Overview
ISO 21755-3:2025 - "Motorcycles - Measurement method for evaporative emissions - Part 3: VT‑SHED test procedure" specifies a standardized method for measuring evaporative emissions from motorcycles using the variable temperature sealed housing for evaporative determination (VT‑SHED). Applicable to motorcycles with spark‑ignition engines (four‑stroke, two‑stroke, or rotary piston), the standard defines the test sequence, equipment, calibration and result presentation for accurate assessment of fuel‑vapour losses such as diurnal breathing loss (DBL) and hot soak loss (HSL).
Key topics and technical requirements
- Scope and test structure: The VT‑SHED test comprises conditioning and test phases to simulate real‑world temperature variation and usage patterns.
- Test motorcycle and fuel: Vehicles should be run at least 1 000 km before testing; test fuel selection and vapour pressure must be agreed among parties and reported.
- Test sequence: Procedures include pre‑soaking, pre‑conditioning drive, fuel drain/refill steps, start soaking, carbon canister loading, dynamometer driving, hot soak loss (HSL) and diurnal breathing loss (DBL) measurements.
- Evaporative emission enclosure (VT‑SHED): A gas‑tight, hydrocarbon‑nonreactive chamber with controlled temperature profiling. The temperature control must follow the prescribed diurnal profile with an average tolerance of ±1 K and interior surface limits between 278.2 K and 328.2 K.
- Chassis dynamometer: Single‑roll dynamometer with roll diameter ≥ 0.400 m and roll revolution counter to measure distance; running resistance setup per ISO 11486.
- Analytical systems and calibration: Hydrocarbon analysers, pressure and temperature recording systems and chamber calibration (volume, background emissions, retention) are required. Clause 5 addresses calibration frequency and methods.
- Result calculation and reporting: Methods for calculating evaporative emission totals and standardized test reporting formats are defined.
Practical applications and users
ISO 21755-3:2025 is designed for:
- Motorcycle manufacturers performing design validation and production compliance testing.
- Independent test laboratories conducting certification and conformity assessment.
- Regulatory agencies defining evaporative emission limits and test protocols.
- R&D teams studying fuel system design, canister performance and fuel‑vapour mitigation strategies.
Typical uses include type‑approval testing, development of evaporative control systems (canisters, purge strategies), and comparative research into fuel vapour behavior under variable temperatures.
Related standards
This part is part of the ISO 21755 series and references other motorcycle testing standards, including:
Keywords: ISO 21755-3:2025, VT‑SHED, motorcycle evaporative emissions testing, diurnal breathing loss, hot soak loss, evaporative emission enclosure, chassis dynamometer, hydrocarbon analyser.