ISO 15501-2:2025

Overview

ISO 15501-2:2025 - Road vehicles - Compressed natural gas (CNG) fuel systems - Part 2: Test methods - specifies standardized test methods to verify the minimum safety and functional requirements given in ISO 15501-1 for vehicle CNG fuel systems. It applies to fuel systems fitted to motor vehicles as defined in ISO 3833 and covers system-level tests (cylinder mounting, leak, functional and receptacle mounting tests) rather than individual component qualification (see ISO 15500 series).

Key topics and technical requirements

• Cylinder mounting strength tests
  • Inertia test: cylinders mounted to the vehicle (or representative part) are filled (≥90% mass equivalent) and subjected to a specified deceleration profile measured with instrumentation conforming to ISO 6487 (CFC 60); deceleration must be maintained for at least 30 ms.
  • Static test: a traction force is applied to the cylinder centre of gravity and held; the force is defined by F = (M + 0,9 ρV) a where M = empty mass, V = cylinder volume and ρ = CNG density (document reference value).
  • Alternative methods: homologous crash tests or validated calculation methods may be accepted if equivalence is demonstrated.
  • Acceptance: cylinders shall remain attached to the vehicle structure and must not interfere with seat structures after testing. Annex A contains engineering guidance for steel (type 1) cylinder mountings (fastener sizes, reinforcement plates, clamping/retention practice).
• Leak test
  • Performed after system installation: pressurize upstream of the first-stage regulator to 1.0 MPa ±0.1 MPa, check all connections with gas detector or foam for the specified hold time, then repeat at service pressure. Any detected leaks must be repaired and the system re-tested.
• Functional tests
  • Main shut-off valve: verify the valve closes reliably when ignition is off, the engine stalls, cranking on non‑CNG fuel, or when the engine is not running on CNG.
  • Receptacle clearance: ensure free space around the fuelling receptacle conforms to ISO 15501-1 requirements.
• Receptacle mounting tests
  • With the nozzle connected and system at service pressure, apply a defined longitudinal pull (670 N) and a worst-case moment (200 N·m); gas tightness must not be impaired and shall be rechecked per the leak test.

Applications and who uses this standard

ISO 15501-2:2025 is intended for:

• OEM engineering teams designing CNG vehicle fuel systems
• After‑market converters and installers validating retrofit systems
• Test laboratories and conformity assessment bodies performing system-level safety tests
• Certification authorities, fleet operators and maintenance organizations requiring objective test methods for CNG systems

Use of ISO 15501-2 helps ensure consistent, reproducible verification of CNG system safety and functionality for vehicle certification, product validation and compliance.

Related standards

• ISO 15501-1:2025 (Safety requirements for CNG fuel systems)
• ISO 15500 series (CNG fuel system components)
• ISO 11439, ISO 14469 (component/cylinder standards)
• ISO 6487 (impact measurement instrumentation)
• ISO 3833 (vehicle classification/definitions)

Keywords: ISO 15501-2:2025, CNG fuel systems, test methods, cylinder mounting strength, leak test, receptacle mounting, road vehicles, compressed natural gas.