EN ISO 17507-1:2025

SLOVENSKI STANDARD
oSIST prEN ISO 17507-1:2024
01-december-2024
[Not translated]
Natural gas - Calculation of methane number of gaseous fuels for reciprocating internal
combustion engines - Part 1: MNc method (ISO/DIS 17507-1:2024)
Erdgas-Berechnung der Methanzahl von gasförmigen Kraftstoffen für
Verbrennungsmotoren-Teil 1: MNc-Verfahren (ISO/DIS 17507-1:2024)
Gaz naturel - Calcul de l'indice de méthane des combustibles gazeux pour les moteurs
alternatifs à combustion interne - Partie 1: Méthode IMc (ISO/DIS 17507-1:2024)
Ta slovenski standard je istoveten z: prEN ISO 17507-1
ICS:
75.060 Zemeljski plin Natural gas
oSIST prEN ISO 17507-1:2024 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN ISO 17507-1:2024
oSIST prEN ISO 17507-1:2024
DRAFT
International
Standard
ISO/DIS 17507-1
ISO/TC 193
Natural gas — Calculation of
Secretariat: NEN
methane number of gaseous
Voting begins on:
fuels for reciprocating internal
2024-10-17
combustion engines —
Voting terminates on:
2025-01-09
Part 1:
MNc method
ICS: 75.060
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
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Reference number
ISO/DIS 17507-1:2024(en)
oSIST prEN ISO 17507-1:2024
DRAFT
ISO/DIS 17507-1:2024(en)
International
Standard
ISO/DIS 17507-1
ISO/TC 193
Natural gas — Calculation of
Secretariat: NEN
methane number of gaseous
Voting begins on:
fuels for reciprocating internal
combustion engines —
Voting terminates on:
Part 1:
MNc method
ICS: 75.060
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2024
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
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Published in Switzerland Reference number
ISO/DIS 17507-1:2024(en)
ii
oSIST prEN ISO 17507-1:2024
ISO/DIS 17507-1:2024(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 2
5 MNc method . . 2
5.1 Introduction .2
5.2 Applicability .2
5.2.1 Standard gaseous fuel composition range .2
5.2.2 Handling of other gaseous fuel components .3
5.3 Methodology to calculate the MNc .3
5.4 Expression of results . .4
5.5 Uncertainty error and bias .4
6 Example calculations . 4
6.1 Example 1 .4
6.1.1 Simplification of the composition of the gaseous fuel . .4
6.1.2 Selection of the ternary systems .5
6.1.3 Sub-division of the inert-free mixture into the selected partial mixtures .8
6.1.4 Calculation of the methane number of the partial mixtures .8
6.1.5 Criteria for not using ternary systems for final calculation of the MNc .8
6.1.6 Adjustment of the composition and fraction of the partial mixtures .8
6.1.7 Calculation of the methane number of the simplified mixture.9
6.1.8 Calculation of the methane number of the gaseous fuel .10
6.2 Example 2 .10
6.2.1 Simplification of the composition of the gaseous fuel . .10
6.2.2 Calculation of fitness of the ternary systems .10
6.2.3 Selection of ternary mixtures.10
6.2.4 Calculation of the methane number .11
6.3 Example 3 .11
6.3.1 Simplification of the composition of the gaseous fuel . .11
6.3.2 Calculation of fitness of the ternary systems .11
6.3.3 Selection of ternary mixtures.11
6.3.4 Calculation of the methane number . 12
6.3.5 Additional numerical examples . 12
Annex A (normative) Numerical results of calculations for a variety of compositions for
software validation purposes .13
Annex B (informative) Tools for users of the MNc Method .27
Annex C (normative) Uncertainty error and bias .28
Annex D (informative) Natural gas-based fuels for reciprocating internal combustion engines .30
Annex E (informative) Basis of the MNc Method .31
Bibliography .36

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oSIST prEN ISO 17507-1:2024
ISO/DIS 17507-1:2024(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
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related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 193, Natural gas.
A list of all parts in the ISO 17507 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

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Introduction
The globalization of the natural gas market and the drive towards sustainability are increasing the diversity
of the supply of gases to the natural gas infrastructure. For example, the introduction of regasified LNG
can result in higher fractions of non-methane hydrocarbons in the natural gas grid than the traditionally
distributed pipeline gases for which these hydrocarbons have been removed during processing. Also, the
drive towards the introduction of sustainable gaseous fuels such as hydrogen and gases derived from
biomass results in the introduction of “new” gas compositions, containing components that do not occur
in the traditional natural gas supply. Consequently, the increasing variations in gas composition affect
the so-called knock resistance of the gas when used as a fuel which can affect the operational integrity of
reciprocating internal combustion engines.
For the efficient and safe operation of gas engines, it is of great importance to characterize the knock
resistance of gaseous fuels accurately. Engine knock is caused by autoignition of unburned fuel mixture ahead
of this mixture being consumed by the propagating flame. Mild engine knock increases pollutant emissions
accompanied by gradual build-up of component damage and complete engine failure if not counteracted.
Severe knock causes structural damage to critical engine parts, quickly leading to catastrophic engine
failure. To ensure that gas engines are matched with the expected variations in fuel composition, the knock
resistance of the fuel is to be characterized, and subsequently specified, unambiguously.
Traditional methods for characterizing the knock resistance of gaseous fuels, such as the methane number
method developed by AVL in the 1960s, relate the knock propensity of a given fuel with that of an equivalent
methane/hydrogen mixture using a standardized test engine. Several other methane number methods have
since been developed, sometimes based on the approach and/or data from the original experimental work
performed by AVL.
In recognition of the need for standardizing a method for characterizing the knock resistance of gaseous
fuels, several existing methods for calculating a methane number have been considered including the MNc
[1]
method which is described in this document. ISO 17507-2 describes the PKI method.
Methods to calculate a methane number are based on the input of the gas composition under investigation.
While methods may be fundamentally different in their development approach, the methods should produce
ideally similar methane numbers for the range of gas compositions they are valid for. Yet, differences in
outcome can be observed. Engine manufacturers typically determine the calculation method to be used
when specifying a methane number value for their engines as part of their application and warranty
statements. In all cases, when specifying a methane number based on either method, or any other method,
the method used should be noted.
The MNc method is based on the original data of the research program performed by AVL Deutschland
[2]
(AVL is based in Graz, Austria) GmbH for FVV (the Research Association for Combustion Engines). The
[3] [4]
methodology first proposed by Deutz (“Klöckner-Humboldt-Deutz AG”) , was later amended in 2005 and
2011 by MWM (“Motoren-Werke Mannheim AG”). A more detailed history of the MNc method can be found
in Annex E.
The MNc method takes the components of the gaseous fuel mixture and groups them together into several
ternary and binary groups whose methane number has been experimentally determined. It then determines
the overall methane number by applying optimization algorithms to the individual component groupings.

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oSIST prEN ISO 17507-1:2024
DRAFT International Standard ISO/DIS 17507-1:2024(en)
Natural gas — Calculation of methane number of gaseous
fuels for reciprocating internal combustion engines —
Part 1:
MNc method
1 Scope
The methane number of a gas quantifies the knock propensity of that gas when used as a fuel in a
reciprocating internal combustion engine. The higher the methane number, the more knock resistant the
gaseous fuel is, and vice versa.
This document defines the MNc method for the calculation of the methane number of a gaseous fuel, using
the composition of the gas as sole input for the calculation.
This document applies to natural gas (and biomethane) and their admixtures with hydrogen, see Clause 5.
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.
ISO 14532:2014, Natural gas — Vocabulary
ISO 14912, Gas analysis — Conversion of gas mixture composition data
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14532 and the following 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
methane number
MN
numerical rating indicating the knock resistance of a gaseous fuel
Note 1 to entry: It is analogous to the octane number for petrol. The methane number is the volume fraction expressed
as percentage of methane in a methane-hydrogen mixture, that in a test engine under standard conditions has the
same knock resistance as the fuel gaseous fuel to be examined.
[SOURCE: ISO 14532:2014, 2.6.6.1]

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3.2
Calculated methane number
MNc
calculation of a numerical rating index indicating the knock resistance of a gaseous fuel according to
ISO 17507-1
Note 1 to entry: This analytical estimate of a methane number is based on using volume fraction gaseous fuel
composition as input.
4 Symbols and abbreviated terms
— MN Methane Number
— MNc Calculated Methane Number
5 MNc method
5.1 Introduction
The methane number of a gaseous fuel is calculated from its composition according to several different
methods, all of which can give different results. The MNc method (the so-called “MWM Method”) is in use
by engine Original Equipment Manufacturers (OEMs), gaseous fuel suppliers, engine operators, consulting
[5]
engineers and engine control gas analyser equipment OEMs and has been adopted in EN 16726 and as the
[6]
ASTM D8221. When referring to a methane number value, the method used should be noted.
[7]
NOTE The MNc method is cited as a test method in ISO 23306 .
The MNc method described in this document has been developed for a range of gas compositions exceeding
the typical composition range of natural gas-based fuels used in reciprocating internal combustion engines
shown in Table D.1.
The MNc method thus can be used for the calculation of the methane number of any gaseous fuel as long
as the gas composition input ranges, shown in Table 1, and further boundary conditions of this method are
adhered to. The boundary conditions for the MNc method are set out in this document.
The method is based on gaseous fuel compositions in volume fraction at reference conditions of 0 °C and
101,325 kPa and expressed as a percentage. If the gas composition is available either as mole fraction or as
[8]
mass fraction, conversion to volume fraction shall be performed using the methods in ISO 14912 .
Numerical examples are provided to enable software developers to validate implementations of the
methodology described in this document. As an aid to validation a relatively large number of decimal places
has been retained.
5.2 Applicability
5.2.1 Standard gaseous fuel composition range
The MNc method described in this document has been developed for and is applicable to all reciprocating
internal combustion engines using a gaseous fuel.
In general, the use of any method for calculating the methane number of a gaseous fuel requires careful
consideration and/or consultation with specialist industry parties such as engine suppliers, fuel suppliers
and consulting firms.
The method described in this document is applicable to gaseous fuels comprising the following gases:
carbon monoxide; butadiene; butylene; ethylene; propylene; hydrogen sulfide; hydrogen; propane; ethane;
butane; methane; nitrogen and carbon dioxide. The method treats hydrocarbons other than those specified
as butane and is therefore applicable to gaseous fuels containing such higher hydrocarbons.

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Upper limits for gaseous fuels applied to this method are shown in Table 1. Lower limits are zero for all
components.
Table 1 — Upper limits of gaseous fuel components for the MNc method
Amount of substance
b b
Volume fraction Mole fraction Mass fraction
Component
% % %
(normative) (informative) (informative)
Methane 100 100 100
Ethylene 100 100 100
Ethane 100 100 100
Propylene 100 100 100
Propane 100 100 100
Butanes 100 100 100
a
Pentanes 3 3,23 13,04
a
Hexanes+ 3 3,34 15,66
Nitrogen 100 100 100
Carbon dioxide 60 60,11 80,52
Carbon monoxide 100 100 100
Hydrogen 100 100 100
Hydrogen sulfide 25 25,15 41,65
a
The MNc method for compositions including pentanes (C5), and hexanes and higher (C6+) is limited to C5 and C6+ volume
fraction of 3 % each and a total of 5 %.
b
Limits expressed as mole fractions and mass fractions, other than 100 %, are converted from the limits in volume fraction
according to ISO 14912. Because the conversion is composition-dependant, the calculation assumes the component is present
as a binary mixture with methane. Limits expressed as mole fractions and mass fractions, other than 100 %, are therefore
informative.
5.2.2 Handling of other gaseous fuel components
5.2.2.1 Oxygen and water vapour
Oxygen and water vapour shall be ignored, and the gaseous fuel composition shall be normalized as an
oxygen-free composition.
5.2.2.2 Argon and helium
Any volume fractions of argon or helium present in the gaseous fuel under investigation shall be assigned to
the fraction of nitrogen.
5.2.2.3 Other non-listed gaseous fuel components
Any component present in the gaseous fuel under investigation not listed as valid gas input component for
the MNc method as per Table 1 and not listed in 5.2.2.1 or 5.2.2.2, shall be ignored, and the gaseous fuel
composition shall be normalized without that component.
5.3 Methodology to calculate the MNc
The methane number of a gaseous fuel is calculated from its composition in five steps. The steps are outlined
below and described more fully in turn in an example composition in 6.1. Additional examples are discussed

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in 6.2 and 6.3 and Annex A contains the numerical values and results of those calculations. Table A.10
provides results of calculations for more example compositions for further software validation purposes.
a) The composition of the gaseous fuel is simplified by converting it into an inert-free mixture comprising
the combustible compounds carbon monoxide, ethylene, propylene, hydrogen sulfide, hydrogen,
propane, ethane, butane and methane.
For gases conveyed in pipeline systems carbon monoxide, ethylene, propylene, hydrogen sulfide is unlikely
to be present at concentrations that would impact on methane number and can be ignored.
b) The simplified mixture is sub-divided further into a number of partial ternary mixtures. The number
and particular partial ternary mixtures chosen is decided by inspection of available ternary systems in
a given order, including those systems that contain the relevant combustible compounds. Selection is
ceased when all combustible compounds are contained in at least two ternary systems.
c) The composition and fraction of the selected partial mixtures is adjusted iteratively so as to minimize
the difference between the methane numbers of each partial mixture.
d) The methane number of the simplified mixture is determined from the weighted average of the methane
number of the selected partial mixtures.
e) Finally, the methane number of the gaseous fuel is calculated by correcting the methane number of the
simplified mixture to allow for the presence of inerts in the original gaseous fuel.
5.4 Expression of results
For expression of the final result, the calculated methane number, is expressed as an integer and the method
[9]
used should be noted. E.g., 74 MNc per ISO 17507-1. Rounding to an integer value according to ISO 80000-1
is recommended as a higher numerical resolution of the MNc value is not relevant in practice.
5.5 Uncertainty error and bias
The MNc is calculated from the volume fraction composition of the gaseous fuel under review as sole input.
The calculation uses fixed-value coefficients based on the particular composition of the gaseous fuel under
review, meaning that for a given gaseous fuel composition there can only be one MNc value. For the purpose
of this standard, the MNc values thus calculated are deemed to be exact according to the MNc method. Hence,
any error or bias in an MNc value arise solely from errors in the gaseous fuel compositions used as input.
The resulting uncertainty shall be estimated according to Annex C.
6 Example calculations
6.1 Example 1
6.1.1 Simplification of the composition of the gaseous fuel
The description of the calculation is illustrated by reference to a gaseous fuel composition typical of natural
gas as shown in Table A.1. The composition of the gas (column 1) is simplified by increasing the quantity
of butanes to allow for the presence of butadiene, butylene, pentanes and hydrocarbons of carbon number
greater than 5. The adjustment made is as follows:
— Butadiene and butylene are replaced with an equivalent number of butanes by multiplying their
quantities by 1.
— Pentanes are replaced with an equivalent number of butanes by multiplying the quantity of pentanes by 2,3.
— Hydrocarbons of carbon number greater than 5 (“hexanes+”) are replaced with an equivalent number of
butanes by multiplying the quantity of hexanes+ by 5,3.
In the case of example 1 the quantity of butanes

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= 0,210 0 + 0,190 0 + (0,040 0 + 0,050 0) · 2,3 + 0,060 0 · 5,3
= 0,925 0 (Column 2)
The simplified mixture is then re-normalized to 100 % (Column 3).
6.1.2 Selection of the ternary systems
6.1.2.1 Ternary mixtures
The ternary mixtures are chosen from the following list:
— A1: Methane – Hydrogen – Ethane
— A2: Propane – Ethane – Butane
— A3: Hydrogen – Propane – Propylene
— A4: Methane – Ethane – Propane
— A5: Methane – Hydrogen – Propane
— A6: Methane – Hydrogen – Butane
— A7: Methane – Propane – Butane
— A8: Methane – Ethane – Butane
— A9: Methane – Ethylene – Butane
— A10: Methane – Hydrogen sulfide – Butane
— A11: Methane – Ethane – Hydrogen sulfide
— A12: Methane – Propylene
— A13: Ethane – Propylene
— A14: Carbon monoxide – Hydrogen
— A15: Ethane – Ethylene
— A16: Propane – Ethylene
NOTE Mixtures A12 – A16 are clearly not ternary systems; however, for ease of mathematical treatment the
coefficients have been adjusted so as to allow the expression of the methane number using a single equation.
6.1.2.2 Range of applicability of ternary mixture data
The range of applicability of most ternary systems is wide and Table A.2 provides the range of applicability
values which are expressed as maximum and minimum content of each component. However, for some
ternary systems there is a reduced range of applicability which is of major importance when selecting
ternary mixtures.
Table 2 shows the how the additional tolerance of 15,0 % for x(min), y(max), z(max) for the four ternary
systems (A9, A10, A11, and A20) is to be applied.

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Table 2 — Tolerances for x(min), y(max) and z(max) for A9, A10, A11 and A20
A9 A10 A11 A20
x: methane methane methane methane
y: ethylene hydrogen sulfide ethane carbon dioxide
z: butane butane hydrogen sulfide nitrogen
x(max), volume fraction / % 100,0 100,0 100,0 100,0
x(min), volume fraction / % 60,0 (75,0-15) 40,0(25,0+15) 40,0(25,0+15) 25,0(40,0-15)
y(max), volume fraction / % 40,0(25,0+15) 40,0(25,0+15) 40,0(25,0+15) 75,0(60,0+15)
y(min), volume fraction / % 0,0 0,0 0,0 0,0
z(max), volume fraction / % 40,0(25,0+15) 40,0(25,0+15) 40,0(25,0+15) 75,0(60,0+15)
z(min), volume fraction / % 0,0 0,0 0,0 0,0
Table A.3 describes the tolerances used for calculating the fitness for 𝑉sum, but these boundary conditions
are also valid during the optimization by varying the quantity of each gas component of the partial ternary
system for the final calculation of the MN.
6.1.2.3 Factors affecting the ternary system selection process
The ternary systems are selected in accordance with three main considerations:
a) The number of gases in the ternary system that are present in the simplified mixture. Priority is always
given to ternary systems that have all three of their components present in the simplified mixture.
Systems with two of their components present in the simplified mixture are acceptable if insufficient
systems with three components present in the simplified mixture are available.
b) Where there is a choice of ternary systems, the system with the highest fitness, Wj, takes priority.
c) Each component in the simplified mixture shall be represented in at least two ternary systems.
Fitness of a system is calculated from the following Formula:
Vm·,in 100 Vmax +15
()()
in=
ii,j
W = (1)
j
∑
i=1
Vsum
i
where
n is the number of components in the simplified mixture;
V is the volume fraction of component i in the simplified mixture;
i
Vmax is the maximum content of component i for the range of applicability of system j;
i, j
Vsum is the sum of all maximum contents of component i for the range of applicability of all systems?
i
i.e.,
j=18
Vsum =+minV100, max 15 (2)
()()
ii,j
∑
i=1
Values of Vsumi are independent of the composition of the simplified mixture. However, Wj is dependent
upon the composition of the simplified mixture and so shall be calculated prior to selection.
NOTE This also means that the choice of ternary mixtures can be different for mixtures containing the same
components, but in different proportions.
In the case of example 1, the calculation of Vsumi and Wj is shown in Tables A.3 and A.4.

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6.1.2.4 Description of the ternary system selection process
The aim is to identify the optimum number of ternary systems that meet the three criteria described in
5.3.2.3 and this is achieved by consideration of each component present in the simplified mixture in the
following sequence:
1) Carbon monoxide
2) Butadiene
3) Butylene
4) Ethylene
5) Propylene
6) Hydrogen sulfide
7) Hydrogen
8) Propane
9) Ethane
10) Butane
11) Methane
Step 1: For the first component in the simplified mixture, one ternary system that contains that component
is selected. The priority of selection is as follows:
a) Ternary systems with all three components present in the simplified mixture have priority over systems
having one or two components present.
b) The ternary mixture with the highest fitness has priority.
Step 2: Consideration is then given to the second component in the simplified mixture. If this component is
not present in the ternary system selected for the first component, then a ternary system is selected for this
component using the same priority of selection as in step 1. If, however, the ternary system selected for the
first component contains the second component, then the selection proceeds for the third component (step 3).
Step 3: Consideration is then given to third, fourth, fifth, etc. components in the same manner as Steps 1-2.
Step 4: When all components in the simplified mixture have been examined once, steps 1-3 are repeated in
the same component order. If any component is represented in only one selected ternary mixture, then an
additional ternary mixture is selected, again using the same priority of selection as in step 1.
The selection process ends when all components in the simplified mixture are represented in at least two
ternary systems.
In the case of example 1:
— The first component in the simplified mixture is propane and this is present in four ternary systems that have
all their components present in the simplified mixture – A2, A4, A7 and A8. In this case, A4 is selected because
it has the largest value of fitness (i.e., 10,313 8).
— The second component in the simplified mixture is ethane and this is already represented in system A4, so no
ternary mixture is selected.
— The third component of the simplified mixture, butane, is not represented in system A4, so system selection
continues and system A8 is selected because it has the highest value of fitness (10,285 9).
— The fourth component in the simplified mixture is methane and this is already represented in systems

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A4 and A8, so no ternary mixture is selected.
— Selection is repeated with the first component in the simplified mixture, propane, and ternary system A7 is
selected because it has the next highest value of fitness (9,626 3; system A4 has already been selected).
All components in the simplified mixture are now represented in at least two of the ternary systems selected and
the selection process ends. The systems selected are therefore: A4, A7 and A8.
6.1.3 Sub-division of the inert-free mixture into the selected partial mixtures
The simplified mixture is divided into the selected partial ternary mixtures. A preliminary division of the
simplified mixture is made by assigning each component equally between the ternary systems in which it is
represented.
In the case of example 1, three ternary systems – A4, A7 and A8 – are selected. The preliminary division is
made by assigning methane equally between A4, A7 and A8; ethane equally between A4 and A8; propane equally
between A4 and A7; and butanes equally between A7 and A8 (Columns 4, 6 and 8).
6.1.4 Calculation of the methane number of the partial mixtures
The methane number of each partial mixture is calculated from Formula (3).
i=7 j=6
ij
MN = ax y (3)
()
ti∑∑ ,j
i=0 j=0
Where x and y are the volume fractions of the first and second components in each partial ternary mixture,
expressed as a percentage. In order to calculate the methane number of each partial mixture, therefore, the
composition of each is normalized to 100 %.
In the case of example 1 the composition of each partial mixture is calculated by renormalizing to 100 %
(Columns 5, 7 and 9).
Table A.2 lists the values of coefficients ai, j for the partial ternary systems A1–A18.
In the case of example 1 application of Formula (3) for each preliminary composition of partial mixture results in
calculated methane numbers of 76,248 9, 77,378 8 and 71,971 2 for A4, A7 and A8 respectively (Columns 5, 7 and 9).
6.1.5 Criteria for not using ternary systems for final calculation of the MNc
The MN from a partial ternary system does not match with the “target MN”. The “target MN” is the temporary
(during optimization) arithmetic average of all MNs calculated from each partial ternary system weighted
according to the volume content of the ternary system from the total gas composition.
st
Example There are three ternary systems selected, 1 system has 80 % of the quantity of the gas components,
nd rd st nd rd
2 has 15 %, 3 has 5 %. The calculated MNs are 1 70,3, 2 70,2, 3 70,0. Therefore the “target MN” results in:
(70,3⋅0,8 + 70,2⋅0,15 + 70,0⋅0,05) = 70,27
The content in the ternary systems that are not used during optimization is less than 0,05 % of the total
quantity of the gas components in the composition.
6.1.6 Adjustment of the composition and fraction of the partial mixtures
The composition and fraction (Ft) of each partial mixture is adjusted iteratively by varying the quantity of
each component in each partial mixture so as to minimize the difference between the methane numbers of
each partial mixture.
The value to be minimized is therefore:
(MNmax – MNmin),
oSIST prEN ISO 17507-1:2024
ISO/DIS 17507-1:2024(en)
where MNmax and MNmin are the maximum and minimum methane numbers for the selected partial
mixtures.
In the case of example 1, three ternary partial mixtures are selected and hence there are nine quantities to
be determined, however four of these can be obtained by material balance considerations.
NA8, methane = Nmethane – NA4, methane – NA7, methane
NA8, ethane = Nethane – NA4, ethane
NA7, propane = Npropane – NA4, propane
NA8, butane = Nbutane – NA7, butane
Where Nt, comp is the quantity of the respective component in partial mixture t.
The composition and fraction of each partial mixture is therefore performed by adjustment of five quantities: the
quantities of methane, ethane and propane in A4, and the quantity of methane and butane in A7.
During adjustment the volume fraction of any component in any partial mixture shall be within the range
for which the coefficients of Formula (3) are valid. Table A.2 lists the ranges of validity.
The problem of adjusting the composition and fraction of each partial mixture is therefore a constrained
minimization one and in principle any appropriate numerical procedure can be employed. For the examples
described in Annex A, the Solver supplied with Microsoft Excel® (using default settings) produces an
acceptable solution.
Depending upon the ending criterion of the numerical method employed, slight differences in the value of
(MNmax – MNmin) will result in slightly different values of methane number of the simplified mixture. In
addition, the use of different starting values for the composition and fraction of each partial mixture will
result in slightly different values of methane number of the simplified mixture. These differences are within
the uncertainties of this method, and it is recommended that the final value of methane number is rounded
to zero decimal places before reporting.
In the case of example 1, the composition and fraction of partial mixtures is provided in Table A.5 (Columns 4 –
9). For clarity, the five adjusted quantities are shown in underlined text.
6.1.7 Calculation of the methane number of the simplified mixture
The methane number of the simplified mixture is determined from the weighted average of the methane
number of the relevant partial ternary mixtures:
tN=
sys
′
MN =⋅()MN F (4)
∑ tt
t=1
where
MN′ is the methane number of the simplified mixture;
MN is the methane number of partial mixture t;
t
F is the fraction of the partial mixture t;
t
N is the number of ternary systems selected.
sys
In the case of example 1, this results in a methane number of the simplified mixture of MN′= 74,950 6.

oSIST prEN ISO 17507-1:2024
ISO/DIS 17507-1:2024(en)
6.1.8 Calculation of the methane number of the gaseous fuel
The methane number of the gaseous fuel is calculated by correcting the methane number of the simplified
mixture to allow for the presence of inerts in the original gaseous fuel:
MN = MN′+ MNinerts – MNmethane (5)
[1]
In the original work of AVL MNinerts is the methane number of a methane-carbon dioxide–nitrogen
mixture having the same inerts content as that of the original mixture. However, in the amendment of MWM
the MNinerts is calculated for a methane-carbon dioxide-nitrogen mixture containing only carbon dioxide
and methane. MNmethane is calculated for a methane-carbon dioxide-nitrogen mixture containing pure
methane and is equal to 99,998 0.
The methane number of the methane-carbon dioxide-nitrogen mixture is calculated using Formula (3).
Table A.2 lists the appropriate coefficients (system A20).
In the case of example 1, the methane-carbon dioxide-nitrogen mixture in volume fractions comprises
methane (97,875 0 %, the sum of the volumes of combustible components in the simplified mixture), nitrogen
(1,040 0 %) and carbon dioxide (1,460 0 %) (Table A.5, column 10), which is normalized to a nitrogen-free
mixture comprising methane (98,530 2 %) and carbon dioxide (1,469 8 %) (Table A.5, column 11). Application
of Formula (3) results in a methane number of MNinerts =101,360 0. Application of Formula (5) results in a
methane number of the gaseous fuel of 74,950 6 + 101,360 0 – 99,998 0 = 76,312 6.
The value of methane number is reported as 76.
6.2 Example 2
6.2.1 Simplification of the composition of the gaseous fuel
This example illustrates the calculation for a biomethane gaseous fuel derived from anaerobic digestion that
has been enriched by addition of propane. The composition is shown in Table A.6.
In the case of example 2 the quantity of butanes
= 0,146 1 + 0,029 2 · 2,3 + 0,000 0 · 5,3
= 0,213 3 (Column 2)
The simplified mixture is then re-normalized to 100 % (Column 3).
6.2.2 Calculation of fitness of the ternary systems
Application of Formula (1) to example 2 results in the values of Wj shown in Table A.7.
6.2.3 Selection of ternary mixtures
The first component in the simplified mixture is propane and this is present in ternary systems that have all
their components present in the simplified mixture – A2, A4, A7 and A8. In this case, A7 is selected because
it has the largest value of fitness (10,665 2).
The second component in the simplified mixture is ethane and this is not represen
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