Abstract
The Federal Institute of Metrology METAS developed a Hydrogen Field Test Standard (HFTS) that can be used for field verification and calibration of hydrogen refuelling stations. The testing method is based on the gravimetric principle. The experimental design of the HFTS as well as the description of the method are presented here. The HFTS has been tested at METAS with nitrogen gas at −40 °C to mimic a refuelling process in the field. Laboratory tests have shown that icing on the pipes of the HFTS have a non-negligible impact on the results. Field-testing with the HFTS has also been performed at the Empa hydrogen refuelling station with hydrogen at up to 70 MPa. The major uncertainty components have been identified and assigned values. The required expanded uncertainty of 0.3% could be achieved. A detailed uncertainty budget has been presented and shows that the scale is the largest contributor; buoyancy corrections only play a minor role. For the lowest uncertainty measurements, appropriate waiting times or cleaning methods to get rid of icing are required.
Highlights
A large hydrogen infrastructure is currently in development across Europe
The maximum fuel flow rate, the rate of pressure increase and the ending pressure are all parameters that are defined by process limits and are affected by ambient temperature, fuel delivery temperature and initial pressure in the vehicle’s hydrogen tank
Mass flow is determined by a pressure-ramp rate (PRR) that depend on initial pressure, available volume and temperature
Summary
A large hydrogen infrastructure is currently in development across Europe. The industry faces the dilemma that they are required to meet certain measurement requirements set by legislation that currently cannot be followed due to the lack of available methods and standards. We are far from steady conditions and only limited studies of high pressure hydrogen flow meters under transient conditions have been performed [2,3]. International requirements propose accuracies for meters used in hydrogen refuelling station [4] and only very limited studies have been performed on how to test, inspect and verify such systems under labo ratory conditions and in the field. Standards for field verification as well as an investigation into the use of substitute fluids for laboratory testing or calibration of flow meters used in hydrogen refuelling stations (HRS). We constructed a Hydrogen Field Test Standard certified for measurements in an environment with explosive atmosphere and performed measurements in the laboratory using nitrogen gas cooled down to À 40 C to mimic real conditions as encountered in a HRS. The required expanded uncertainty of 0.3% could be achieved and field-testing with hydrogen confirmed the laboratory results
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