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

Materials Science&Technology

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

CHAMBER TEST FACILITIESCHAMBER TEST FACILITIES

Dr. Martin Weilenmann

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

2Materials Science &Technology

Basic questionBasic question

What means system emissions of HWhat means system emissions of H22 vehicles? 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



Second questionSecond question

How to measure them?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



Subsequent questionsSubsequent questions

How to reach satisfactory accuracy?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?



Test cellTest cell

overall sketchoverall sketch



Test cellTest cell

Mass balance – exterior ventilationMass balance – exterior ventilation

Mass balance

Test cell with controlled overpressure only one inflow Measure total volume flow and H2 concentration (+

p,T)

2

2 2

2

2 2 2

* *

, ,

* * *

, _ , ,

HH in H out

HH vent in H car H out

mm m

tm

m m mt

2 2 2

* *

, _ , _, ,H vent in air vent inH in H inm c V



Test cellTest cell

Mass balance – exterior / Interior ventilationMass 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!



Test cellTest cell

Mass balance – Interior ventilationMass balance – Interior ventilation

Test with blowing a Helium balloon at time = 0 some 10 – 30 s

Helium concentration

0

5

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100 120 140

time (s)

He

[pp

m]

measured 1

exponential fit

measured 2

measured 3



Test cellTest cell

Mass balance – exterior / Interior ventilationMass 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)

2

22 2 2 2 2

* * *,

, , _ , _, _ ,H ch

H car air vent in air vent inH ch H vent in H H ch H

cV m c V c V

t



Test cellTest cell

Mass balance – validationMass balance – validation

Blowing a Helium balloon with known mass of Helium

Chamber volume known Ventilation known

0 500 1000 1500 2000 2500 30000

10

20

30

40

50Helium concentration in air exchange test

He

[ppm

]

time [s]0 500 1000 1500 2000 2500 3000

-4

-2

0

2

4

log( He - Heambient

)

He

[ppm

]

time [s]



SensorsSensors

Analyser propertiesAnalyser 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



Data processingData processing

Discretize mass balance equationDiscretize 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

2 2

2 2 2

*, , , , 1

, _ ,, , , , , , 1 , _ ,2H ch k H ch k

air vent in kG car k G H ch k H ch k ch H vent in k

c cm c c V V T c




Discretize mass balance equation IIDiscretize 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

t1T+t1

2

*

,H carm t

?

T+t1t1

2

*

,H carm t

T+t1t1

2

*

,H carm t

T+t1t1

2

*

,H carm t

Most probable Extreme cases




Discretize mass balance equation IIIDiscretize mass balance equation III

Constantlyemitting source:

Early peak:

Late peak:

*

2 2*2 2

*

, , , , 1, , , _

1

VT

VH ch k H ch k

H car k H vent inVT

V

c c eTVm c

Ve

2 2*2 2 2

, , , _, , , _ , , 1

H ch k H vent inH car k H vent in H ch k

VT

V

c cm V c c

e

*

2 2 2 2 2, , , , , _ , _ , , 1

VT

VH car k H ch k H vent in H vent in H ch km V c c c c e



ResultsResults

Comparison of approachesComparison of approaches

Maximal theoretical error: -12 ... 14 %

0 2000 4000 6000 8000600

800

1000

1200

1400

1600

1800

2000Hydrogen concentration

Con

c (H

2) [p

pb]

time [s]0 2000 4000 6000 8000

-1

0

1

2

3

4

5

6x 10

-3 massflow Hydrogen form car

Mas

sflo

w H

2 [g/

min

]time [s]

simple

const. em.

early peak

late peak

0 2000 4000 6000 8000-0.05

0

0.05

0.1

0.15

0.2Cumulated hydrogen emissions

Mas

s H

2 [g]

time [s]

0 2000 4000 6000 8000-0.2

-0.1

0

0.1

0.2

0.3Max local error

erro

r m

assf

low

H2 [

-]

time [s]



ResultsResults

Integral valuesIntegral values

Emissions in the range of mg/min are detectable

0 2000 4000 6000 8000600

800

1000

1200

1400

1600

1800

2000Hydrogen concentration

Con

c (H

2) [p

pb]

time [s]0 2000 4000 6000 8000

-1

0

1

2

3

4

5

6x 10

-3 massflow Hydrogen form car

Mas

sflo

w H

2 [g/

min

]

time [s]

simple

const. em.

early peak

late peak

0 2000 4000 6000 8000-0.05

0

0.05

0.1

0.15

0.2Cumulated hydrogen emissions

Mas

s H

2 [g]

time [s]

0 2000 4000 6000 8000-0.2

-0.1

0

0.1

0.2

0.3Max local error

erro

r m

assf

low

H2 [

-]

time [s]



ConclusionsConclusions

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.



ThanksThanks

To all partners and funding agencies

To you!

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

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