MODELBASED DETERMINATION OF HYDROGEN SYSTEM EMISSIONS OF MOTOR

MODEL-BASED DETERMINATION OF HYDROGEN SYSTEM EMISSIONS OF MOTOR VEHICLES USING CLIMATECHAMBER TEST FACILITIES Dr. Martin Weilenmann Empa, ,

Basic question What means system emissions of H 2 vehicles? n System emissions may occur While parking: leakage n At start up: density check, de-aerate n While running: poisoning purge n At shutdown: system ventilation n n What quantitative amounts are evaporated? Safety sis er s Efficiency a et Ch om m a d Dyn eede n M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www. empa. ch/abt 137 2

Second question How to measure them? n Based on mass balance in a test cell n In a closed test cell n n Difficult to realise In a ventilated test cell if All in- and out- flows are known (mass flow) n Concentrations of all in and out flows are known n M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www. empa. ch/abt 137 3

Subsequent questions How to reach satisfactory accuracy? n What requirements to the test cell? Exterior ventilation n Interior ventilation n n What requirements to the sensors/analysers? Accuracy n Sampling rate n Positions n n How to process data? M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www. empa. ch/abt 137 4

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

Test cell Mass balance – exterior ventilation n Mass balance n Test cell with controlled overpressure only one inflow n Measure total volume flow and H 2 concentration (+ p, T) n M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www. empa. ch/abt 137 6

Test cell Mass balance – exterior / Interior ventilation As pressure remains constant: Inflow = outflow n But, what about outflow concentration? n Precondition: interior ventilations so high that chamber shows a homogenous concentration n Climate machine n Vent for car n Under floor! n M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www. empa. ch/abt 137 7

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

Test cell Mass balance – exterior / Interior ventilation If interior ventilation homogenizes concentrations within seconds n and if exterior ventilation is significantly slower n (air exchange rate of several minutes) n 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 9

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

Sensors Analyser properties Gas chromatograph for H 2 (RGA 3) n ppb range n 10 ppb detection limit n 2 minutes sampling rate n n Mass balance in discrete form n 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, www. empa. ch/abt 137 11

Data processing Discretize mass balance equation n Most simple: assume time step T (here 2 min) to be small compared to system dynamics. n 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 12

Data processing Discretize mass balance equation II n More advanced: solve mass balance equation for each time step correctly. n Need to know (assume) the signal shape of the vehicles emissions ? t 1 T+t 1 t 1 Most probable M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www. empa. ch/abt 137 T+t 1 Extreme cases 13

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

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

Results Integral values n 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 16

Conclusions n System emissions can be monitored with A standard chassis dynamometer in a standard climate test cell plus n a H 2 sensor in ppb-range n n If: Internal ventilation is high (within seconds) and n External ventilation is slower than sampling time n n Flows of mg/min are detectable. M. Weilenmann et al. Empa, Materials Science & Technology, Ueberlandstrasse 129, CH-8600 Duebendorf, www. empa. ch/abt 137 17

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 18