Hydrogen sampling is an essential part of ensuring reliable and accurate hydrogen fuel quality for expanding heavy-duty vehicle applications. Hydrogen sampling at refuelling stations is highly sensitive to operational conditions, especially temperature, pressure, storage homogeneity, and nozzle-purging procedures. The direct sampling method operates with a hydrogen fuelling station in maintenance mode and requires that parameters be set properly. This study investigated the impact of temperature, pressure, storage bank selection, and venting on hydrogen sample quality. This study shows that hydrogen sampling at refuelling stations is strongly influenced by operational parameters, with temperature and pressure mainly affecting the water content while other contaminants remain largely stable; storage bank composition and insufficient nozzle purging can also significantly bias results through contamination or non-representative sampling. To ensure reliable measurements, this study recommends conducting sampling under representative operational conditions, including matching the delivery temperature and nominal delivery pressure, verifying storage homogeneity, and applying adequate nozzle-purging procedures. However, further validation across different systems is still needed.

This study investigates how hydrogen refuelling station (HRS) operating parameters influence the representativeness of hydrogen fuel samples collected during parallel sampling events. Parallel sampling methodology is regularly used in Europe because it can be performed during normal vehicle refuelling with minimal disruption, but uncertainty remains regarding the effects of refuelling protocol, flow profile, or storage-bank usage. Experiments were conducted at the ZBT test HRS using the HySaM sampling system and at operating European HRS using the NPL ParSAM. Controlled comparisons were performed between several flow-rate profiles, while comprehensive impurity analysis was performed against ISO 14687:2025 requirements. Under controlled conditions, the refuelling protocol (excluding temperature and storage bank) and flow-rate profile had limited influence on most contaminants, whereas water showed the greatest variability and requires further investigation. However, repetitive sampling at normally operating HRS revealed larger differences for several species, including nitrogen, oxygen, argon, methane, carbon dioxide and sulphur, indicating that factors beyond protocol parameters tested in this study and nominal flow rate, such as storage-bank switching, flow path, and station hardware, may affect measured composition. Modelling indicates that the filling rates of the sampling cylinder and FCEV may diverge depending on the sampling-system strategy, highlighting the need for further improvements. The results show that parallel sampling may represent the fuel delivered during a specific refuelling event (if the filling rate of the cylinder and FCEV are sufficiently similar). However, parallel sampling may not fully represent the overall HRS and all operating conditions. Further research involving a broader range of HRS technologies and operating conditions may lead to validation and standardisation of the finding and possibly dedicated sampling protocols.

Hydrogen fuel quality is essential for the durability and reliability of fuel cell systems, particularly in heavy-duty (HD) vehicles operating under demanding conditions. Ensuring compliance with purity standards requires validated sampling systems at hydrogen refuelling stations. While established methods exist for light-duty (LD) refuelling, their suitability for HD applications has not been fully proven. This study evaluates three sampling systems (DirSAM, ENGIE sampler, and HySaM) through back-to-back HD refuelling experiments and comparison with LD configurations. Most gaseous impurities specified in ISO 14687:2025 showed statistical equivalence across systems within measurement uncertainties. Differences in nitrogen, water, and sulfur were system-dependent without consistent bias. LD sampling was found unreliable for representing HD conditions, particularly regarding water. No correlation was observed between particulate matter and dispensed hydrogen or vehicle state of charge. These results support adapting existing sampling methods to HD refuelling while highlighting the need for further validation and standard development.