1 July 25, 2012

DIESEL EGR COOLER FOULING

University of Michigan: John Hoard

Mehdi Abarham Ashwin Salvi

Ford Motor Company:

Dan Styles

Powertrain Strategies for the 21st Century: Designing Global Powertrains Wednesday, July 25, 2012

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• Modern diesels use cooled EGR – Reduced engine out NOx emissions – May reduce particulate emissions

• Cooled surfaces foul – Soot - thermophoresis – HC, water, acids – condensation

• Processes have been modeled – Abarham et.al. • Uncertainties remain

– Removal mechanisms – In-situ morphology – Thermal properties of layers

• So, we built a visualization rig – Describe rig and show example test

Background

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Deposit Characteristics

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Thermophoresis is the Dominant Mechanism

• Scaling analysis of deposition mechanisms for a selected common boundary condition

From Abarham PhD thesis

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Scaling Analysis of Acting Forces

• Scaling analysis of forces acting on an attached particle to wall

– Drag

– Lift

– Weight

– Van der Waals

– Updraft force

• Van der Waals is strong enough to keep the particles attached

• It seems unlikely that particles are re-entrained by drag force or turbulent bursts at common EGR flow rates

From Abarham PhD thesis

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Deposited soot mass gain model results vs. experimental measurements

3 hours exposure time

Effectiveness drop model results vs. experimental measurements

3 hours exposure time

• Better estimation on mass deposited by the axi-symmetric model

• Overall, closer estimation of heat transfer reduction by the axi-symmetric model

CFD Models-Experiments Comparisons

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Tube effectiveness comparison longer time exposure

Cooler effectiveness comparison long time exposure

Model Results for Longer Term Exposures

Exhaust Filtered Exhaust

• For longer term experiments a soot removal mechanism is required to achieve correlation

• However, carefully constructed experiments to quantify the removal experiment did not yield the expected results. Further work required….

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EGR Cooler Visualization Test Rig

John Hoard, Mehdi Abarham, Tejas Chafekar Dennis Assanis, Dan Styles, “A Visualization Test Setup for Investigation of Water-Deposit Interaction in a Surrogate Rectangular Cooler Exposed to Diesel Exhaust Flow “, SAE paper 2012-01-0364, April 2012

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Test Stand Photo

Exhaust In

Air In

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Imaging Ability

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Surface Image During Deposition

Initial clean After two hours

50X magnification – brightness and contrast adjusted Note large particles

Large Particles

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Particle Sampling

• Normal diesel nanoparticles follow flows – Not likely to impact inertially – Thus, easy to sample

• Large particles (tens of microns) – 100X diameter, 10,000X area, 1,000,000X mass! – Separate inertially – Ideally need isokinetic sample – We used simple sample – Likely to miss many particles

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Magnified Image

200x magnification, imaging area 1.72mm by 1.29 mm.

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Particle Number versus Threshold T = 0.26

T = 0.29

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Engine-Out Sample

Max = 90 particles

Multiple images processed and averaged

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Typical Published Particle Size Distribution

Harris, S.J., Maricq, M.M., “The Role of Fragmentation in Defining the Signature Size Distribution of Diesel Soot”, J. Aerosol Science 33: 935-942, 2002.

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Coolant 9°C, Start Air then Exhaust

Each second in the movie is 4 minutes in real time.

March 22 test

Actual size 6.88x5.16mm 50X magnification

Flow

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Conclusions • EGR Cooling fouling is a surprisingly rich research area • Soot deposits due to thermophoresis - ~90% of deposit mass • Heavy HC (C12+) condense • Acidic water condenses • Removal mechanism is required but not understood • Heat transfer properties of deposits in-situ not known • Visualization rig to investigate

– Large particles – Water condensation removal – Experiments continue

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Acknowledgments

• This work was done at the University of Michigan’s Walter E. Lay Automotive Laboratory under sponsorship of Ford Motor Company Research and Advanced Engineering.

• Thanks to Ashwin Salvi for help in running the engine and test cell.

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Questions?

Diesel EGR Cooler FoulingSlide Number 2Slide Number 3Thermophoresis is the Dominant MechanismScaling Analysis of Acting ForcesSlide Number 6Slide Number 7EGR Cooler Visualization Test RigTest Stand PhotoImaging Ability�Surface Image During DepositionParticle SamplingMagnified ImageParticle Number versus ThresholdEngine-Out SampleTypical Published Particle Size DistributionCoolant 9°C, Start Air then ExhaustConclusionsAcknowledgmentsQuestions?