DIESEL EGR COOLER FOULING Powertrain Strategies for the 21st - - PowerPoint PPT Presentation

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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?