Overview
ISO/TR 15409:2002 - Road vehicles - Heat rating of spark plugs is an informative Technical Report that documents established heat-rating methods for spark plugs used in spark‑ignition engines. Rather than prescribing a single mandatory test, the report summarizes multiple national and industry procedures (SAE, French, German, Japanese, U.K.) and explains terminology, measurement approaches and comparative techniques for assessing thermal behaviour, pre‑ignition and heat range of spark plugs.
Key topics
- Definitions and scope - Clear terms such as heat rating, heat‑rating value, heat‑rating identifier and heat range are defined to standardize communication across manufacturers and test labs.
- Heat‑rating methods - Methods covered include:
- The SAE heat‑rating method (Annex A) and the detailed SAE 17.6 cubic‑inch spark‑plug rating engine description (Annex B / SAE J2203). The report includes relevant test conditions such as nominal speed (~2700 rpm), compression ratio (5.6:1), spark advance (30° BTDC for non‑aviation), and environmental/fuel controls.
- Vehicle‑engine based procedures for measuring pre‑ignition and post‑ignition and/or temperature (Annex C).
- Comparative methods that rate candidate plugs against master spark plugs measured in either vehicle engines or the SAE engine (Annex D, E, F).
- Test parameters and operation - Examples of controlled variables given in the report include fuel composition, inlet air temperature and humidity, coolant/jacket temperatures, coolant flow and torque/IMEP calculation methods used to determine rating points.
- Informative annexes - Detailed national practices (SAE, French, German, Japanese, U.K.) are provided to facilitate comparison and correlation between different rating approaches.
Applications
- Quality control and production testing of spark plugs
- Comparative evaluation when designing or selecting plugs for a given engine application
- Research & development to optimize electrode/insulator designs for desired heat range and to minimize pre‑ignition or fouling
- Test-lab procedures for consistent, repeatable ratings and cross‑lab correlation
Who should use this report
- Spark plug and ignition equipment manufacturers
- Automotive test laboratories and OEM engine development teams
- Aftermarket product developers and suppliers
- Standards engineers and technical purchasing specialists seeking to compare rating data
Related standards
- ISO 2542:1980 - Internal combustion engines - Spark plug ignition - Terminology (referenced)
- SAE J549 / SAE J2203 (SAE practices referenced and summarized in annexes)
- Relevant military/fuel specs referenced in annex material (e.g., MIL‑L‑6082D)
ISO/TR 15409:2002 is a practical reference for anyone needing to understand or compare established spark‑plug heat‑rating practices across industry and national methods, helping ensure correct plug selection and reliable engine operation.