ISO 15501-2:2016

Road vehicles - Compressed natural gas (CNG) fuel systems - Part 2: Test methods

ISO 15501-2:2016 specifies the test methods for checking the minimum safety requirements specified in ISO 15501‑1. It is applicable to the functionality of the fuel systems designed to operate on compressed natural gas of motor vehicles as defined in ISO 3833.

Véhicules routiers — Systèmes d'alimentation en gaz naturel comprimé (GNC) — Partie 2: Méthodes d'essai

General Information

• Status: Published
• Publication Date: 07-Nov-2016
• ICS: 43.060.40 - Fuel systems
• Technical Committee: ISO/TC 22/SC 41 - Specific aspects for gaseous fuels
• Drafting Committee: ISO/TC 22/SC 41/WG 7 - General safety requirements for gaseous fuelled vehicles and terminology
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 01-Dec-2025
• Completion Date: 13-Dec-2025

Relations

• Revised: ISO 15501-2:2025 - Road vehicles - Compressed natural gas (CNG) fuel systems - Part 2: Test methods
• Effective Date: 18-Feb-2023
• Revises: ISO 15501-2:2001 - Road vehicles - Compressed natural gas (CNG) fuel systems - Part 2: Test methods
• Effective Date: 04-Nov-2015

Overview

ISO 15501-2:2016 specifies test methods for verifying the minimum safety requirements for compressed natural gas (CNG) fuel systems in road vehicles (as defined in ISO 3833). It is the Part 2 companion to ISO 15501‑1 (safety requirements) and focuses on practical tests for system functionality after installation, covering cylinder mounting strength, leak tightness, functional operation and receptacle mounting.

Key topics and technical requirements

• Cylinder mounting strength tests
  • Inertia (dynamic) test: cylinders mounted to vehicle/body or body part; cylinders filled to at least 90% of 20 MPa (200 bar) capacity (density 0.2 kg/l); trolley deceleration measured with channel frequency class CFC 60 (ISO 6487); deceleration maintained for ≥30 ms.
  • Static test: applies a traction force F = (M + 0.9 ρ V) a to the cylinder centre of gravity; force applied within 0.2 s, held ≥0.2 s.
  • Alternative methods: compliant crash tests or approved calculation methods may be accepted.
  • Acceptance: cylinders must remain attached and not interfere with seat structure; calculations require authority approval.
• Leak test
  • Per-vehicle test after installation at ambient temperature.
  • System upstream of the first-stage regulator pressurized at 1 MPa (10 bar) ±0.1 MPa and then 20 MPa (200 bar) ±1 MPa; inspect connections with gas detector or foam; no bubbles for 3 minutes or leak rate < 20 cm3/h.
• Functional tests
  • Main shut-off valve: must close when ignition is off, when engine stalls, when cranking on non‑CNG fuel, or when engine not running on CNG.
  • Receptacle clearance: verify free space conforms to ISO 15501‑1.
• Receptacle mounting tests
  • With service pressure applied, nozzle attached: apply 670 N axial pull and 200 N·m moment; gas tightness must be maintained.
• Annex A: engineering guidance for steel (Type 1) cylinder mountings, fastener/property recommendations and typical acceptable/ unacceptable arrangements.

Applications and users

ISO 15501-2 is used by:

• Vehicle OEMs and aftermarket converters for design validation and retrofit verification
• Test laboratories, notified bodies and regulatory authorities for certification and conformity assessment
• Installation engineers and fleet managers to ensure safe CNG cylinder anchoring, leak tightness and fuelling interface integrity
• Safety and compliance teams integrating CNG systems into passenger and commercial vehicles

Related standards

• ISO 15501-1 - Safety requirements for CNG fuel systems
• ISO 15500 series - CNG fuel system components
• ISO 11439 - High-pressure cylinders for on-board NG storage
• ISO 14469 - CNG refuelling connector
• ISO 6487 - Instrumentation for impact tests

Keywords: ISO 15501-2, CNG test methods, compressed natural gas fuel systems, cylinder mounting test, leak test, receptacle mounting, vehicle CNG safety.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 15501-2
Second edition
2016-11-15
Road vehicles — Compressed natural
gas (CNG) fuel systems —
Part 2:
Test methods
Véhicules routiers — Systèmes d’alimentation en gaz naturel
comprimé (GNC) —
Partie 2: Méthodes d’essai
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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the requester.
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test methods . 2
4.1 Cylinder mounting strength tests . 2
4.1.1 General. 2
4.1.2 Inertia test . 2
4.1.3 Static test . 2
4.1.4 Alternative method . 3
4.1.5 Acceptance criteria . 3
4.2 Leak test . 3
4.3 Functional test . 4
4.3.1 Main shut-off valve test . 4
4.3.2 Receptacle clearance test . 4
4.4 Receptacle mounting tests . 4
Annex A (informative) Engineering experience for the mounting of steel cylinders .5
Bibliography . 9
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
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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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions 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 the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 22, Road vehicles, Subcommittee SC 41, Specific
aspects for gaseous fuels.
This second edition cancels and replaces the first edition (ISO 15501-2:2001), which has been technically
revised.
A list of all parts in the ISO 15501 series can be found on the ISO website.
iv © ISO 2016 – All rights reserved

INTERNATIONAL STANDARD ISO 15501-2:2016(E)
Road vehicles — Compressed natural gas (CNG) fuel
systems —
Part 2:
Test methods
1 Scope
This document specifies the test methods for checking the minimum safety requirements specified in
ISO 15501-1. It is applicable to the functionality of the fuel systems designed to operate on compressed
natural gas of motor vehicles as defined in ISO 3833.
NOTE For tests of individual components, refer to the parts of ISO 15500, ISO 14469 and ISO 11439.
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 indicated applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 6487, Road vehicles — Measurement techniques in impact tests — Instrumentation
ISO 11439, Gas cylinders — High pressure cylinders for the on-board storage of natural gas as a fuel for
automotive vehicles
1)
ISO 15501-1:— , Road vehicles — Compressed natural gas (CNG) fuel systems — Part 1: Safety requirements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 15500-1, ISO 15501-1 and the
following 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
notified body
government appointed body mandated to approve or disapprove
EXAMPLE Laboratories, universities and companies.
1) Under preparation.
4 Test methods
4.1 Cylinder mounting strength tests
4.1.1 General
When a vehicle is equipped with several cylinders, they should preferably be tested as a unit.
When groups of cylinders are installed on a vehicle such that they are separately anchored to the
original structure of the vehicle, then each separate group of cylinders may be tested individually.
When performing these tests, accessories and piping shall not contribute to reinforcing the cylinder
mounting.
The requirements of ISO 15501-1:—, 4.4.3, shall be verified by the test specified in 4.1.2, 4.1.3, 4.1.4
or 4.1.5.
4.1.2 Inertia test
The cylinder or cylinders to be tested shall be mounted on the vehicle body or a part of the vehicle
body, according to the specifications of the original equipment manufacturer (OEM) or after-market
converter.
The vehicle body or part of the vehicle body shall be firmly anchored to the test trolley. The method
used for anchoring the vehicle body to the test trolley shall not result in reinforcement of the cylinder
anchorages or the part of the vehicle structure participating in anchoring the cylinder or cylinders.
Testing performed with a trolley
...