ISO 6518-1:2025

Road vehicles - Ignition systems - Part 1: Vocabulary

This document defines terms related to the ignition systems of spark-ignited internal combustion, mainly but not solely intended for use in road vehicles.

Véhicules routiers — Systèmes d'allumage — Partie 1: Vocabulaire

L'ISO 6518-1:2002 définit les termes relatifs aux systèmes d'allumage des moteurs à combustion interne à allumage par étincelle pour utilisation dans les véhicules routiers.

General Information

• Status: Published
• Publication Date: 25-Mar-2025
• ICS: 01.040.43 - Road vehicle engineering (Vocabularies)
• ICS: 43.060.50 - Electrical and electronic equipment. Control systems
• Technical Committee: ISO/TC 22/SC 32 - Electrical and electronic components and general system aspects
• Drafting Committee: ISO/TC 22/SC 32 - Electrical and electronic components and general system aspects
• Current Stage: 6060 - International Standard published
• Start Date: 26-Mar-2025
• Due Date: 28-Jun-2025
• Completion Date: 26-Mar-2025

Relations

• Revises: ISO 6518-1:2002 - Road vehicles - Ignition systems - Part 1: Vocabulary
• Effective Date: 02-Jul-2022

Overview

ISO 6518-1:2025 - Road vehicles - Ignition systems - Part 1: Vocabulary is the fourth edition vocabulary standard that defines terms used for ignition systems of spark‑ignited internal combustion engines, primarily for road vehicles. The document standardizes names and definitions for ignition system types, coil designs, electrical parameters, spark energy metrics, heat‑rating of spark plugs, and phenomena that cause uncontrolled engine ignition (for example, pre‑ignition and LSPI). It replaces ISO 6518-1:2002 and aligns vocabulary with the companion test methods in ISO 6518-2.

Key Topics

The standard provides clear definitions for:

• Types of ignition systems: inductive, capacitor discharge, semiconductor, breakerless, static/distributorless, current control and dwell control systems.
• Ignition coil types: single‑ended (including coil‑on‑plug), double‑ended, and multiple high‑tension assemblies.
• Electrical and timing parameters: secondary voltage (open‑circuit and available), maximum secondary output voltage, primary current and nominal primary interruption current, primary energy, primary inductance/leakage, dwell time/angle, feed‑forward voltage, primary clamp voltage, spark timing delay.
• Spark and discharge metrics: spark voltage/current, maximum spark current, spark duration, secondary spark energy, inductive spark energy, breakdown energy, Zener discharge parameters.
• Heat rating and heat range: definitions related to spark plug thermal performance, heat‑rating identifiers and cold fouling rating.
• Uncontrolled combustion terminology: self‑ignition, pre‑ignition (including low‑speed pre‑ignition - LSPI), and post‑ignition, with clarifying notes on measurement context.

Applications

ISO 6518-1:2025 is a foundational reference for consistency in documentation, design, testing and communication across the automotive and aftermarket sectors. Practical uses include:

• Harmonizing terminology in technical specifications, engineering reports and test procedures.
• Supporting calibration and design decisions for ignition coils, coil‑on‑plug systems, and electronic ignition modules by using standardized parameter names (e.g., dwell time, primary energy, ignition voltage reserve).
• Assisting test laboratories and OEMs to reference consistent definitions when applying the electrical performance and function test methods in ISO 6518-2.
• Reducing ambiguity in supplier contracts, regulatory filings, and international technical communication.

Who should use this standard

• Automotive engineers (powertrain and electrical)
• Ignition system and spark plug manufacturers
• Test laboratories and certification bodies
• Technical writers, standards committees and procurement teams

Related standards

• ISO 6518-2 - Road vehicles - Ignition systems - Part 2: Electrical performance and function test methods (companion document specifying test methods referenced by terms in Part 1).

Standards Content (Sample)

International
Standard
ISO 6518-1
Fourth edition
Road vehicles — Ignition systems —
2025-03
Part 1:
Vocabulary
Véhicules routiers — Systèmes d'allumage —
Partie 1: Vocabulaire
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Terms related to types of ignition coil . 2
5 Terms related to parameters . 3
6 Terms related to heat rating . 7
7 Terms related to phenomena leading to uncontrolled engine ignition . 7
Bibliography . 9
Index . 10

iii
Foreword
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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
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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 document 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)
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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 22, Road vehicles, Subcommittee SC 32,
Electrical and electronic components and general system aspects.
This fourth edition cancels and replaces the third edition (ISO 6518-1:2002), which has been technically
revised.
The main changes are as follows:
— modification of vocabulary according to revised ISO 6518-2.
A list of all parts in the ISO 6518 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.

iv
Introduction
The purpose of this document is to define terms related to the ignition systems of spark-ignited internal
combustion engines, mainly but not solely intended for use in road vehicles.
The test methods used to determine most of the parameters in Clause 5 are specified in ISO 6518-2.

v
International Standard ISO 6518-1:2025(en)
Road vehicles — Ignition systems —
Part 1:
Vocabulary
1 Scope
This document defines terms related to the ignition systems of spark-ignited internal combustion, mainly
but not solely intended for use in road vehicles.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
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
inductive ignition system
ignition system that stores its energy in an inductor or coil
3.1.1
classical ignition system
inductive ignition system (3.1) that uses an induction coil and breaker points with a capacitor in parallel
3.2
capacitor discharge ignition system
ignition system that stores its energy in a capacitor
3.3
semiconductor ignition system
ignition system that uses semiconductors for switching
3.3.1
semiconductor assisted ignition system
semiconductor ignition system (3.3) that uses breaker points
3.3.2
breakerless ignition system
semiconductor ignition system (3.3) that does not use breaker points
3.4
static ignition system
distributorless ignition system
ignition system that does not contain a rotating high-voltage distributor

3.4.1
static ignition system with single ended coil
static ignition system (3.4) which utilizes one ignition coil per cylinder, which serves the corresponding
cylinder only, the so-called single-ended coil(s) (4.1)
3.4.2
static ignition system with double-ended coil
static ignition system (3.4) which utilizes one ignition coil for two cylinders, the so-called double-ended coil(s) (4.2)
Note 1 to entry: This type of ignition system simultaneously produces a compression spark and an exhaust spark.
A compression spark is a spark occurring during the compression stroke of a cylinder. An exhaust spark is a spark
occurring during the exhaust stroke of a cylinder simultaneously with a spark occurring during the compression
stroke of another cylinder.
3.5
current control system
system combining the features of an inductive ignition system (3.1) and a breakerless ignition system (3.3.2),
and not excluding the features of a static ignition system (3.4), where the coil interruption current (5.10) is
maintained by a primary current sensing network at its design value over the widest practicable range of
primary supply voltage (5.31) and engine speed
3.6
dwell control system
system combining the features of an inductive ignition system (3.1) and a breakerless ignition system (3.3.2)
and not excluding the features of a static ignition system (3.4), where the control module is matched to
the ignition coil primary winding parameters (see 5.10 to 5.13) and the energizing interval is modified
by external factors such as primary supply voltage (5.31) and engine speed to give a primary interruption
current (5.10) between certain limits
4 Terms related to types of ignition coil
4.1
single-ended coil
ignition coil having one high-voltage terminal
4.1.1
coil on plug
plug-top coil
single-ended coil (4.1) directly mounted and connected to a spark plug
4.2
double-ended coil
ignition coil having a secondary winding, at each end of which is a high-voltage terminal
4.3
multiple high-tension terminal assembly
arrangement of ignition coils or windings providing multiple high-voltage terminals
4.3.1
multiple single-ended coil
multiple high-voltage terminal assembly formed of single-ended coils (4.1)
4.3.2
multiple double-ended coil
multiple high-voltage terminal assembly formed of double-ended coils (4.2)
4.3.3
multiple diode distribution coil
multiple high-voltage terminal assembly formed of coils having high-voltage terminals to each secondary winding

5 Terms related to parameters
5.1
secondary voltage
secondary output voltage
open circuit coil secondary voltage
U
s
voltage measured at the high-voltage terminal of the high-voltage source (coil output terminal without
loading)
5.2
maximum secondary output voltage
peak break down voltage
U
sm
maximum absolute value of the secondary output voltage (5.1)
5.3
available secondary voltage
available secondary spark voltage
U
av
voltage available at the spark plug terminal when the system is loaded by a capacitor
5.4
minimum available voltage
loaded secondary voltage
U
avm
minimum voltage available at the spark plug terminal when the system is loaded by a capacitor and a re
...