Simulator for Automotive Evaporative Emissions Restraint Systems

Transcription

1 Simulator for Automotive Evaporative Emissions Restraint Systems Presentation Dr.-Ing. Stefan Schlüter, Fraunhofer UMSICHT, Germany COMSOL Conference 2016 Munich

2 Introduction Automotive Evaporative Emissions Evaporative emissions from the fuel tanks of parked cars = 11,4 kg/year per car Vapor restraint systems = active carbon canisters, used in every car worldwide Parking car: fuel gases are adsorbed by the adsorptive system Driving car: fuel gases are desorped from the adsorber by fresh combustion air EU Goal 10% of all fossil fuels replaced by biofuels until 2020 Project Goals Research on adsorption of Bioethanol/Fuel blends on automotive active carbons Development of a simulation model for the adsorption/desorption process No. 2

3 Simulation Model Model development 2-d axisymmetric multicomponent adsorption model for COMSOL Multiphysics 5.2 Adsorption/desorption of gaseous fuel components on active carbon Gas components: Pentane (as fuel replacement), Ethanol, Water, Nitrogen Adsorption isothermes for specific active carbon types from experiments Adsorption and desorption process models COMSOL implementation 2-d axisymmetric geometry Equation based modeling Porous Media Models of COMSOL (Heat Transfer, Transport of Diluted Species) BDF Time Stepping, Fully Coupled, Jacobian update on every iteration No. 3

4 Model Equations I Darcy flow equation u dp KD P P G G laminar part of Ergun equation (Re < 1) Mass conservation equation T c K n1 P G ig, D G G G i G P t t i1 t G eff * 1 a Y Y M S i i P i i i 1 MN 1 MN 1 P M T M 2 2 with,, M M G G i i N G G G G 2 No. 4

5 Model Equations II Component conservation equation, gas phase c i eff D i, Gci ci P S 1 t G Component conservation equation, solid phase K Yi t Yi t a Y Y eff * i P i i linear driving force (LDF) adsorptive mass transfer Linear driving force coefficient gas-solid mass transfer 10 ( T ) 1 RT dy d (1 ) 1 ( ) 2 ( ) Bi * eff i, P S S S i GS, i P i with i, Bi * P d 5 P i P Pi TS di Pi TS adsorption isotherme No. 5

6 Model Equations III Energy equation, gas phase T P c T c T a T T t t Energy equation, solid phase G u G G P, G eff G G P, G G GS GS G S ads TS eff S (1 ) cp, S Yi M icp, i (1 ) S TS i t S TG Yi ads G S (1 ) hi cp, i dt Mi GSaGS TG TS i t T Energy equation, tube wall c T t T 0 W W W W W No. 6

7 Experimental Installation Break Through Experiments flue 2. adsorber temperature probes effluent weighting active carbon wall cooling nitrogen cryostate No. 7 adsorber gas preparation unit liquid adsorbents

8 Loading [mol/kg] Example: Pentane Adsorption Isotherme 9 8 Pentane on Active Carbon (1) C Exp 24 C Exp 24 C Exp Wdh. 35 C Exp 10 C 24 C 35 C 50 C 75 C 100 C 125 C 2 1 Data adaption with Langmuir-Freundlich 0 0, ,0001 0,001 0,01 0,1 1 relative Saturation = P i /P sat [1] No. 8

9 Simulation Runs Adsorption Experiments Adsorption of Pentane 100% on dry Active Carbon (1), 20 l/h N 2 Adsorption of Pentane/Ethanol 78%/22% (E22) on dry Active Carbon (1), 20 l/h N 2 Adsorption of Pentane/Ethanol 78%/22% (E22) on wetted Active Carbon (1), 20 l/h N 2 Desorption Experiments Desorption directly after adsorption cycle with Nitrogen at ca. 20 C from top Probes Temperature Probes T2-T7 at same positions as in experiment Simulation Time dependent simulation with experimental conditions No. 9

10 Temperature / Pentane-Loading in the Adsorber temperature Pentane loading No. 10

11 Temperature / Loadings / Gas Mole Fraction temperature Pentane loading Pentane mole fraction Ethanol loading No. 11

12 Model Valididation Pentane 100% on Active Carbon (1), 20 l/h N2 140 Adsorption Pentan 100% 20 l/h N2 130 Simulation 120 Temperatur [ C][ C] Temperature Kanal 2 (Exp.) Kanal 2 (Sim.) 90 Experiment Kanal 3 (Exp.) 80 Kanal 3 (Sim.) 70 Kanal 4 (Exp.) 60 Kanal 4 (Sim.) 50 Kanal 7 (Exp.) Kanal 7 (Sim.) Zeit [s] Time [s] No

13 Model Validation Pentane/Ethanol E22 on Active Carbon (1), 20 l/h N2 140 Adsorption: (EtOH+H2O) 22% + Pentan 78% 20 l/h N2 bis Durchbruch (2g) 130 Simulation 120 Temperature Temperatur [ C] [ C] 110 Kanal 2 (Exp.) 100 Kanal 2 (Sim.) 90 Kanal 3 (Exp.) 80 Experiment Kanal 3 (Sim.) 70 Kanal 4 (Exp.) 60 Kanal 4 (Sim.) 50 Kanal 7 (Exp.) Kanal 7 (Sim.) Zeit [s] Time [s] No

14 Temperature [ C] Model Valididation Pentane/Ethanol E22 on wetted AC (1), 20 l/h N Mixture 78% Pentane / 22% Ethanol on wetted Active Carbon (1), 20 l/h N 2 90 Experiment Simulation T2_exp T3_exp T4_exp T5_exp T6_exp T7_exp T2_sim T3_sim T4_sim T5_sim T6_sim T7_sim Time [s] No. 14

15 Adsorption / Desorption Cycle 3 Adsorption 1 Adsorption 3 Adsorption 2 No. 15

16 Conclusions I Adsorption runs Good reproduction of temperature probe signals in simulation: time of probe temperature increase rate of probe temperature increase maximum probe temperature radial temperature distribution Adsorption / desorption cycle runs Pentane loading decrease from cycle to cycle (as seen in experiments) Reason: unsufficient desorption, expecially in the lower part of the adsorber No. 16

17 Conclusions II Simulator Good reproduction of the physical system Small timesteps (1e-6 s to 5 s) necessary due to steep adsorption front Robust numerical time stepping with fussy solver parametrization Simulation times in the range of minutes for minutes process time Use of the simulator in further project work planned No. 17

18 Many thanks for your attention! Thanks to public funding: German Federal Ministry of Economics and Technology (BMWi, IGF N) German Federal Ministry of Education and Reserarch (BMBF, FKZ ) No. 18