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