Metrology for Hydrogen Vehicles

Patrick Stadelmann, Empa

17. September 2019

Outline

1. Introduction

2. Testing device to determine accuracy of meters and dispensers

3. Test campaign of hydrogen filling stations in operation

4. Preliminary conclusions and recommendations

Outline

1. Introduction

2. Testing device to determine accuracy of meters and dispensers

3. Test campaign of hydrogen filling stations in operation

4. Preliminary conclusions and recommendations

Background on hydrogen flow metering

Hydrogen supplied can vary up to 875

bar in pressure and between -40°C to

ambient temperature during refuelling

Unknown mass of

hydrogen is lost

during venting

Flow meters in the

refuelling station

must be accurate to

1% (OIML R 139-1)

Refuelling stations

cannot cost their

customers with

required accuracies

Background on hydrogen flow metering

• Up to now the sale of H2 without certified flow meter is tolerated by the authorities

(demonstration projects, limited group of users)

o By entering the commercial phase with extension of the HRS network, uncalibrated sales of

H2 cannot be tolerated anymore

• Until beginning of 2018, no certified reference testing device in Europe to

determine the global accuracy → of meters and dispenser

Hydrogen accuracy classes

• Revision of the OIML R139 standard for gaseous dispenser

o New version approved and published in Oct 2018

o Accuracy classes have been largely discussed and revised:

→ Class 2 & Class 4 have been created for hydrogen service

→ In principle Class 2 is accepted for future stations, whereas Class 4 is tolerated for existing stations

Note: Class 4 seems to be tolerated in France for a limited period only

Outline

1. Introduction

2. Testing device to determine accuracy of meters and dispensers

3. Test campaign of hydrogen filling stations in operation

4. Preliminary conclusions and recommendations

Hydrogen field test standard

• Testing device designed and manufactured by Air Liquide and Metas

Air Liquide reference testing device Metas reference testing device

Design of METAS testing device

Composite tanks

Housing (ESD plastic)

Hydraulic system

High precision scale

Design of METAS testing device

• Main characteristics

o High precision scale: resolution 0.05g, Ex-certified

o Composite tank of 2x36L (i.e. 3.0 kg of H2 at 700 bar, 15°C)

o Mobile test bench to be moved on each HRS

o Housing (ESD plastic) as protection against wind:

o Stable measurements, even with wind conditions

o Several nozzles to flood the housing with inert gas to limit

possible ice build up

o Improved depressurization system:

o Depressurization time (from 700 to 20 bar): 1h30 to 1h45

o Possibility to lift the frame from the scale for transport

o Valve panel to inert tank with N2 for transport

Design of METAS testing device

Outline

1. Introduction

2. Testing device to determine accuracy of meters and dispensers

3. Test campaign of hydrogen filling stations in operation

4. Preliminary conclusions and recommendations

Specific constraints

• Installation on site:

o Trailer must not move for the whole test campaign

o HRS must remain accessible for car fueling

o Preparation work ahead on HRS layouts

o Safety issues must be taken into account (safety

perimeter)

• Needs / Data recording

o Electrical power for the scale

o Nitrogen bundle/bottles

o Data expected from the HRS

Tests performed

• Accuracy tests

o Series of tests:

o 1 full fillings 20-700 bar Automatic stop

o 1 partial fillings 20-350 bar Manual stop

o 1 partial fillings 350-700 bar Automatic stop

o 4 MMQ fillings (1kg) with different starting pressure (450bar – 20bar – 180bar – 350bar) – Manual stop

o This series of tests is performed 4 times

Note: filling time is quick (around 3 min), but

depressurization time is very long:

→ 1h45 + time to prepare cylinder for the

next filling (de-freezing)

Tests performed

Remark:

The tests performed in this test

campaign are more exhaustive than the

ones required by OIML R139, but also

more severe…

Specificities of HRS tested

Remark:

The CFM is located in the container, far from the dispenser

Test results

Measured accuracies

Discussions

• Influence of distance between CFM and dispenser

Advantages: stable working conditions of the CFM (low

variation of pressure and temperature)

Disadvantages: far from the transfer point (errors induced due

to the CFM location)

Discussions

• Influence of distance between CFM and dispenser

o Situation at beginning of a fuelingMass of H2 (pressure P1):

not counted but given to the customer

→ Depends on end pressure of previous filling

(independent of the customer)

Discussions

• Influence of distance between CFM and dispenser

o Situation at end of a fuelingMass of H2 (pressure P2):

counted but not in the customer tank

→ Depends on end pressure given by SAE J2601

protocol (automatic stop) OR manual stop decided

by the customer OR abnormal stop (fueling error)

Vented quantity: counted, but not

in the customer tank

Discussions

• Influence of distance between CFM and dispensero If P1 ~ P2: the customer pays exactly the quantity delivered in his tank ● Full fillings 200-700 bar

o Initial mass of H2 is replaced by the same quantity at end of fueling ● MMQ (1kg) 450-700 bar

m_delivered ~ m_invoiced

o If P1 > P2: the customer get more hydrogen than the quantity invoiced ● Partial fillings 20-350 bar

o Initial mass of H2 is replaced by a lower quantity at end of fueling ▲ MMQ (1kg) 20-180 bar

m_delivered > m_invoiced (negative error)

o If P1 < P2: the customer get less hydrogen than the quantity invoiced ● Partial fillings 350-700 bar

o Initial mass of H2 is replaced by a higher quantity at end of fueling ★ MMQ (1kg) 180-350 bar

m_delivered < m_invoiced (positive error) MMQ (1kg) 350-580 bar

Discussions

Measured accuracies

Outline

1. Introduction

2. Testing device to determine accuracy of meters and dispensers

3. Test campaign of hydrogen filling stations in operation

4. Preliminary conclusions and recommendations

Conclusions

• Good reliability of the testing device in real conditions

• Influence of the measuring system configuration (distance between the CFM and

the nozzle):

o The greater the pressure difference in the pipe at the beginning and end of the refueling

process, the bigger the error

• Recommendations:

o Reduce as much as possible the volume between CFM and the nozzle

o Knowing the precise volumes, errors can be calculated and corrected

Next steps

• Conclusions to be completed with upcoming results

• Deep analysis of all measurements (fueling data,

environmental conditions etc.)

• Deliverable (D1) – «Good practice guide describing

calibration and validation of flow meters used at HRSs for

quantifying hydrogen dispensed into vehicles»

→ For further details, refer to https://www.metrohyve.eu

Thank you for your Attention!

Empa – Swiss Federal Laboratories for

Materials Science and Technology

@Empa_CH