, e.g. thermally pre-stressed fuels, give significant sludge formation in the EN ISO 12205 test.
The lack of fuel differentiation by this method led to the development of tests under more severe
oxidation conditions, e.g. based on the IP 306 test that is performed at 120 °C. An additional reason to
not consider EN ISO 12205/ASTM D2274 as oxidation stability parameter of diesel/FAME blends was
the observation that only a part of the polymerized ageing products formed precipitates. A significant
amount of the polymerized ageing products remains in solution depending on the aromatic content of
diesel fuel, in particular if the aromatic content exceeds thirty volume percent [3].
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4.3 Turbine and mineral oil test
The procedure and test apparatus of IP 306 was originally developed for mineral turbine oil (IP 280
[5]). In the IP 306 test the total oxidation products are assessed: adherent and filterable sludge is
quantitatively determined by filtration. Soluble ageing acids in the aged fuel, and volatile ageing acids
driven by the stream of oxygen (IP 306) or air (modified IP 306) into the water phase of the collecting
vessel (Figure 2) are quantified by titration.
IP 306 was further modified. The temperature of 120 °C was maintained, but oxidation conditions were
further changed by replacing pure oxygen by air and by reducing the reaction time from 48 h to 16 h
[6]. Fossil diesel fuels in the standard range of oxidation stability have been found to be well
differentiated by IP 306 with these modifications.
With the introduction of FAME blended diesel fuels, however, it became apparent that test methods
evaluating oxidation stability by sludge formation produced unexpected results with higher FAME
content above B30 [3]. A part of the polymers formed during ageing does not precipitate and stays
dissolved in the aged fuel caused by the polarity increase associated with the increased share of FAME
in the blend. The portion of dissolved (and not measured) ageing polymers becomes bigger with
increasing FAME content. Thus for this type of test method, more polar diesel fuels with high FAME
blend rates produce less un-dissolved adherent and filterable sludge than neat mineral diesel fuel
suggesting a misleading conclusion that FAME diesel blends are more stable.
The total amount of solid sludge is a relevant parameter of the ageing state for a mineral diesel fuel.
Oxidation of diesel blends with higher shares of FAME, however, generates dissolved ageing polymers
to a significant extent. Soluble ageing polymers are known to be a major source for lacquering [7]. The
determination of all ageing polymers, independent of their solubility, is a relevant criterion for
oxidation stability of diesel blends with higher shares of FAME. Additionally, polymer solubility varies
because it is influenced by the changing nature of the aged fuel. Collection of all ageing polymers was
achieved when excess heptane was added after fuel ageing and prior to sludge filtration. Depending on
the FAME content in the blend, a 10- to 20-fold excess of heptane was used. Although results obtained
with these modifications were quite consistent, this test has not been further developed and validated
which impeded its publication as a new standard test method. Instead, further work concentrated on
the determination of the soluble acid concentration in aged fuel generated under similar conditions
(16 h at 115 °C).
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5
Key
1 fuel sample, aged fuel after test containing:
— insoluble (adherent and filterable) ageing polymers (sludge)
— soluble ageing polymers
— soluble ageing acids (soluble acidity)
2 distilled water in the collecting vessel, containing
— volatile ageing acids (volatile acidity)
3 oxidation tube
4 collecting vessel / absorption tube
5 stream of oxygen or air
Figure 2 — Type and location of fuel oxidation products as generated in the IP 306 test
4.4 Inherent storage stability
The focus of ASTM D4625 [23] is on the inherent storage stability of distillate fuels. After long storage
periods (4 weeks to 24 weeks) under mildly accelerated test conditions at 43 °C, the amount of total
insoluble sludge is determined. No air or oxygen is passed through the fuel. Oxygen needed for fuel
ageing is only supplied by ambient air. Compared to ASTM D2274 [19], fuel treatment according to
ASTM D4625 is closer to typical storage conditions and storage stability should be predicted more
reliably. The long testing periods, however, make this method unsuitable for quality control purposes.
4.5 Delta acid method and acid number determination after ageing at 115 °C
Substantial work on quantification of ageing acids evolving during fuel oxidation has been performed in
Japan [8]. In the delta acid method the fuel is aged at 115 °C for 16 h by passing a stream of oxygen
through the fuel using the oxidation cell employed in EN ISO 12205, and fuel acidity is measured by
titration. The acid number of the fuel before ageing is subtracted from the acid number of the aged fuel.
The acidity of the fuel before ageing is generally low and consists of few fuel acids only. Fatty acids can
be introduced by FAME blending, and some acidity may also be added from use of acidic lubricity
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additives. The acidity of the fuel after ageing is typically increased by ageing acids that form during
oxidation. Less volatile ageing acids are retained in the aged fuel, also frequently described as soluble
acids. Volatile acids generated in parallel during fuel oxidation are not captured nor accounted for.
Repeatability and reproducibility of the delta acid method as described in the Japanese draft has not
been considered to be sufficient. CEN/TC 19/JWG 1 decided to perform various round robin tests but no
substantial improvement of the precision could be reached, largely because the precision of both acid
titrations before and after ageing had to be regarded. It was concluded that this test set-up does not
allow improving precision to an acceptable level. The test results were summarized in a draft report,
presented to CEN/TC 19/JWG 1 in January 2011 and to CEN/TC 19/WG 24 in March 2014 [9].
In consequence, the approach of calculating a difference in the acid content before and after ageing was
abandoned. Soluble acid formation under the same oxidation conditions was addressed alone. A new
acid determination method after ageing was developed. However, issues with precision still have
persisted. The idea arose to develop a pass/fail criterion for the total amount of soluble acid after fuel
ageing using the General Discriminant Analysis tool, suggesting that fuels would develop either low or
high acid concentrations during oxidation. With this approach, however, a discrimination of fuels into
good and poor oxidation stability could not be achieved. After this effort was shown to be unsuccessful,
work on acid determination ceased. A summary of this work is published in CEN/TR 16885 [10].
4.6 High temperature stability
ASTM D6468 is a method that estimates the relative stability of middle distillate fuels by determining
the amount of sludge after filtration via reflection measurements. Ageing is performed at high
temperature (150 °C) for 90 min or 180 min and at limited air exposure. This method is applicable to
mineral diesel fuel but the method is less suitable for blends containing FAME because ageing polymers
from diesel and FAME are not coloured to the same extent, resulting in differing reflectance.
5 Test methods determing the ageing reserve on the fuel
5.1 General
The amount of fuel ageing products formed under defined ageing conditions does not necessarily
mirror the ageing reserve of the fuel. Before strong fuel ageing starts, the preceding step, the depletion
of the ageing reserve, can be assessed by several test methods. These methods measure the time period
before significant increase of ageing products occur when imposed with thermal load under defined
conditions.
5.2 Rancimat
The ageing reserve can be accurately monitored by means of accelerated oxidation tests EN 14112 and
EN 15751. Both tests are frequently referred to as ‘Rancimat’ and measure the Induction Period (IP), i.e.
how long the fuel is stable under standardized laboratory conditions at 110°C while fuel oxidation is
monitored by tracking volatile acids via conductivity increase. In these tests, the Induction Period is
defined
...
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