Natural gas - Natural gas for use as a compressed fuel for vehicles - Part 1: Designation of the quality (ISO 15403-1:2006)

The aim of ISO 15403-1:2006 is to provide manufacturers, vehicle operators, fuelling station operators and others involved in the compressed-natural-gas vehicle industry with information on the fuel quality for natural gas vehicles (NGVs) required to develop and operate compressed-natural-gas vehicle equipment successfully.
Fuel meeting the requirements of ISO 15403-1:2006 should provide for the safe operation of the vehicle and associated equipment needed for its fuelling and maintenance, protect the fuel system from the detrimental effects of corrosion, poisoning, and liquid or solid deposition and provide satisfactory vehicle performance under any and all conditions of climate and driving demands.
Some aspects of ISO 15403-1:2006 may also be applicable for the use of natural gas in stationary combustion engines.

Erdgas - Erdgas als verdichteter Kraftstoff für Fahrzeuge - Teil 1: Bestimmung der Beschaffenheit (ISO 15403-1:2006)

Ziel dieses Teils von ISO 15403 ist die Bereitstellung von Daten zur Beschaffenheit von Kraftstoff für Erdgas-fahrzeuge (NGV), die Hersteller, Fahrzeugbetreiber, Tankstellenbetreiber und andere Beteiligte der Industrie für mit verdichtetem Erdgas angetriebene Fahrzeuge benötigen, um Geräte für diese Fahrzeuge erfolgreich zu entwickeln und zu betreiben.
Kraftstoff, der die Anforderungen dieses Teils von ISO 15403 erfüllt, sollte:
a)   den sicheren Betrieb des Fahrzeugs und damit verbundener Geräte für Kraftstoffversorgung und Instandhaltung gewährleisten;
b)   das Kraftstoffsystem vor den schädlichen Einflüssen von Korrosion, Vergiftung sowie der Ablagerung von flüssigen und festen Stoffen schützen;
c)   eine zufriedenstellende Leistung des Fahrzeugs unter allen klimatischen Bedingungen und Fahr-erfordernissen gewährleisten.
Einige Aspekte dieses Teils von ISO 15403 können ebenfalls für die Anwendung auf Erdgas in ortsfesten Verbrennungsmotoren zutreffen.

Gaz naturel - Gaz naturel pour usage comme carburant comprimé pour véhicules - Partie 1: Désignation de la qualité (ISO 15403-1:2006)

L'ISO 15403-1:2006 a pour objet de fournir aux constructeurs, aux exploitants de parcs automobiles, aux responsables de stations de remplissage et à tous ceux qui sont impliqués dans l'industrie des véhicules roulant au gaz naturel comprimé les informations qui leur sont nécessaires sur la qualité du carburant alimentant les véhicules ainsi que les équipements automobiles conçus pour fonctionner avec du gaz naturel comprimé.
Les carburants respectant les exigences de l'ISO 15403-1:2006 sont censés assurer un fonctionnement en toute sécurité du véhicule et des équipements qui lui sont associés pendant le remplissage et en maintenance, protéger l'installation des effets nocifs de la corrosion, de la contamination et des dépôts liquides ou solides, et garantir un fonctionnement satisfaisant du véhicule dans toutes les conditions climatiques et quelles que soient les sollicitations que lui fait subir le conducteur.
Des aspects abordés dans l'ISO 15403-1:2006 peuvent également être applicables à l'utilisation du gaz naturel dans les moteurs stationnaires à combustion interne.

Zemeljski plin - Zemeljski plin, ki se uporablja za komprimirano gorivo za vozila - 1. del: Označevanje kakovosti (ISO 15403-1:2006)

General Information

Status
Published
Publication Date
08-Jan-2008
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
09-Jan-2008
Completion Date
09-Jan-2008

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SLOVENSKI STANDARD
SIST EN ISO 15403-1:2008
01-marec-2008

=HPHOMVNLSOLQ=HPHOMVNLSOLQNLVHXSRUDEOMD]DNRPSULPLUDQRJRULYR]DYR]LOD

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Natural gas - Natural gas for use as a compressed fuel for vehicles - Part 1: Designation

of the quality (ISO 15403-1:2006)
Gaz naturel - Gaz naturel pour usage comme carburant comprimé pour véhicules -
Partie 1: Désignation de la qualité (ISO 15403-1:2006)
Ta slovenski standard je istoveten z: EN ISO 15403-1:2008
ICS:
75.060
SIST EN ISO 15403-1:2008 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
EUROPEAN STANDARD
EN ISO 15403-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
January 2008
ICS 75.060
English Version
Natural gas - Natural gas for use as a compressed fuel for
vehicles - Part 1: Designation of the quality (ISO 15403-1:2006)
Gaz naturel - Gaz naturel pour usage comme carburant
comprimé pour véhicules - Partie 1: Désignation de la
qualité (ISO 15403-1:2006)
This European Standard was approved by CEN on 15 December 2007.

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 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 Management Centre has the same status as the

official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,

Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15403-1:2008: E

worldwide for CEN national Members.
---------------------- Page: 2 ----------------------
EN ISO 15403-1:2008 (E)
Foreword

The text of ISO 15403-1:2006 has been prepared by Technical Committee ISO/TC 193 "Natural

gas” of the International Organization for Standardization (ISO) and has been taken over as EN

ISO 15403-1:2008 by Technical Committee CEN/SS N21 "Gaseous fuels and combustible gas",

the secretariat of which is held by CMC.

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 July 2008, and conflicting national

standards shall be withdrawn at the latest by July 2008.

Attention is drawn to the possibility that some of the elements of this document may be the

subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any

or all such patent rights.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of

the following countries are bound to implement this European Standard: Austria, Belgium,

Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece,

Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United

Kingdom.
Endorsement notice

The text of ISO 15403-1:2006 has been approved by CEN as EN ISO 15403-1:2008 without any

modifications.
---------------------- Page: 3 ----------------------
INTERNATIONAL ISO
STANDARD 15403-1
First edition
2006-10-15
Natural gas — Natural gas for use
as a compressed fuel for vehicles —
Part 1:
Designation of the quality
Gaz naturel — Gaz naturel pour usage comme carburant comprimé
pour véhicules —
Partie 1: Désignation de la qualité
Reference number
ISO 15403-1:2006(E)
ISO 2006
---------------------- Page: 4 ----------------------
ISO 15403-1:2006(E)
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© ISO 2006

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
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Published in Switzerland
ii © ISO 2006 – All rights reserved
---------------------- Page: 5 ----------------------
ISO 15403-1:2006(E)
Contents Page

Foreword............................................................................................................................................................ iv

Introduction ........................................................................................................................................................ v

1 Scope ......................................................................................................................................................1

2 Normative references ............................................................................................................................1

3 Terms and definitions ...........................................................................................................................1

4 Symbols and abbreviations ..................................................................................................................9

5 Gas composition requirements..........................................................................................................10

6 Gas properties......................................................................................................................................11

7 Driveability............................................................................................................................................12

8 Test methods........................................................................................................................................12

9 Sampling...............................................................................................................................................13

Annex A (informative) Propane and butane content .....................................................................................14

Annex B (informative) Wobbe index range.....................................................................................................16

Annex C (informative) Engine knock...............................................................................................................18

Annex D (informative) Methane number and octane number.......................................................................19

Annex E (informative) Water content of natural gas......................................................................................22

Bibliography ......................................................................................................................................................23

© ISO 2006 – All rights reserved iii
---------------------- Page: 6 ----------------------
ISO 15403-1:2006(E)
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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 15403-1 was prepared by Technical Committee ISO/TC 193, Natural gas.

This first edition of ISO 15403-1 cancels and replaces ISO 15403:2000, of which it constitutes a minor revision

including the following changes:
⎯ correction of the title to reflect that ISO 15403 is now formed of two parts;

⎯ reformat the document in accordance with the ISO/IEC Directives, Part 2, Fifth edition, 2004;

⎯ reformat the references cited in Clause 2 and in the Bibliography, in accordance with the ISO/IEC

Directives, Part 2, Fifth edition, 2004.

ISO 15403 consists of the following parts, under the general title Natural gas — Natural gas for use as a

compressed fuel for vehicles:
⎯ Part 1: Designation of the quality
⎯ Part 2: Specification of the quality (Technical Report)
iv © ISO 2006 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 15403-1:2006(E)
Introduction

Natural gas has been used to some extent as a fuel for internal combustion engines in compressor stations,

co-generation systems, and vehicles of various types for many years now. However, the prerequisites for

growth, i.e. economic viability and fuel availability, were generally not satisfied. Now, with the natural gas

industry well established, supplying 20 % of the world's primary energy, and the need for alternative, low-

emission fuels, the situation has improved considerably. During the past decade, natural gas vehicles have

become a viable option with some five millions units now in use around the world. Growth is continuing as

many governments actively promote this clean-burning fuel with its environmental benefits. Many fleet

operators are converting their vehicles, and vehicle manufacturers are developing and marketing dedicated

natural gas equipment.

In the context of this International Standard, natural gas vehicles (NGVs) utilize compressed natural gas

stored “on-board”. The pressure of the gas stored in multiple containers is up to a maximum 25 000 kPa.

Although the pressure has to be reduced before combustion, compression and storage gives NGVs an

adequate range. While NGVs were initially equipped with converted gasoline or diesel engines, high-

performance, dedicated natural gas engines are now being extensively developed and produced. Liquefied

natural gas (LNG) may also be stored in the fuel tanks of natural gas vehicles. This, however, will be the

subject of a separate International Standard.

This part of ISO 15403 for the quality designation of compressed natural gas is designed to stipulate the

international requirements placed on the natural gas used as a motor fuel. Engine and vehicle manufacturers

must know these requirements so they can develop high-performance equipment which runs on compressed

natural gas.

A technical report giving detailed data on the gas compositions used in this part of ISO 15403 is being

published as ISO/TR 15403-2.
© ISO 2006 – All rights reserved v
---------------------- Page: 8 ----------------------
INTERNATIONAL STANDARD ISO 15403-1:2006(E)
Natural gas — Natural gas for use as a compressed fuel
for vehicles —
Part 1:
Designation of the quality
1 Scope

The aim of this part of ISO 15403 is to provide manufacturers, vehicle operators, fuelling station operators and

others involved in the compressed-natural-gas vehicle industry with information on the fuel quality for natural

gas vehicles (NGVs) required to develop and operate compressed-natural-gas vehicle equipment successfully.

Fuel meeting the requirements of this part of ISO 15403 should

a) provide for the safe operation of the vehicle and associated equipment needed for its fuelling and

maintenance;

b) protect the fuel system from the detrimental effects of corrosion, poisoning, and liquid or solid deposition;

c) provide satisfactory vehicle performance under any and all conditions of climate and driving demands.

Some aspects of this part of ISO 15403 may also be applicable for the use of natural gas in stationary

combustion engines.
2 Normative references

The following referenced documents are indispensable for the application 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 6976:1995, Natural gas — Calculation of calorific values, density, relative density and Wobbe index from

composition
3 Terms and definitions

For the purposes of this document, the following terms and definitions apply. Definitions were taken from

ISO 14532 whenever possible.
3.1
natural gas

complex mixture of hydrocarbons, primarily methane, but generally also including ethane, propane and higher

hydrocarbons in much smaller amounts and some non-combustible gases, such as nitrogen and carbon

dioxide
NOTE 1 Natural gas generally also includes minor amounts of trace constituents.
© ISO 2006 – All rights reserved 1
---------------------- Page: 9 ----------------------
ISO 15403-1:2006(E)

NOTE 2 Natural gas is produced and processed from the raw gas or liquefied natural gas and, if required, blended to

the extent suitable for direct use (for example as gaseous fuel).

NOTE 3 Natural gas remains in the gaseous state under the temperature and pressure conditions normally found in

service.

NOTE 4 Natural gas consists predominantly of methane (mole fraction greater than 0,70), and has a superior calorific

3 3

value normally within the range 30 MJ/m to 45 MJ/m . It contains also ethane (typically up to 0,10 mole fraction), propane,

butanes and higher alkanes in steadily decreasing amounts. Nitrogen and carbon dioxide are the principal non-

combustible components, each present at levels which typically vary from less than 0,01 mole fraction to 0,20 mole

fraction.

Natural gas is processed from the raw gas so as to be suitable for use as industrial, commercial, residential fuel or as a

chemical feedstock. The processing is intended to reduce the contents of potentially corrosive components, such as

hydrogen sulfide and carbon dioxide, and of other components, such as water and higher hydrocarbons, potentially

condensable in the transmission and distribution of the gas. Hydrogen sulfide, organic sulfur compounds and water are

then reduced to trace amounts, and high carbon dioxide contents are likely to be reduced to below 0,05 mole fraction.

Natural gas is normally technically free from aerosol, liquid and particulate matter.

In some circumstances natural gas may be blended with town gas or coke oven gas, in which case hydrogen and carbon

monoxide will be present in amounts up to 0,10 mole fraction and 0,03 mole fraction respectively. In this case, small

amounts of ethylene may also be present.

Natural gas may also be blended with LPG1)/air mixtures, in which case oxygen will be present, and the levels of propane

and butanes will be considerably enhanced.

NOTE 5 Pipeline quality natural gas is one which has been processed so as to be suitable for direct use as industrial,

commercial, residential fuel or as a chemical feed stock.

The processing is intended to reduce the corrosive and toxicity effects of certain components, and to avoid condensation

of water or hydrocarbons in the transmission and distribution of the gas.

Hydrogen sulfide and water should only be present in trace amounts, and high carbon dioxide content is likely to be

reduced.
[ISO 14532:2001, 2.1.1.1]
3.2
substitute natural gas

manufactured or blended gas which is interchangeable in its properties with natural gas

[ISO 14532:2001, 2.1.1.3]
NOTE Manufactured gas is sometimes called synthetic natural gas.
3.3
compressed natural gas

natural gas used as a fuel for vehicles, typically compressed up to 20 000 kPa in the gaseous state

[ISO 14532:2001, 2.1.1.12]
NOTE The maximum pressure for natural gas stored in a container is 25 000 kPa.
3.4
gas quality

attribute of natural gas dependent on its composition and its physical properties

[ISO 14532:2001, 2.1.1.14]
1) LPG = liquefied petroleum gas.
2 © ISO 2006 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 15403-1:2006(E)
3.5
normal reference conditions

reference conditions of pressure, temperature and humidity (state of saturation) equal to: 101,325 kPa and

273,15 K for a real, dry gas
3.6
standard reference conditions

reference conditions of pressure, temperature and humidity (state of saturation) equal to: 101,325 kPa and

288,15 K for a real, dry gas

NOTE 1 Good practice requires that the reference conditions are incorporated as part of the symbol, and not of the unit,

for the physical quantity represented.
EXAMPLE
È ˘
Hp ,,T Vp ,T
Scrc crc mrc mrc
Î ˚
where
H superior calorific value on volumetric basis;
T temperature of the combustion reference conditions;
crc
p pressure of the combustion reference conditions;
crc

V(p , T ) volume at temperature and pressure of the metering reference conditions.

mrc mrc

NOTE 2 Standard reference conditions are also referred to as metric standard conditions.

NOTE 3 The abbreviation s.t.p. (standard temperature and pressure) replaces the abbreviation N.T.P. (Normal

Temperature and Pressure), as formerly used, and is defined as the condition of pressure and temperature equal to:

101,325 kPa and 288,15 K. No restriction is given on the state of saturation.
[ISO 14532:2001, 2.6.1.4]
3.7
superior calorific value

energy released as heat by the complete combustion in air of a specified quantity of gas, in such a way that

the pressure p at which the reaction takes place remains constant, and all the products of combustion are

returned to the same specified temperature T as that of the reactants, all of these products being in the

gaseous state except for water formed by combustion, which is condensed to the liquid state at T

NOTE 1 Where the quantity of gas is specified on a molar basis, the calorific value, expressed in MJ/mol, is designated

as:
H pT,
S1 1
On a mass basis the calorific value, expressed in MJ/kg, is designated as:
H pT,
S1 1

Where the quantity of gas is specified on a volumetric basis, the calorific value, expressed in MJ/m , is designated as:

È ˘
Hp,,TVp,T
S1 1 2 2
Î ˚
where p and T are the gas volume (metering) reference conditions.
2 2
© ISO 2006 – All rights reserved 3
---------------------- Page: 11 ----------------------
ISO 15403-1:2006(E)

The volumetric based calorific value should be specified to normal or standard reference conditions.

NOTE 2 The terms gross, higher, upper and total calorific value, or heating value, are synonymous with superior

calorific value.
NOTE 3 The calorific value should be specified to the combustion conditions.
NOTE 4 The calorific value is normally stated as dry.

EXAMPLE Hp ,T designates the superior calorific value, specified on a volumetric basis, at standard

S,w src src

reference conditions and stated as wet. For simplicity, the combustion conditions are not specified.

NOTE Adapted from ISO 14532:2001, 2.6.4.2.
3.8
inferior calorific value

energy released as heat by the complete combustion in air of a specified quantity of gas, in such a way that

the pressure p at which the reaction takes place remains constant, and all the products of combustion are

returned to the same specified temperature T as that of the reactants, all of these products being in the

gaseous state

NOTE 1 Superior calorific value differs from inferior calorific value by the heat of condensation of water formed by

combustion.

NOTE 2 Where the quantity of gas is specified on a molar basis, the calorific value, expressed in MJ/mol, is designated

as:
H pT,
I1 1
On a mass basis the calorific value, expressed in MJ/kg, is designated as:
H pT,
I1 1

Where the quantity of gas is specified on a volumetric basis, the calorific value, expressed in MJ/m3, is designated as:

È ˘
Hp,,TV p,T
I1 1 2 2
Î ˚
where p and T are the gas volume (metering) reference conditions.
2 2

NOTE 3 The terms net and lower calorific value, or heating value, are synonymous with inferior calorific value.

NOTE 4 Superior and inferior calorific values can also be stated as dry or wet (denoted by the subscript “w”) depending

on the water vapour content of the gas prior to combustion.

The effects of water vapour on the calorific values, either directly measured or calculated, are described in Annex F of

ISO 6976:1995.

NOTE 5 Normally the calorific value is expressed as the superior, dry value specified on volumetric basis under normal

or standard reference conditions.
[ISO 14532:2001, 2.6.4.2]
4 © ISO 2006 – All rights reserved
---------------------- Page: 12 ----------------------
ISO 15403-1:2006(E)
3.9
density

mass of gas divided by its volume at specified conditions of pressure and temperature

NOTE In a mathematical representation the density is given by:
r pT, =
Vp,T
[ISO 14532:2001, 2.6.3.1]
3.10
relative density

quotient of the mass of a gas, contained within an arbitrary volume, and the mass of dry air of standard

composition (defined in ISO 6976:1995) which would be contained in the same volume at the same reference

conditions

NOTE 1 An equivalent definition is given by the ratio of the density of the gas ρ to the density of dry air of standard

composition ρ at the same reference conditions.
r pT,
( )
g src src
d =
r pT,
a src src
where
p is the pressure at standard reference conditions;
src
T is the temperature at standard reference conditions;
src

ρ(p , T ) is the mass volume at the standard-temperature and standard-pressure conditions

src src
NOTE 2 Density can be expressed in terms of the real gas law:
M◊ p
r =
Z◊◊RT

With this relation the relative density, when both gas and air are considered as real fluids, becomes:

Mp◊
gsrc
Zp,,T ◊◊RT M◊Z p T
() ()
g src src src g a src src
d==
Mp◊
MZp◊ ,T
asrc
ag src src
Zp ,T ◊◊RT
a src src src

For ideal gas behaviour of the gases, when both gas and air are considered as fluids which obey the ideal gas law, the

relative density becomes:
d =

NOTE 3 In former times, the above ratio M /M was called specific gravity of a gas, which has the same value as the

g a

relative density if ideal behaviour of the gases is assumed. The term relative density should now replace the term specific

gravity.
[ISO 14532:2001, 2.6.3.2]
© ISO 2006 – All rights reserved 5
---------------------- Page: 13 ----------------------
ISO 15403-1:2006(E)
3.11
Wobbe index

calorific value, on a volumetric basis, at specified reference conditions, divided by the square root of the

relative density at the same specified metering reference conditions
NOTE 1 The volume is stated at normal or standard reference conditions.

NOTE 2 The Wobbe index is specified as superior (denoted the subscript “S”) or inferior (denoted the subscript “I”),

depending on the calorific value, and as dry or wet (denoted by the subscript “w”) depending on the calorific value and the

corresponding density.
EXAMPLE

Wobbe index, superior, specified on a volumetric basis, at standard reference conditions and stated as wet (denoted by

the supscript “w”)
Hp ,T
S,w src src
Wp ,T =
Ssrc src
dp ,T
wsrc src

NOTE 3 The Wobbe index is a measure of heat input to gas appliances derived from the orifice flow equation. Heat

input for different natural gas compositions is the same if they have the same Wobbe index, and operate under the same

gas pressure (see ISO 6976).
NOTE Adapted from ISO 14532:2001, 2.6.4.4.
3.12
compression factor

quotient of the actual (real) volume of an arbitrary mass of gas, at a specified pressure and temperature, and

the volume of the same gas, under the same conditions, as calculated from the ideal gas law

NOTE 1 The terms «compressibility factor» and «Z-factor» are synonymous with compression factor.

NOTE 2 The formula for the compression factor is as follows:
V (real)
Z =
V (ideal)
where
R◊T
V (ideal) =
Thus
p ⋅Vy()
Zp(,T,y) =
R ⋅T
where
p absolute pressure;
T thermodynamic temperature;
y set of parameters which uniquely characterizes the gas;
V molar volume;
R molar gas constant in coherent units;
Z compression factor.
6 © ISO 2006 – All rights reserved
---------------------- Page: 14 ----------------------
ISO 15403-1:2006(E)
[1]

In principle, y may be the complete molar composition (see ISO 12213-2 ) or a distinctive set of dependent physico-

[2]
chemical properties (see ISO 12213-3 ).

NOTE 3 Compression factor is a dimensionless quantity usually close to unity near standard or normal reference

conditions. Within the range of pressures and temperatures encountered in gas transmission, compression factor can

significantly differ from unity.

NOTE 4 The supercompressibility factor is defined as the square root of the ratio of the compression factor at reference

conditions to the compression factor of the same gas at the conditions of interest:

f =
Z(,pT,y)
where
Z is the compression factor at base conditions of pressure and temperature.

Base conditions are temperature and pressure conditions at which natural gas volumes are determined for purpose of

custody transfer. In natural gas measurements the properties of interest are temperature, pressure and composition.

Assuming ideal gas properties, for simplicity, tables of pure compounds can be prepared for use in calculating gas

properties for any composition at “base conditions”. These “base conditions” are chosen near ambient.

In the IGU Dictionary of the Gas Industry the supercompressibility factor is defined as:

f =
Z()pT,,y

The supercompressibility factor is used with measurements made by flow instruments. The volume obtained with a flow

meter must be multiplied by “f” to obtain the corrected volume.

The compression factor is used with measurements made by displacement methods. In this case the volume must be

multiplied by “1/Z” to obtain the correct volume.
[ISO 14532:2001, 2.6.2.2]
3.13
water dew point
temperature above which no condensation of water occurs at a specified pressure

NOTE For any pressure lower than the specified pressure there is no condensation at this dew-point temperature.

[ISO 14532:2001, 2.6.5.1.1]
3.14
hydrocarbon dew point

temperature above which no condensation of hydrocarbons occurs at a specified pressure

NOTE 1 At a given dew point temperature there is a pressure range within which condensation occurs because of

retrograde behaviour. The cricondentherm defines the maximum temperature at which condensation can occur.

NOTE 2 The dew point line is the locus of pressure and temperature points which separate the single phase gas from

the gas-hydrocarbon liquid region.
[ISO 14532:2001, 2.6.5.2.1]
© ISO 2006 – All rights reserved 7
---------------------- Page: 15 ----------------------
ISO 15403-1:2006(E)
3.15
molar composition

proportion of each component expressed as a molar (or mole) fraction, or molar (mole) percentage, of the

whole

NOTE 1 Thus the mole fraction, x , of component i is the quotient of the number of moles of component i and the

number of moles of the whole mixture present in the same arbitrary volume. One mole of any chemical species is the

amount of sub-stance which has the relative molecular mass in grams. A table of recommended values of relative

molecular masses is given in ISO 6976:1995.

NOTE 2 For an ideal gas, the mole fraction (or percentage) is identical to the volume fraction (percentage), but this

relationship cannot in general be assumed to apply to real gas behaviour.
3.16
gas composition

fractions or percentages of the main components, associated components, trace components and other

components determined from natural gas analysis
NOTE Adapted from ISO 14532:2001, 2.6.6.1.
3.17
odorization
addition of odorants, normally
...

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