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Page 1 DEER 2011
Emissions Controls Technologies, Part 1
EGR Cooler Fouling – Visualization of Deposition and Removal Mechanisms
17th Directions in Engine-Efficiency and Emissions Research Conference Detroit, MI – October, 2011
Dan Styles, Eric Curtis, Nitia Ramesh Ford Motor Company – Powertrain Research and Advanced Engineering
John Hoard, Dennis Assanis, Mehdi Abarham University of Michigan
Scott Sluder, John Storey, Michael Lance Oakridge National Laboratory
Page 2 DEER 2011
Benefits and Challenges of Cooled EGR
• Benefits Enables more EGR flow Cooler intake charge temp Reduces engine out NOx
by reduced peak in-cylinder temps
NOx
PM Increasing EGR
Rate
Increasing EGR Cooling
• Challenges Future emissions standards
Higher EGR rates More cooling
More HC’s More likely HC condensation Potentially more PM/SOF HC/PM deposition in cooler
or FOULING
After 200 hr. Fouling Test
Page 3 DEER 2011
What is EGR Cooler Fouling?
• Deposition of Exhaust Constituents on EGR Cooler Walls Decreases heat transfer effectiveness and increases flow restrictiveness
Page 4 DEER 2011
Previous DEER Conferences
• Focus on physics of deposition Key factors: gas/coolant temperatures,
gas velocities, exhaust constituents
Controlled experiments at Oakridge National Laboratory (ORNL) using fouling “sampler” for good test repeatability and separation of variables.
Key findings: High gas flow velocities reduce trapping efficiency
Lower coolant temperatures lead to higher HC condensation more deposit mass accumulated
Higher gas temperatures lead to thermophoretic soot deposition greater loss of heat transfer “effectiveness”
Importance of deposit layer composition thermal conductivity
Benefits of an EGR catalyst for EGR Cooler Fouling Reduction
EGR Cooler Fouling Sampler
Diesel Exhaust
Page 5 DEER 2011
Previous DEER Conferences, continued
• Model of EGR Cooler Fouling Analytical, 1D and 2D models
Variable layer thickness
Variable layer thermal conductivity
Thermophoresis and condensation
More details tomorrow at 8:30!
Good correlation for first 3 hours
Longer term experiments model over-predicts effectiveness loss
Missing physics Removal mechanism
Sticking coefficient < 100%
Thermal conductivity change
Page 6 DEER 2011
The Impact of EGR Cooler Fouling
EGR Cooler Performance at Steady State Freeway Cruise(Shutdown/Restart Every 5 Hours)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 5 10 15 20 25 30 35 40 45 50Runtime (hrs)
EG
R-c
oole
r effe
ctiv
enes
s (-)
0
EGR Flow Rate
Intake Charge Temperature
NOx
EGR Cooler 1st Pass
EGR Cooler 2nd Pass
• Note stabilization and “recoveries” of effectiveness loss
Tgas,in – Tgas,out Tgas,in – Tcoolant
ε = = qactual qmax theoretical
Page 7 DEER 2011
EGR Cooler Recoveries • Shutdown/restart recoveries correlated to coolant
temperature. Water condensation? EGR Cooler Performance Test and Steady State Freeway Cruise
(Shutdown/Restart every 5 hours)
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
0 10 20 30 40 50 60 70 80 90 100 110 120
EGR-cooler runtime (hrs)
EG
R C
oole
r Effe
ctiv
enes
s
0
EG
R R
ate,
Inta
ke C
harg
e Te
mpe
ratu
re
EffectivenessIntake temperatureEGR Rate
warm-up with EGREGR starting @ 30°C coolant
warm-up with EGREGR starting @ 20°C coolant
warm-up with EGREGR starting @ 40°C coolant
Page 8 DEER 2011
Steady State Stabilization
• Longer term “steady state” experiments require removal mechanism match slope of effectiveness degradation.
• Predicted soot gain mass gain is 45.1 mg (no removal) vs. 13.2 mg (removal)
• What is the mechanism?
Fin type EGR cooler.
Gas inlet temperature = 330ºC
Gas inlet pressure = 190 kPa
Coolant temperature = 90ºC
FSN ≈ 1
Page 9 DEER 2011
Deposit Removal Mechanisms • Flow force removal
Drag Lift Turbulent burst
• Deposit layer loosening
Water condensate “washing” Mechanical vibrations Flow/pressure pulsations Thermal stress cracking Particle scrubbing Flaking Spallation
• Deposit layer change
Layer wetting Layer collapse
• Reactions
Evaporation Chemical reactions
Deposit Erosion at Leading Surface/Peak of Wavy Fin
(courtesy Michael Lance – ORNL)
Page 10 DEER 2011
Deposit Removal Scaling Exercise
• Removal mechanisms allowing for analytical formulation are insignificant relative to “sticking” mechanism
2*2 )(8 νρν pD duF =
3*2 )(076.0 νρν udF pL =
3)(6 pgpw dgF ρρπ
−=
2012ZdAF pHv =
– Drag – Lift – Weight – Vander Waals – Updraft force 3*2 )(1.10 νρν udF pC =
Page 11 DEER 2011
Deposit Visualization Rig
• Test rig developed at University of Michigan allowing for direct optical access to deposition process Can observe fouling/removal in real time Diesel engine producing exhaust gas Confidential method to keep “window” clean Digital video microscope Cooled surface produces deposition Hot air stabilization
Heated Glass Window
Page 12 DEER 2011
Initial Tests
• Rig creates deposits similar to EGR coolers
• Deposit build up in fairly short time frame
• Several initial observations • Gouges or flakes observed
Before and after deposition in a 2 hour test 150x Magnification
Deposit thickness after 3 hours
Page 13 DEER 2011
Particle Bombardment
• Larger particles measured traveling in engine exhaust 10-80 μm sized particles
• Appear to be associated with “flakes” or “grooves” removed from deposit layer
• Further results planned for upcoming conference
50X
200X 50X
Page 14 DEER 2011
Confirmation of Water Condensate Removal
• 18 hour deposition test at 80ºC coolant • Coolant temperatures switched to 40ºC • Evidence of water condensate fracturing deposit layer
Page 15 DEER 2011
Water Condensate Removal
• Coolant temperature lowered to 20ºC with hot air stabilization • Switch to exhaust gas resulted in immediate condensation • Condensate appears to form below deposit layer and carry away
Page 16 DEER 2011
Other Removal Mechanisms
• Other removal mechanisms observed • Currently under investigation • 50X magnification
May 20, 2011
Specimen inlet
Specimen – Middle Section
Specimen outlet
Flow Direction
Page 17 DEER 2011
Key Conclusions • Cooled EGR is an increasingly important NOx reduction
technology for current and future diesel engines. • Higher EGR flow rates and cooling levels required by future
emissions regulations exacerbate fouling, or the deposition of soot and HC exhaust constituents, degrading EGR cooler performance.
• An EGR cooler fouling model is developed and correlated to shorter term controlled EGR cooler fouling experiments.
• Longer term EGR cooler fouling experiments appear to require a “removal mechanism” to achieve correlation.
• A deposit visualization rig has been developed and is running experiments to observe these suspected removal mechanisms in real time.
• Water condensation and large particle bombardment appear to be important removal mechanisms. Other removal mechanisms are under investigation.
Page 18 DEER 2011
Thanks for Your Attention
• Questions?
