PATHWAYS TO REDUCTION OF CO2 EMISSIONS FROM COMBUSTION
ENGINES
Alok Warey, Ph.D.
OUTLINE
Part 1: Technology Screening to meet 2025 CO2
Emissions Regulations (Co-PI) – On-going
Part 2: Fundamental Exhaust Gas Recirculation
(EGR) Cooler Fouling and Mitigation Study (PI) -
Completed
Quick overview of other projects
OUTLINE
Part 1: Technology Screening to meet 2025 CO2
Emissions Regulations (Co-PI) – On-going
Part 2: Fundamental Exhaust Gas Recirculation
(EGR) Cooler Fouling and Mitigation Study (PI) -
Completed
Quick overview of other projects
OBJECTIVE
Explore diesel engine technology combinations
that meet 2025 CO2 regulations consistent with
future emissions standards
Remain cost competitive
METHODOLOGY
CO2 emissions estimated for different diesel engine technologies over
the New European Driving Cycle (NEDC) and the Worldwide
Harmonized Light Vehicles Test Procedure (WLTP)
1-D Engine Model Vehicle Model
+
CO2 (g/km)
DIESEL ADVANTAGE OVER GASOLINE
Data from EPA show approximately
30% reduction in gallons/100 miles for
diesel (approx. 40% higher MPG)
Why is a diesel engine more efficient
that a conventional gasoline engine?
Common answers:
No throttling losses
Higher compression ratio
These are contributors, but the lean
combustion process of the diesel
engine is the main factor leading to
efficiency gain
Source: Light-Duty Automotive Technology,
Carbon Dioxide Emissions, and Fuel Economy
Trends: 1975 Through 2012, EPA, 2013
LEAN COMBUSTION
Increased dilution improves
indicated fuel conversion efficiency
by lowering temperatures and
increasing gamma (ratio of specific
heats).
Switching from exhaust dilution to
air dilution improves indicated fuel
conversion efficiency by increasing
gamma.
Increased dilution improves the
indicated efficiency by lowering
temperatures and decreasing heat
losses.
Source: Foster, Combustion Engines Efficiency
Colloquium, DOE 2010
Compression Ratio (CR)
ηig
LOW HEAT REJECTION
In-cylinder heat losses in modern diesel engines constitute a
significant part of thermodynamics losses.
Engine efficiency can be increased by retaining a greater
amount of combustion energy for conversion to mechanical
work.
Sensitivity studies show that, provided heat losses could be
minimized, there is potential for significant fuel consumption
improvement.
Several pathways to achieve low heat rejection.
BASELINE DIESEL vs LEAN LOW HEAT REJECTION (LLHR) ENGINE
FUEL ENERGY BREAKDOWN
Combined pumping and friction torques are comparable
Boosting system for lean combustion adds more pumping torque
Due to leaner combustion and higher effective expansion ratio the LLHR engine is more efficient
Centroid of heat release closer to TDC for similar peak cylinder pressure and cylinder temperatures
Lower energy in the exhaust
Brake
Exhaust
Friction Pumping
Heat Transfer
166 Nm/35 kW 75 Nm/15 kw 25 Nm/5 kW
Baseline LLHR Engine Baseline LLHR Engine Baseline LLHR Engine
CO2 EMISSIONS
0.90 0.92
0
0.2
0.4
0.6
0.8
1
1.2
BASELINE Diesel Lean Combustion + Low Heat Rejection [LLHR]
No
rmal
ize
d C
O2
Emis
sio
ns
NEDC WLTP
SUMMARY
Developing robust, cost-effective, lean combustion and low heat rejection
diesel engines will be challenging but the fuel economy benefits are
significant.
Challenges for engine optimization:
• Robust combustion control over all operating conditions
• Robust emissions control over all operating conditions
• Good fuel consumption under real world driving conditions
• Low combustion noise
• Exhaust temperature
This will require a coordinated effort between air handling, combustion,
aftertreatment and controls – a system optimization approach.
In order for this to work effectively it is important to focus research on
fundamental insights that have long-term value critical to achieving upper-
bound efficiency and lower-bound emissions.
OUTLINE
Part 1: Technology Screening to meet 2025 CO2
Emissions Regulations (Co-PI) – On-going
Part 2: Fundamental Exhaust Gas Recirculation
(EGR) Cooler Fouling and Mitigation Study (PI) -
Completed
Quick overview of other projects
EXHAUST GAS RECIRCULATION (EGR) COOLERS
EGR coolers are compact heat
exchangers used on all modern
diesel engines to cool exhaust
gasses that are re-circulated into the
combustion chamber.
Exhaust gas recirculation is used to
control NOx (oxides of nitrogen)
emissions that result from diesel
combustion.
Advanced diesel combustion
strategies to improve fuel economy
rely on cooled exhaust gas
recirculation (EGR).
EGR COOLER FOULING
Fouling of exhaust gas re-circulation (EGR)
coolers can result in significant deterioration of
the cooler effectiveness and increased
pressure drop across the cooler.
EGR cooler fouling can adversely affect the
combustion process, engine durability and
emissions.
Complicated flow physics with multiple soot
particle deposition and removal mechanisms.
Hydrocarbon and water condensation in
addition to soot deposition.
Goal of this research was to develop a
fundamental understanding of EGR cooler
fouling mechanisms and demonstrate novel
concepts to mitigate fouling and regenerate
fouled EGR coolers. Source: SAE 2010-01-1211
DIESEL EXHAUST PARTICLE EMISSIONS
Source: David Kittelson, University of Minnesota
EXPERIMENTAL SETUP
Intake Flow
Exhaust Flow
Exhaust Gas Analyzers
W/Heated Lines
DMS500
Switching Valves
Temperature / Pressure
EGR Valve Intake Throttle Valve
Turbocharger
EGR Bypass Valve
Compressor
CO2Analyzer
(EGR Flow)
Flow Meter
Clean Air (EGR Flowrate )
EGR Cooler
Heated/ Dilution Line
Temperature / Pressure
Engine Test Stand
at GM R&D
Single Rectangular Channel
EGR Cooler
Removable
Fouling Plates
EXPERIMENTAL SETUP
Lab Reactor – University of Stuttgart
Soot
Generator
Species Injection
Ports
Furnace
Emissions
Sampling
EGR
Cooler
EGR
Cooler
Bypass
Exhaust
Hood
THERMOPHORESIS
* Thermophoresis = Particle transport due to temperature difference (ΔT)
GM Proprietary
PSR Lab – Diesel Engine Systems Group
Thermophoresis* is the dominant mechanism for particle deposition in
EGR coolers.
Fouling will always occur as a result of the temperature difference,
which is necessary for heat exchanger operation.
1.E-13
1.E-12
1.E-11
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
0 100 200 300 400 500
Dep
osit
ion
velo
cit
ies (
m/s
)
Particle diameter (nm)
Thermophoresis
Diffusion
Turbulent Impaction
Gravitational Drift Left: ΔT ~ 0 °C Right: ΔT ~ 300°C
(Isothermal) (Thermophoresis)
0.0E+00
2.0E+07
4.0E+07
6.0E+07
8.0E+07
1.0E+08
1.2E+08
1.4E+08
1 10 100 1000
Pa
rtic
le C
on
ce
ntr
ati
on
[#
/cm
3]
Particle Diameter [nm]
25 °C 90 °C
EGR Cooler Outlet: 25 °C Coolant Temp.
90 °C Coolant Temp.
EGR Cooler Inlet
THERMOPHORESIS
0
5
10
15
20
25
30
35
40
45
50
0 20 40 60 80 100
So
ot
Dep
os
itio
n R
ate
[m
g/h
r]
EGR Cooler Coolant Temperature (°C)
Soot Deposition Rate
Accumulation Mode Particles
GM Proprietary
PSR Lab – Diesel Engine Systems Group
Particle measurements upstream and downstream of the EGR cooler
also show evidence of thermophoresis.
Soot deposition rate due to thermophoresis increases with decrease
in coolant temperature.
Bika, A.S., Warey, A., Long, D., Balestrino, S., and Szymkowicz, P.G., “Characterization of Soot Deposition and Particle Nucleation in Exhaust Gas Recirculation
Coolers”, Aerosol Science and Technology, 46(12): 1328-1336, 2012.
PARTICLE REMOVAL
GM Proprietary
PSR Lab – Diesel Engine Systems Group
Increasing wall shear stress due to gas velocity appears to be effective in
preventing dry soot accumulation on the cooler walls.
However, typical gas velocities through the EGR cooler are considerably
lower than 30 m/s for reasons of excessive pressure drop.
It is impractical to generate the high gas velocities necessary for deposit
removal through the cooler of a conventional diesel engine.
Abd-Elhady, M. S., Zornek, T., Malayeri, M. R., Balestrino, S., Szymkowicz, P. G., & Müller-Steinhagen, H., “Influence of Gas Velocity on Particulate Fouling of Exhaust
Gas Recirculation Coolers”, International Journal of Heat and Mass Transfer, 54(4): 838-846, 2011
30 m/s 70 m/s 120 m/s
EGR coolers typically
operate below 30 m/s
PARTICLE FORMATION
GM Proprietary
PSR Lab – Diesel Engine Systems Group
As the coolant temperature is decreased below 45 °C, nucleation mode
particle concentration begins to increase downstream of the cooler. This
trend is continued as the coolant temperature is decreased further.
Condensation of hydrocarbons occurs not only on the cooler walls but also in
the bulk gas.
0.0E+00
1.0E+07
2.0E+07
3.0E+07
4.0E+07
5.0E+07
6.0E+07
7.0E+07
8.0E+07
1 10 100 1000
Pa
rtic
le C
on
ce
ntr
ati
on
[#
/cm
3]
Diameter [nm]
Avg. Upstream 25C Downstream 30C Downstream 35C Downstream 40C Downstream 45C Downstream 50C Downstream Increasing
nucleation
mode with
decreasing
coolant temp.
EGR Cooler Outlet:
25 °C Coolant Temp.
30 °C Coolant Temp.
35 °C Coolant Temp.
40 °C Coolant Temp.
45 °C Coolant Temp.
50 °C Coolant Temp.
EGR Cooler Inlet
Bika, A.S., Warey, A., Long, D., Balestrino, S., and Szymkowicz, P.G., “Characterization of Soot Deposition and Particle Nucleation in Exhaust Gas Recirculation Coolers”, Aerosol Science
and Technology, 46(12): 1328-1336, 2012.
Warey, A., Bika, A.S., Long, D., Balestrino, S., and Szymkowicz, P.G., “Visualization and Analysis of Condensation in Exhaust Gas Recirculation Coolers”, SAE Paper 2013-01-0540.
EFFECT OF HYDROCARBON (HC) CONDENSATION
GM Proprietary
PSR Lab – Diesel Engine Systems Group
Significant changes in deposit morphology were observed due to
hydrocarbon condensation.
Condensed HC’s in the EGR cooler diffuse through the deposit layer and stay
near the cold wall. Cold wall inhibits evaporation of condensed HC’s.
Bika, A., Warey, A., Long, D., Balestrino, S., & Szymkowicz, P., “An Investigation of Diesel EGR Cooler Fouling And Effectiveness Recovery”, SAE 2013-01-0533
Tin = 215 °C FSN = 2.0
THC = 40 ppm C3
Flow: 200 SLPM
Exposure : 2 hours
Tcoolant: 25 C
Tin = 215 °C
FSN = 2.0
THC = 250 ppm C3
Flow: 200 SLPM
Exposure : 2 hours
Tcoolant: 25 C
Inlet Outlet
DEPOSIT ANALYSIS
GM Proprietary
PSR Lab – Diesel Engine Systems Group
Heavier hydrocarbons in diesel fuel tend to condense at coolant/wall
temperatures typically encountered in EGR coolers.
Deposit created at:
TGas = 215 °C Coolant = 25 °C
FSN = 2.0
THC = 250 ppm C3
(Post Injection)
Flow: 200 SLPM
Exposure : 2 hours
EFFECT OF WATER VAPOR CONDENSATION
GM Proprietary
PSR Lab – Diesel Engine Systems Group
Inlet Outlet
After Exposure to Water Vapor Condensation
Prior to Water Vapor Condensation
Tin = 215 °C FSN = 2.0
THC = 40 ppm C3
Flow = 200 SLPM
Exposure = 2 hours Coolant = 100 °C
Tin = 145 °C FSN = 0.3
THC = 65 ppm C3
Flow = 200 SLPM
Exposure = 30 min Coolant = 10 °C
Warey, A., Bika, A.S., Long, D., West, D., Balestrino, S., and Szymkowicz, P.G., “Influence of Water Vapor Condensation on Exhaust Gas Recirculation Cooler
Fouling”, International Journal of Heat and Mass Transfer, 65: 807-816, 2013.
EFFECT OF WATER VAPOR CONDENSATION
GM Proprietary
PSR Lab – Diesel Engine Systems Group Warey, A., Bika, A.S., Long, D., West, D., Balestrino, S., and Szymkowicz, P.G., “Influence of Water Vapor Condensation on Exhaust Gas Recirculation Cooler
Fouling”, International Journal of Heat and Mass Transfer, 65: 807-816, 2013.
0
100
200
300
400
500
600
700
800
900
0 10 20 30 40 50 60 70 80 90 100
Ma
ss
Co
nd
en
sa
tio
n F
lux
of
Wa
ter
Va
po
r (m
g/m
2s
)
Coolant Temperature (°C)
Water Vapor
Removal Mechanism
METAL PLATE METAL PLATE METAL PLATE METAL PLATE METAL PLATE
2.) H2O Vapor Diffuses
Through Soot Layer
3.) H2O Droplet Disrupts
Soot Adhesive Force 4.) Reduced Adhesive
Force Enables Removal
5.) Clean Cooler
Plate
1.) Soot Deposited
by Thermophoresis
Soot Particles/Layer are Hydrophobic
EFFECT OF WATER VAPOR CONDENSATION
GM Proprietary
PSR Lab – Diesel Engine Systems Group
Hydrophilic Deposit
METAL PLATE
METAL PLATE
Soot +HC
Droplet Forms/mixes on HC Surface
METAL PLATE
METAL PLATE
Dry Soot
Vapor Diffuses Through voids
METAL PLATE METAL PLATE
Clean Plate
HC’s fill voids
Possible Lacquer
Formation
Droplet Forms on
Metal Surface
Soot + HC yields Hydrophilic deposit
Condensation of water vapor
occurs on the surface of
hydrophilic deposits (not below)
and is unlikely to remove
deposits.
Hydrophobic Deposit
Warey, A., Bika, A.S., Long, D., West, D., Balestrino, S., and Szymkowicz, P.G., “Influence of Water Vapor Condensation on Exhaust Gas Recirculation Cooler
Fouling”, International Journal of Heat and Mass Transfer, 65: 807-816, 2013.
EFFECT OF OXIDATION CATALYST (OC)
GM Proprietary
PSR Lab – Diesel Engine Systems Group Warey, A., Bika, A.S., Vassallo, A., Balestrino, S., and Szymkowicz, P.G., “Combination of pre-EGR Cooler Oxidation Catalyst and Water Vapor
Condensation to Mitigate Fouling”, SAE International Journal of Engines, 7(1): 2014.
Specifications
Diameter mm 45
Length mm 120
Cell Density cpsi 200 LS
Volume L 0.19
Washcoat g/ft3 67.5 g/ft3 Pt / 22.5 g/ft3 Pd
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600 HC
Eff
icie
ncy
(%
) &
HC
Slip
(p
pm
C3)
HC Concentration (ppm C3)
HC Slip (ppm C3) HC Conversion Eff (%)
HC Conversion Efficiency
0.0E+00
2.0E+07
4.0E+07
6.0E+07
8.0E+07
1.0E+08
1.2E+08
1.4E+08
1.6E+08
1 10 100 1000
dN
/dlo
gDp
(#/
cm3)
Diameter (nm)
Active OC Upstream
Active OC Downstream
Inactive OC Upstream
Inactive OC Downstream
No significant loss of particles from active or inactive catalysts
Particle Size Distribution
Two Catalysts:
Active (Washcoat)
Inactive (NO Washcoat)
EGR Cooler OC
EFFECT OF OXIDATION CATALYST (OC)
GM Proprietary
PSR Lab – Diesel Engine Systems Group
0
20
40
60
80
100
120
140
Active OC Inactive OC
De
po
sit
Mas
s (m
g)
Engine Out - Soot + HC + H2O
After Vacuum Oven (2 hrs) - Mostly Soot
38%
49%
0
20
40
60
80
100
120
140
Active OC Inactive OC
De
po
sit
Mas
s (m
g)
Engine Out - Soot + HC + H2O After Vacuum Oven (2 hrs) - Mostly Soot
50 C Coolant Temperature 25 C Coolant Temperature
37%
53%
An oxidation catalyst upstream of the EGR cooler results in lower
accumulated deposit mass.
Warey, A., Bika, A.S., Vassallo, A., Balestrino, S., and Szymkowicz, P.G., “Combination of pre-EGR Cooler Oxidation Catalyst and Water Vapor
Condensation to Mitigate Fouling”, SAE International Journal of Engines, 7(1): 2014.
EFFECT OF OXIDATION CATALYST (OC) + WATER VAPOR CONDENSATION
GM Proprietary
PSR Lab – Diesel Engine Systems Group
Exposure to water vapor condensation in addition to the oxidation
catalyst results in significant removal of deposit mass.
50 C Coolant Temperature 25 C Coolant Temperature
34.8
68.4
14.5
29.5
0
20
40
60
80
100
120
140
Active OC Inactive OC
De
po
sit
Mas
s (m
g)
Engine Out - Soot + HC + H2O After Exp. to Water Cond. and Vac Oven - Residual Deposit
22.5
97.5
5.3
49.6
0
20
40
60
80
100
120
140
Active OC Inactive OC
De
po
sit
Mas
s (m
g)
Engine Out - Soot + HC + H2O After Exp. to Water Cond. and Vac Oven - Residual Deposit
Warey, A., Bika, A.S., Vassallo, A., Balestrino, S., and Szymkowicz, P.G., “Combination of pre-EGR Cooler Oxidation Catalyst and Water Vapor
Condensation to Mitigate Fouling”, SAE International Journal of Engines, 7(1): 2014.
EFFECT OF OXIDATION CATALYST (OC)
GM Proprietary
PSR Lab – Diesel Engine Systems Group
Saturation Ratio:
Pv (T) : Partial pressure of the condensing species
Psat (T) : Saturation pressure of the condensing species
Condensation typically occurs at SR > 1.0
)(
)(
TP
TPSR
sat
v
• EGR Coolant Temperature: 50 C
• Engine-out THC: 250 ppm C3
• 100% of the exhaust HC are
assumed to be n-hexadecane
(C16H34)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0% 20% 40% 60% 80% 100%
HC
Sat
ura
tio
n R
atio
in
EG
R C
oo
ler
[-]
Catalyst HC Conversion Efficiency (%)
NO Condensation
Condensation
Warey, A., Bika, A.S., Vassallo, A., Balestrino, S., and Szymkowicz, P.G., “Combination of pre-EGR Cooler Oxidation Catalyst and Water Vapor
Condensation to Mitigate Fouling”, SAE International Journal of Engines, 7(1): 2014.
1D FOULING MODEL
0.0E+00
2.0E+07
4.0E+07
6.0E+07
8.0E+07
1.0E+08
1.2E+08
1.4E+08
1.6E+08
1 10 100 1000
dN
/dlo
gD
p (
#/c
m3)
Diameter (nm)
Upstream Downstream: DMS500 Downstream: Model
Coolant Temperature: 50 °C
Flow direction
L
Do
x
r To(t) Co(t)
yHCo(t)
Tw (t)
Tm (x,t), Um (x,t), Cm (x,t)
Inlet (0m) Outlet (0.2m)
Warey, A., Balestrino, S., Szymkowicz, P.G., and Malayeri, M.R., “A One Dimensional Model for Particulate Deposition and Hydrocarbon Condensation in Exhaust
Gas Recirculation Coolers”, Aerosol Science and Technology, 46 (2):198–213, 2012.
1D FOULING MODEL
Warey, A., Balestrino, S., Szymkowicz, P.G., and Malayeri, M.R., “A One Dimensional Model for Particulate Deposition and Hydrocarbon Condensation in Exhaust
Gas Recirculation Coolers”, Aerosol Science and Technology, 46 (2):198–213, 2012.
EGR COOLER FOULING SUMMARY
Thermophoresis is the dominant mechanism for particle deposition in EGR
coolers.
Particulate fouling can be avoided if the gas velocity through the EGR cooler
is above a critical flow velocity.
Hydrocarbon condensation has the strongest influence on deposit
morphology changing it from a dry porous layer to sludge or lacquer like
deposit.
Significant removal of accumulated deposit mass was observed by using an
oxidation catalyst in combination with exposure to water vapor condensation.
Based on the findings in this study on-board “cleaning” or regeneration of the
EGR cooler by exposure to water vapor condensation does seem feasible.
OUTLINE
Part 1: Technology Screening to meet 2025 CO2
Emissions Regulations (Co-PI) – On-going
Part 2: Fundamental Exhaust Gas Recirculation
(EGR) Cooler Fouling and Mitigation Study (PI) -
Completed
Quick overview of other projects
OTHER PROJECTS
Fuel Effects on Low Temperature Premixed Compression Ignition
(PCI) Combustion in a Light-Duty Diesel Engine
Characterization of Particulate Matter (PM) Emissions from a 2007
Emissions Level Heavy-Duty Diesel Engine
Development of an Electronic Sensor for Engine Exhaust Particulate
Measurements – Doctoral Dissertation
Effects of In−Cylinder Wall Wetting on Size and Mass of Particulate
Matter Emissions in Direct Injection Spark Ignition Engines– Masters
Thesis
Guest Graduate – Argonne National Laboratory
o Used laser scattering to measure the time resolved size distribution and mass of
particulate matter (PM) emissions from a direct-injection gasoline engine
Thank You