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

M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, Basic question What means system emissions of H 2 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, Second question How 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, Subsequent questions How 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, Test cell overall sketch

M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, Test cell Mass balance – exterior ventilation Mass balance Test cell with controlled overpressure  only one inflow Measure total volume flow and H 2 concentration (+ p,T)

M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, Test cell Mass 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, Test cell Mass 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, Test cell Mass 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, Test cell Mass 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, Sensors Analyser properties Gas chromatograph for H 2 (RGA3) ppb range 10 ppb detection limit 2 minutes sampling rate  Mass balance in discrete form Ambient H 2 concentration monitored before and after the test and considered as constant

M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, Data processing Discretize 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, Data processing Discretize 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 t1t1 T+t 1 ? t1t1 t1t1 t1t1 Most probable Extreme cases

M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, Data processing Discretize mass balance equation III Constantly emitting source: Early peak: Late peak:

M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, Results Comparison of approaches Maximal theoretical error: %

M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, Results Integral values Emissions in the range of mg/min are detectable

M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, Conclusions System emissions can be monitored with A standard chassis dynamometer in a standard climate test cell plus a H 2 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, Thanks To all partners and funding agencies To you!