Thermal and Flow Modeling & Validation of an Exhaust Gas Particulate Matter Sensor

Transcription

1 Thermal and Flow Modeling & Validation of an Exhaust Gas Particulate Matter Sensor A. Lourdhusamy, B. Henderson, J. Steppan, V. Wang, J. Fitzpatrick, K. Allmendinger EmiSense Technologies, LLC Salt Lake City, Utah M. Hall and T. Diller, University of Texas Austin, Texas ASME 2014 Verification and Validation Symposium 1

2 Outline Brief introduction of Particulate Matter (PM) or Soot sensor CFD modeling of Alpha version PM sensors Validation of CFD model of Alpha version PM sensor through experiments FEA modeling, CFD CHT modeling of Beta version PM Sensors Validation of CFD CHT & FEA models of PM Beta sensors through experiments Temperature validation Flow validation Summary Acknowledgements ASME 2014 Verification and Validation Symposium 2

3 Introduction PMTrac Alpha PM Sensor Design Insulator Metal coating Collection Electrode HV-Electrode Version A0 - Lab version Based on electrostatic principle. Two Electrodes: One at 1000V DC -HV Electrode Another is at 0-V- Ground or Collection Electrode Current is measured at collection electrode as the soot laden exhaust gas passes through the sensor. In situ(installed just like an O2 sensor) Electronic Sensor, Tracks soot concentration in real time of automobile exhaust gas. PM Emission limits & OBD sensor for DPF failure ASME 2014 Verification and Validation Symposium 3

4 A0 Issues with the Sensor Housing/Flow Design 1. Orientation sensitive-electrodes position varied 2. Sensor performance non-repeatable - Non uniform flow through sensor 3. Direct high velocity impingement of soot onto electrodes 4. Distinctive soot patterns on the electrodes & reduction of effective electrode area 5. Quick fouling of insulator area As the gas flow had no direction/uncontrolled EGV ASME 2014 Verification and Validation Symposium 4

5 Alpha Sensor Development version A0 to version A1 Baffle tube added Venturi tip added A1 A0 Direct the flow towards active Electrode zone ASME 2014 Verification and Validation Symposium 5

6 Verification CFD Model of A1 version Pressure A portion of 4 dia tail pipe with the sensor in position was included in the model. Isothermal; Only fluid domain modeled and no solids. Simple K-E turbulence model. No particles physics Mass Flow; EGT Fluid domain modeled in CFD Meshed 3D Model ASME 2014 Verification and Validation Symposium 6

7 Velocity Profile Comparison A0 with A1 A0 A1 Flow across electrode vs Flow along the electrode Vectors in random direction vs Well defined inlet & outlet ASME 2014 Verification and Validation Symposium 7

8 Velocity in the Middle of Active Electrodes at EGV 14 m/s EGV A0 Impinging velocity on electrode: 22 m/s EGV A1 No direct impingement; velocity on electrode < 4 m/s ASME 2014 Verification and Validation Symposium 8

9 Velocity Vectors near Insulator Velocity vectors towards insulators and caused fouling Frequent regeneration A0 version Velocity vectors towards outlet and away from insulator Baffle+ Venturi design A1 version ASME 2014 Verification and Validation Symposium 9

10 Velocity at Outlet more Uniform with A1 ve +ve +ve ve Non uniform flow & recirculation Non repeatable sensor performance Velocity on bottom holes A0 Unidirectional flow towards exit made sensor behavior more predictable & repeatable Velocity on venturi exit A1 ASME 2014 Verification and Validation Symposium 10

11 Summary of Improvements seen from A0 to A1 Qualitative Validation 1. Orientation sensitivity significantly reduced 2. Repeatable sensor performance 3. High velocity impingement of soot onto electrode eliminated 4. No soot patterns visible on the electrodes 5. Less fouling of insulator as the gas flow is now directed to the outlet due to suction at venturi tip A0 Flow regime shifted from highly Turbulent to Laminar flow along the electrodes A1 ASME 2014 Verification and Validation Symposium 11

12 Experimental Validation at Room Temperature : UT-Austin Metering rotameter One of the electrodes replaced with hot wire Anemometer Air flows from rotameter and forced through inlet holes, baffle tube holes past hotwire anemometer through venturi to the exit Flow through calibration fixture ASME 2014 Verification and Validation Symposium 12

13 Experimental Validation at Room Temperature : UT-Austin Hot wire anemometer equipped sensor housing installed & tested in a wind tunnel Free stream velocity measured with Pitot tube Calibration curve at room T Hot wire anemometer output correlated with volumetric flow ASME 2014 Verification and Validation Symposium 13

14 Experimental Validation at Room Temperature : UT-Austin Sensor 041: Measured stand off distance above venturi exit to Anemometer is Sensor 028: Measured stand off distance above venturi exit to anemometer is X Marks Mean velocity for 0.2 seconds Blue Dots: Peak to peak range. R^2 =0.994 Anemometer position critical ASME 2014 Verification and Validation Symposium 14

15 CFD CHT Modeling & Validation during Beta Sensor Development Beta sensor with single electrode Optimized Inlet, Baffle & Venturi exit hole size & numbers - Gas entry perpendicular exhaust gas direction Thermally optimized to keep components at optimum Temperature Two models created to verify the conceptual designs 1. FEA model for solids only-abaqus - Thermal optimization studies. 2. CFD model- Conjugate Heat Transfer StarCCM+ ( Solids & Fluid domain included in the model and conduction, convection & radiation modes of heat transfer included) - First principles mathematical model of sensor operation requires accurate gas flow rate & gas temperature through sensor ASME 2014 Verification and Validation Symposium 15

16 CFD CHT Model of Beta Sensor B2 Design Verification Ambient T Inlet: Mass flow; EGT Outlet: Pressure Solids imported from Solidworks into CFD Fluid+ Solid domain CHT+ Thermal radiation ASME 2014 Verification and Validation Symposium 16

17 Conjugate Heat Transfer CFD Model with Gray Thermal Radiation Solids+ Fluid Meshed Velocity Temperature Velocity vectors ASME 2014 Verification and Validation Symposium 17

18 Temperature Validations by Thermocouple Instrumented Sensor B2 Thermocouple Instrumented Sensor B2 CFD CHT Model ASME 2014 Verification and Validation Symposium 18

19 Temperature & Flow validations at EmiSense Test Rig Blower 1. EGV & EGT Variation 2. Averaging Pitottube 3. Mass flow meter based on thermal anemometry Heater Dilution air Control panel Test section Diesel Engine ASME 2014 Verification and Validation Symposium 19

20 1 Grommet 2 Heater 3 Hex 4 Electrode space 5 Venturi tip Good agreement(+/ 5%) of components Temperatures over the range of EGV s & EGT s ASME 2014 Verification and Validation Symposium 20

21 Beta Sensor Flow Validations using Hot Wire Anemometer Inlet flow from Mass flow controller Outlet Hot wire Anemometer fitted sensor Flow through calibration setup at Emisense ASME 2014 Verification and Validation Symposium 21

22 Anemometer Calibration: Emisense Forced flow through Sensor at Different T s Anemometer max operating T is 150 deg C ASME 2014 Verification and Validation Symposium 22

23 Sensor flow at 150 deg C EGT, Model vs. Measured 1 ST Sweep 2 nd Sweep Flow within +/ 10% for EGV <22 m/s Flow within +/ 16 % for EGV >22 m/s 2 nd Sweep ASME 2014 Verification and Validation Symposium 23

24 Possible reasons for variations from experiments to model at high EGV 1. Anemometer electronics non Temperature compensating version 2. Inaccuracy in measurement of exhaust gas velocity at pipe(hot wire vs. Avg Pitot tube) 3. Velocity vectors not ideally perpendicular to anemometer filament 4. V(k) variations at the location of anemometer (From model) with EGV 5. Flow through calibration setup has a more uniform velocity across the sensor cross section ASME 2014 Verification and Validation Symposium 24

25 Variations of Velocity at the Middle of Venturi Tip with EGV Velocity at Approximate location of Anemometer EGV EGV= 7 m/s, T= 200 C EGV= 30 m/s, T= 200 C (The location of Peak velocity Is shifted to the Right as EGV goes up) Velocity at Venturi Exit ASME 2014 Verification and Validation Symposium 25

26 Flow through Calibration Setup Uniform Velocity profile in electrode space More uniform velocity across Anemometer in calibration Setup as compared to real operating condition ASME 2014 Verification and Validation Symposium 26

27 Summary CFD Modeling & FEA modeling were instrumental in verifying/optimizing our conceptual housing design and subsequent first principles model development. Experimental testing helped validate the CFD model & sensor design. Thermal validation(experiments vs Model) were good Within +/ 5% of experiments. CFD model sensor volumetric flow predictions at room T are very close to experiments. CFD CHT model sensor volumetric flow predictions are within +/ 10% at low EGV s and +/ 16% at high EGV s for reasons explained above. ASME 2014 Verification and Validation Symposium 27

28 Acknowledgements Lee Sorensen for building instrumented PM sensors Mike Boettcher for calibration & testing at Emisense ASME 2014 Verification and Validation Symposium 28

29 Back up slides ASME 2014 Verification and Validation Symposium 29

30 CFD CHT vs FEA Model Temperature Validation EGV FEA model Solids only Heat transfer Model with assumed heat transfer coefficients EGT 500 deg C EGV 50 m/s & EGT 500 deg C CFD CHT Model EGV 90 m/s & EGT 500 deg C ASME 2014 Verification and Validation Symposium 30

31 1 Grommet 2 Heater 3 Hex 4 Electrode space 5 Venturi tip CFD model was slightly better as compared to FEA model ASME 2014 Verification and Validation Symposium 31

32 B2 Sensor Housing Flow & T Characteristics Being used in sensor first principles mathematical model ASME 2014 Verification and Validation Symposium 32