MODEL-BASED DETERMINATION OF HYDROGEN SYSTEM EMISSIONS OF MOTOR VEHICLES USING CLIMATE-CHAMBER TEST FACILITIES

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MODEL-BASED DETERMINATION OF HYDROGEN SYSTEM
EMISSIONS OF MOTOR VEHICLES USING CLIMATE-CHAMBER
TEST FACILITIES

• Dr. Martin Weilenmann

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Basic questionWhat means system emissions of H2
vehicles?

• System emissions may occur
• While parking leakage
• At start up density check, de-aerate
• While running poisoning purge
• At shutdown system ventilation
• What quantitative amounts are evaporated??
  Safety? Efficiency

Chassis Dynamometer needed
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Second questionHow to measure them?

• Based on mass balance in a test cell
• In a closed test cell
• Difficult to realise
• In a ventilated test cell if
• All in- and out- flows are known (mass flow)
• Concentrations of all in and out flows are known

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Subsequent questionsHow to reach satisfactory
accuracy?

• What requirements to the test cell?
• Exterior ventilation
• Interior ventilation
• What requirements to the sensors/analysers?
• Accuracy
• Sampling rate
• Positions
• How to process data?

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Test celloverall sketch
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Test cellMass balance exterior ventilation

• Mass balance
• Test cell with controlled overpressure
• ? only one inflow
• Measure total volume flow and H2 concentration (
  p,T)

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Test cellMass balance exterior / Interior
ventilation

• As pressure remains constant Inflow outflow
• But, what about outflow concentration?
• ? Precondition interior ventilations so high
  that chamber shows a homogenous concentration
• Climate machine
• Vent for car
• Under floor!

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Test cellMass balance Interior ventilation

• Test with blowing a Helium balloon at time 0
• ? some 10 30 s

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Test cellMass balance exterior / Interior
ventilation

• If interior ventilation homogenizes
  concentrations within seconds
• and if exterior ventilation is significantly
  slower (air exchange rate of several minutes)
• ? chamber concentration is homogenous and equals
  outflow concentration(s)

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Test cellMass balance validation

• Blowing a Helium balloon with known mass of
  Helium
• Chamber volume known
• Ventilation known

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SensorsAnalyser properties

• Gas chromatograph for H2 (RGA3)
• ppb range
• 10 ppb detection limit
• 2 minutes sampling rate
• ? Mass balance in discrete form
• Ambient H2 concentration monitored before and
  after the test and considered as constant

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Data processingDiscretize mass balance equation

• Most simple assume time step T (here 2 min) to
  be small compared to system dynamics.
• Implicitly assume all concentration signals to be
  almost constant during one time step

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Data processingDiscretize mass balance equation
II

• More advanced solve mass balance equation for
  each time step correctly.
• ? Need to know (assume) the signal shape of the
  vehicles emissions

?
Tt1
t1
Tt1
t1
Tt1
t1
Tt1
t1
Extreme cases
Most probable
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Data processingDiscretize mass balance equation
III

• Constantlyemitting source
• Early peak
• Late peak

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ResultsComparison of approaches

• Maximal theoretical error -12 ... 14

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ResultsIntegral values

• Emissions in the range of mg/min are detectable

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Conclusions

• System emissions can be monitored with
• A standard chassis dynamometer in a standard
  climate test cell plus
• a H2 sensor in ppb-range
• If
• Internal ventilation is high (within seconds) and
• External ventilation is slower than sampling time
• Flows of mg/min are detectable.

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Thanks

• To all partners and funding agencies
• To you!