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Dr. Martin Weilenmann

MODEL-BASED DETERMINATION OF HYDROGEN SYSTEM EMISSIONS OF MOTOR VEHICLES USING CLIMATE-CHAMBER TEST FACILITIES. Dr. Martin Weilenmann. Basic question What means system emissions of H 2 vehicles?. System emissions may occur While parking: leakage At start up: density check, de-aerate

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Dr. Martin Weilenmann

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  1. MODEL-BASED DETERMINATION OF HYDROGEN SYSTEM EMISSIONS OF MOTOR VEHICLES USING CLIMATE-CHAMBER TEST FACILITIES Dr. Martin Weilenmann

  2. 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 M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  3. 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 M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  4. 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? M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  5. Test celloverall sketch M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  6. Test cellMass balance – exterior ventilation • Mass balance • Test cell with controlled overpressure •  only one inflow • Measure total volume flow and H2 concentration (+ p,T) M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  7. 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! M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  8. Test cellMass balance – Interior ventilation • Test with blowing a Helium balloon at time = 0 •  some 10 – 30 s M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  9. 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) M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  10. Test cellMass balance – validation • Blowing a Helium balloon with known mass of Helium • Chamber volume known • Ventilation known M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  11. 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 M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  12. 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 M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  13. 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 ? T+t1 t1 t1 t1 T+t1 T+t1 T+t1 t1 Extreme cases Most probable M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  14. Data processingDiscretize mass balance equation III • Constantlyemitting source: • Early peak: • Late peak: M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  15. ResultsComparison of approaches • Maximal theoretical error: -12 ... 14 % M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  16. ResultsIntegral values • Emissions in the range of mg/min are detectable M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  17. 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. M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

  18. Thanks To all partners and funding agencies To you! M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www.empa.ch/abt 137

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