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Impacts of Advanced Combustion, Fuels and Aftertreatment Technologies on Diesel PM Emissions and Mobile Source Air Toxics:

A Ten-Year Retrospective

February 11, 2009

Chairman’s Air Pollution Seminar Series

California Air Resources Board

Sacramento, CA

John StoreyFuels, Engines, and Emissions

Research [email protected]

865-946-1232

2 Managed by UT-Battellefor the Department of Energy Presentation_name

Acknowledgements

• FEERC team: – Ron Graves (Director), Brian West, Jim Parks,

Sam Lewis, Bruce Bunting, Stuart Daw, Scott Sluder, Robert Wagner, Teresa Barone, Norberto Domingo and many others

• DOE support: Office of Vehicle Technologies– James Eberhardt, Gurpreet Singh, Ken Howden,

Kevin Stork, John Fairbanks

• EPA support: OTAQ– Dennis Johnson and Jim Blubaugh

• CARB – Alberto Ayala for inviting me


Diesel and light-duty diesel have specific challenges in public, regulatory acceptance

1979 Cadillac Diesel Sedan

1981 VW Rabbit Diesel Pickup

•1970’s-90’s tough for diesel

•GM diesel problems

•“Dump Dirty Diesel”Campaign

•CARB interest in diesel replacement with natural gas

•1998+ Government Response to Diesel Issues

•DEER conference

•Consent decree between OEMs, EPA

•Fuel sulfur rule

•EPA releases Diesel PM Toxicity


Who invented the diesel engine?

• Rudolf Diesel 1858-1913

• Much more efficient than steam engines of the time

• Original vision – to run on vegetable oils! – biodiesel isn’t such a

new idea

• Died mysteriously on ferry to England 1913


• Motivation, background of DOE and diesel

• Approach to lowering PM– Engine Hardware– Diesel Particulate Filters

• Current State-of-the-Art– Putting it all together into today’s vehicle– Retrofit PM control– Ultralow sulfur diesel and Biodiesel

• Future– Modeling Emissions Control Systems– Advanced combustion modes– Link to CO 2 emissions and climate change

The path forward…..


• Began as part of the Manhattan Project

• Nation’s largest multiprogram energy laboratory

• World’s first nuclear reactor and now leading producer of medical radioisotopes

• Nation’s largest unclassified scientific computing facility

• Nation’s largest science facility,the $1.4B Spallation Neutron Source

• Nation’s largest concentration of open source materials research

Oak Ridge National Laboratory

National TransportationResearch Center

High Temperature Materials Laboratory

Relevant Facilities


Transportation technology

Generation Storage and distribution Consumption

Transportation system analysis

Alternativefuels

Refining

Hydrogenproduction

Hydrogen storageand transport

Batteries &Power electronics

Internal combustion

Fuel cells

Hybrid Electric Vehicle


Fuels, Engines, & Emissions Research Center…. a comprehensive laboratory for internal combustion engine technology

• A DOE National User Facility in the NTRC

• Focusing on alternative fuels, advanced combustion, and emission control R&D

• Unique or extraordinary diagnostic and analytical tools for engine/emission control R&D

• R&D from bench-scale to vehicle– Chemical/analytical labs– 9 dynamometer stands: 25-600

hp– Chassis dynamometer– Full-pass engine controls

support research – Emissions analysis with high

resolution of time and species – Non-invasive optical and mass-

spec diagnostics – Modeling & simulation

Chassis dyno lab

Engine Cells

Chassis Dyno Lab

Analytical Labs

Offsite Projects


The DOE’s Transportation Agenda

• Energy Security, Energy Efficiency– Energy Data Book and http://www.fueleconomy.gov– Energy Independence and Security Act (EISA, 2007)

• 36 Billion gal/yr of renewable fuels (2022)• Limits to corn-based ethanol• Focus on cellulosic ethanol

• Office of Vehicle Technologies– Light-duty engine efficiency goal: 42% (2007) 45% (2010)– Heavy-duty efficiency goal: 50% (2006); 55% (2013)– Meet applicable emissions

• Office of Biomass Programs– Production via Cellulosic sources (biomass)

• Office of Hydrogen, Fuel cells, and Infrastructure Technologies– Automotive fuel cell emphasis


So why bring up the DOE vision?

• DOE saw diesel engines as meeting their goal of energy efficiency and security– Heavy-duty engine efficiency program– Light Truck Clean Diesel program

• Emissions control was the enabling technology for diesel

• 1998. DEER conference in Maine– Diesel Engine Emissions control Research– Organized by DOE (John Fairbanks)– < 100 attendees

• 2008 DEER conference in Dearborn– > 1300 attendees

http://www1.eere.energy.gov/vehiclesandfuels/resour ces/proceedings/index.html


DEER conferences are comprehensive

• Industry, academia, National Labs, non-profit– Special session for environmental advocacy

organizations

• Thrusts included health effects– First U.S. discussion of nanoparticles and health

• NOx and PM control sessions

• Now large focus on advanced combustion and energy efficiency


0

5

10

15

0 0.1 0.25 0.6 1.0

Evolution of Heavy Duty Diesel Engine Emission Control

Source – Pat Flynn, DEER 20001974 EPA (HC + NOx)

19881978 (HC + NOx)

1990

19911994

1998

1987 ModelsRetard TimingLower IMTShorten HRRLow Friction

1988 ModelsRetard TimingInc. Inj. PressHigher BoostHigher CR

1991 ModelsRetard TimingLow IMT/High IMPInc. Inj. Press.Variable Inj. Timing

Particulate [g/(HP-hr)]

NO

x [g

/(H

P-h

r)]

2004(2002)

CooledEGR


EPA’s emissions standards require substantial PM and NOx reductions for automotive diesels, too.

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FTP NOx Emissions (g/mi)

FTP

PM

Em

issi

ons

(g/m

i)

5

Bin 8

Tier 1, Through 2003

Tier 2 StandardsPhase-in 2004-2009

CurrentDiesel

Technology



• Approach to lowering PM– Engine Hardware– Diesel Particulate Filters





Diesel Engine

(compression ignition)

Gasoline Engine

(spark ignited)

hot flame region:

nitric oxides

spark plug

hot flame region:

nitric oxides +

smoke

fuel injector

How do diesels work, anyway?

Source:Caterpillar, 2003


Fuel injection - key subsystem of diesel

• Pump-line-nozzle (“ancient”)

• Unit injectors

• Common rail (state of art)

• Piezo (combined with

common rail emerging)

Source: Dieselnet.com

Injectortip


Injection pressure being increased to aid emission compliance

• Mechanical unit injector=1000 bar (1981)

• “HEUI” =up to 1450 bar

• Early generation common rail=1350 bar

• Latest piezo common rail=1800 bar

• The future (Bosch and others) 2000 bar = 29,000 psi

• WHY?– Tiny, tiny holes (<200 µm) needed to make a fine

spray, smaller particles– But , then pass ~ 1 gallon/hr through each hole!

One bar=14.5 psi

One Mpa=10 bar


Sequence of diesel fuel injection and beginning of combustion


NOx PM Trade-off curve has been moving

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0.16

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

NOx Emissions (g/mi)

PM

Em

issi

ons

(g/m

i)

5

Bin 8


CurrentDiesel

Technology



• Approach to lowering PM– Engine Hardware – Diesel Particulate Filters


• Future– Modeling Emissions Control Systems – Advanced combustion modes– Link to CO 2 emissions and climate change



Diesel PM control – Diesel Particulate Filters (DPF) and Diesel Oxidation Catalysts (DOC)

• DOCs use precious metal catalyst to burn off organi c fraction– Typical PM mass reduction is 30%– Used on heavy-duty pickup trucks in 90’s

• First DPF on a car – 1985 Mercedes 300 for Californi a market (not a success)– Need 700 °C to burn off soot with exhaust O 2

• Electrically-heated DPF’s in early 1990’s

• Early systems used DOC + DPF– NO → NO2, then the NO 2 oxidizes the soot

• Later DPFs use catalytic coating – Catalyst on DPF converts NO to NO 2, NO2 oxidizes soot


Diesel Particulate Filter uses ceramic honeycomb to trap PM

Trapped PM

Cell Plugs

Exhaust(PM, CO, HC)Enter

Ceramic HoneycombWall

Exhaust (CO 2, H2O)Out

23 Managed by UT-Battellefor the Department of Energy

DPF Assembly can replace muffler

Soot filtersubstrate

V-band +gasket

V-band +gasket

Inlet section withflow distributor

flow

Outlet sectionwith water trap

flow

V-band +gasket

Pre-catalyst


Early DPF field study in 2001 in NYC

Uncontrolled Regeneration

• Occurs when DPF accumulates excess soot

• Excess soot can be lit off during high load (hill, ex-way).

• If engine drops to idle during this burning, exhaust flow too low

• Internal DPF temperatures high enough to melt ceramic.

Source: B. Bunting, DEER 2001


Trap failure is very rapid, typically

TRAP FAILURE, BUS 6358, 2/26/01

0100200300400500600700800900

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TIME OF DAY

TE

MP

ER

AT

UR

E, d

eg.C

0

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4

6

8

10

trap in C

trap out C

press inhg


0100200300400500600700800900

1000

4:33

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4:43

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4:48

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4:53

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4:58

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5:48

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5:53

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TIME OF DAY

TE

MP

ER

AT

UR

E, d

eg.C

0

2


0100200300400500600700800900

1000

4:33

:10

4:38

:10

4:43

:10

4:48

:10

4:53

:10

4:58

:10

5:03

:10

5:08

:10

5:13

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5:18

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5:23

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5:28

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5:33

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5:43

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5:53

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TIME OF DAY

TE

MP

ER

AT

UR

E, d

eg.C

0

2

4

6

8

10

trap in C

trap out C

press inhg

Source: B. Bunting, DEER 2001


Hi Temp - Melting

Temp Gradients - Fracture

What we are trying to prevent What we are trying to prevent --Uncontrolled RegenerationUncontrolled Regeneration

Low load operation Excessive soot loading

High load operation ignites soot UNCONTROLLED REGENERATION


Configuration 1

Exhaust OutletSoot filter with catalyst

Dieselinjection

Configuration 2

Dieselinjection

Exhaust Outlet

Soot filter with catalystPre-cat

More of a slow burn than a flame thrower

Solution: active regeneration controls when the DPF is regenerated


………..Evolution into a system…

• Gasoline vehicle emissions control evolved into a system– Tailpipe approach with oxidation – early 70’s– Air pumps added, late 70’s– A/F ratio control + fuel injection – 80’s– Now completely tied together

• Diesel engine system– Better control of fuel injection– DPF with Active Regen– EGR for NOx control


Fuel – the missing link

• DPF development well on its way by 2001– But PM mass was higher with pump fuel

• Sulfur was the culprit – made sulfate aerosol in the exhaust pipe

• DOE had several large research efforts to address sulfur effects 1999-2002– DECSE (Diesel Emissions Control- Sulfur Effects)– DVECSE (Diesel Vehicle Emissions Control – SE)

• Result: EPA required 15 ppm S in 2006

• Analogous to tetraethyl lead removal – Driven by concerns for catalytic converter– Lower lead levels in people was a byproduct


The dirty diesel of the past is giving way to clean diesel technology

2008 Dodge Ram 2500 Pickup meets 2009 standards


Clean diesel cars available now

VW Jetta TDI

Mercedes E320 Bluetec


VW’s emissions controls a marvel of packaging

Source: Internationales Wiener Motorensymposium 2008


Almost 40% improvement in MPG

2009 Volkswagen Jetta 2009 Volkswagen Jetta

Diesel Vehicle Gasoline Vehicle

New EPA MPG

DIESEL

33 Combined 29

City 40 Hwy

REGULAR GASOLINE

24 Combined 20

City 29 Hwy

Annual Petroleum

Consumption

(1 barrel=42 gallons) 11.9 barrels 14.3 barrels

Source: fueleconomy.gov


Diesel fuel then and now…

• 1998: Low sulfur diesel rule in effect, largely for PM control. < 500 ppm S, ~450 ppm true– California: ~150 ppm S due to low aromatics

• 2006: Ultralow sulfur diesel for diesel emissions control < 15 ppm S, ~ 8 ppm true– How? The magic of hydrogen. Result is higher

cetane fuel - good for older engines

• Biodiesel: How does it affect PM emissions?– Generally lower PM mass, higher solubles– Alters behavior of DPF → ULSD ≠ B5 ≠ B20


Diesel PM retrofit

• Diesel oxidation catalysts (DOC) popular– Low cost, “bolt-on” solution– ~30% PM reduction

• Diesel Particulate Filters (DPF) offer best PM removal– Require maintenance, off-vehicle regeneration

• Crankcase emissions filtration– Crankcase breather significant source

• ORNL-EPA project examined both– Field-aged DPF from schoolbus– Crankcase PM mass and size


Extensive setup of 1999 Cummins B5.9 was necessary to carry out project

Engine

DPF

Transient Emissions

System


PM and HC go down with DPF

0.00200.00350.00660.00550

0.1

0.2

0.3

0.4

0.5

FTP1 FTP2 FTP3 BP-FTP1

BP-FTP2

DPF-FTP1

DPF-FTP2

CDPF-FTP1

CDPF-FTP2

Test Sequence

Em

issi

ons

(g/h

p.hr

)

PMHC


Time for FTP (sec)

0 300 600 900 1200

Num

ber

Con

cent

ratio

n (#

/cm

3 )

0

2000

4000

6000

8000

10000

12000 Hot FTP 1 (09/04/08)Hot FTP 1 (09/05/08)

Total Particle Number Concentration During FTP Cycles

Downstream of DPF

Outdoor Air Concentration


Unique sampler design imposes no vacuum or pressure on crankcase

• All of PM collected

• ∆p < 0.5” H 2O observed at inlet of tunnel

• PM as much as 18% of regulated limit

To Roots Blower + Flow Measure

PressureMeasurement

SMPS outlet

HEPA Filter

Twin 70mmFilter Holders


PM emissions from draft tube significant

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stea

dy-s

tate

2000

rpm

, 23

bar

1400

rpm

, 30

bar

1800

rpm

, 30

bar

805r

pm, 0

bar

Cra

nkca

se P

M (

g/hp

.hr)

0

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0.25

Cra

nkca

se P

M (

g/hr

)

Basew. Bpw. DPFSteady StateIdle

*


dp (nm)

100 101 102 103 104 105

dN/d

logd

p (#

/cm

3 )

0.0

5.0e+7

1.0e+8

1.5e+8

2.0e+8

2.5e+8

SMPSAPS

µg = 114 ± 2 nm Ctot = 2.9 x 107 #/cm3

Crankcase Emissions Number-Size Distribution

dp (nm)

101 102 103 104 105

dN/d

logd

p (#

/cm

3 )

0.0

5.0e+7

1.0e+8

1.5e+8

2.0e+8

2.5e+8

SMPSAPS

µg = 159 ± 2 nm Ctot = 1.4 x 108 #/cm3

Increased Backpressure

Engine Baseline

Backpressure 280 mbarat rated speed (1400 RPM)

Rated Torque1400 RPM, 300 ft.lbs

(similar to 100% A on 13 mode)


Findings from Retrofit DPF Study

• Field aged DPF (3+ years in service) as received evaluation– DPF very efficiently removing PM– Clean DPF: higher number concentrations until soot layer

builds

• Crankcase emissions – mostly oil droplets– PM mass emissions = 3 X DPF out emissions– PM size shows significantly larger particles

• Crankcase PM treatment complements DPF retrofit

• Model Year 2007 and beyond closes the crankcase

Presentation at 2009 CRC On-Road Emissions Workshop


Modeling used extensively to improve combustion efficiency, emissions

Addressing the fundamental losses of combustion flames

Increased use of computational tools


Catalyst Modeling takes off from 2000 on….

• Objective to improve ability to simulate advanced emissions controls

• CLEERS (cleers.org) has annual workshops and working groups for NOx and PM control

• Broad participation from industry, academia, labs

• Past presentations available on the web site– Created and maintained by ORNL

Cross-Cut L ean Exhaust E missions R eduction S imulations


Modeling Extended to Engines, Vehicles

•Modeling the growth of the soot layer in a DPF duri ng a drive cycle

•No active regeneration of the filter (DPF)

0

1

2

3

4

5

6

7

8

0 1372 2744 4116 5488 6860Time (s)

Soo

t Lay

er W

idth

(µµ µµm

)

0

2

4

6

8

10

12

14

16

Eng

ine-

Out

PM

(m

g/s)

Soot layer Width

Engine-out PM

Source: ORNL Systems Modeling, 2008


High Efficiency Clean Combustion (HECC)

• HECC includes– Homogeneous Charge Compression Ignition (HCCI)

– Premixed Charge Compression Ignition (PCCI)

– others

• Improve powertrain system efficiency by lowering performance requirements for post-combustion emissions controls.

Objectives of ORNL efforts

• Detailed emissions characterization for understandi ng combustion regimes and environmental impact.

– Hydrocarbon speciation (MSATs!)

– PM characterization


Exhaust Gas Recirculation (EGR) key to advanced combustion modes

• EGR on most diesel engines since 2002

• How does EGR work?– Lowers NOx by diluting charge (air) with exhaust ga s

– lowers peak combustion temperature

– Typically increases PM

• High levels of EGR result in lower NOx and PM


Exhaust

Air

Air HXN

Engine Coolant

DPF

HP

EG

R H

XN

Shaft Work

Turbo

Typical Exhaust Gas Recirculation (EGR)

scheme


Motivation – 1999 study with VW TDI engine

0

0.4

1.0

1.4

20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0

EGR %

NO

x, P

M g

/hp-

hr

PM

NOx

0

0.4

1.0

1.4

20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0

EGR %

NO

x, P

M g

/hp-

hr

PM

NOx


Diesel Engine

(compression ignition)

hot flame region:

nitric oxideshot flame region:nitric oxides + smoke

Gasoline Engine

(spark ignited)

HCCI Engine

(Homogeneous Charge

Compression Ignition)

Low temperature combustion

ultra low emissions !!

spark plugfuel injector

What is this High Efficiency Clean Combustion?

Source:Caterpillar, 2003


Images of Conventional and HCCISource: Caterpillar, DEER Conference, 2002

Conventional Diesel HCCI

PCCI = Pre-mixed charge compression ignition


Advanced combustion changes the NOx-PM trade-off curve

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0.14

0.16

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

FTP NOx Emissions (g/mi)

FTP

PM

Em

issi

ons

(g/m

i)

5

Bin 8


Tier 2 StandardsPhase-in 2004-2009

CurrentDiesel

Technology

With “advanced”combustion


0

5.0

10.0

15.0

500 1000 1500 2000 2500 3000 3500

Engine Speed (rpm)

BM

EP

(ba

r)

02

13

4

5

Steady state modes used with HECC to approximate Light-duty FTP cycle.

• BSFC equivalent to baseline operation.

• Emissions lower

0.0

0.5

1.0

NOx PMConventional

HECC

Estimated FTP Emissions Index(Normalized)

What about HCs and CO?


High EGR = high formaldehyde and acetaldehyde formation.

0

0.1

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0.5

0.6

0.7

0.8

0.9

22.2 34.9 40.2 44.3 46.3 48.8 54.0 56.0

EGR %

DN

PH

Mas

s C

once

ntra

tion

mg/

s

Formaldehyde Acetaldehyde Acrolein

Propionaldehyde Benzaldehyde


What are Mobile Source Air Toxics (MSATs)?

Mobile Source Air Toxics (MSATs)

Particulate Matter (PM)

Volatile Organics

Semivolatile Organics

MetalsDiesel PM

Polycyclic organic Matter (POM)

Formaldehyde

Acetaldehyde

1,3-Butadiene

Acrolein

Benzene

Toluene

Ethylbenzene

XylenePolycyclicAromatic

Hydrocarbons (PAHs)

Diesel Exhaust Organic Gases


Array of Analytical Techniques for MSATs

Catalyst

Dilution

Tunnel SMPSParticle Size Distribution

PM Filters

Total PMSOF/insolubleSOF speciation

EmporeSelective capture of semi-volatiles (C10-C18)

GC/MS speciation

DNPH

Selective capture of carbonyl species

HPLC, UV, ESI/MS separation/speciation

Canisters

Light HC species

Preconcentrator, GC/MS speciation

FTIR

C1-C4 species


DOC Oxidation of Formaldehyde Not Complete Until ~225ºC

• CO, HC, and formaldehyde oxidation efficiency as a function of catalyst temperature– CO oxidation enables higher

oxidation of HCs and formaldehyde

– Formaldehyde oxidation not complete until 225ºC

• Engine at 1500 rpm/ 1.0 bar during cool down of catalyst from previous higher load operation

0

10

20

30

40

50

60

70

80

90

100

125 150 175 200 225 250

Catalyst Temperature (C)

Con

vers

ion

COHCFormaldehyde

• Thermal management can enable DOC to be kept at tem perature where suitable CO/HC/Formaldehyde oxidation occurs, but…

– What is the efficiency penalty associated with main taining formaldehyde oxidation vs. CO/HC oxidation?


0

1

2

3

4

5

Formaldehyde Acetaldehyde

Em

issi

ons

Inde

x (g

/kg

fuel

)

1500 rpm, 2.6 bar0

1

2

3

4

5


Em

issi

ons

Inde

x (g

/kg

fuel

)

1500 rpm, 1.0 bar

Catalyst Temperature

119ºC

256ºC220ºC

Low catalyst temperature presents challenges for tailpipe aldehydes in PCCI mode

Tier 2, Bin 5 formaldehyderegulation 0.24 g/kg fuel

0

1

2

3

4

5


Em

issi

ons

Inde

x (g

/kg

fuel

)

2000 rpm, 2.0 bar

Conv., Engine OutPCCI, Engine OutPCCI, Catalyst Out


Particle size measurements

• Why measure particle size?– Nanoparticles linked to health effects

– Number of particles may be more important than mass

• Modern engines reduce PM size to reduce mass

• With DPFs, PM mass measurement difficult– European Union adopting number based regs

– CARB investigating number-based system as well

Engine out DPF out

64 Managed by UT-Battellefor the Department of Energy Presentation_namedp (nm)

1 10 100 1000

dN/d

logd

p (

#/cm

3 )

0

2e+7

4e+7

6e+7

8e+7Conv.: Engine OutPCCI: Engine Out

Number s are similar, but PCCI particles much smaller

PCCI PM smaller in size at low load and medium load

Number of particles > 100 nm decreases

dp (nm)

1 10 100 1000dN

/dlo

gdp

(#/

cm3 )

0

2e+7

4e+7

6e+7

8e+7Conv.: Engine OutPCCI: Engine Out

46 nm23 nm


What does all of this mean for greenhouse gas emissions?

• CO2 directly related to fuel efficiency– Engines have been getting more efficient, but..

– …PM emissions controls reduce efficiency• Backpressure, fuel needed for active regeneration

• N2O and CH4 emissions can be a concern– Catalyst systems can make N 2O

– Advanced combustion can make more CH 4

• 2010 regulations could be paradigm shift– Urea-SCR NOx removal efficiency could allow

higher fuel efficiency


Summary

• Engines, PM control have advanced considerably in ten years

• DPFs close to 99% efficient

• Retrofits showing good durability

• Packaging of systems remains a challenge

• DOE continues to push technology for better efficiency


Resources

• DEER presentations– http://www1.eere.energy.gov/vehiclesandfuels/res

ources/proceedings/index.html

• CLEERS– http://cleers.org

• Society of Automotive Engineers– www.sae.org

• Health Effects Institute– 2008 Mobile Source Air Toxics report at

www.healtheffects.org


Extra slides


X-Ray Imaging Scouting Study Approach: Measurements with commercial 3D x-ray

X

D

• MDXi400 by 3D-XRAY, Ltd onsite NTRC March-May 08

• Rotating platform & X-ray fan beam give 3D profiles

• Used for defect detection in catalytic monolith production

• Examined cracks, thermal damage, washcoat uniformity, soot & ash DPF deposition

• Responds to CLEERS poll interest in DPF monitoring


Significant Results (6): Confirmed measurement of DPF soot distribution in-can

0

0.5

1

1.5

2

0 0.2 0.4 0.6 0.8

X-ray response (a.u.)S

oot L

oadi

ng (

g)

• 6-in OD uncoated DPF (in can)• Loaded for 5 hours on

Mercedes 1.7-L engine with ULSD fuel

• Quantitative detection of axial soot loading variations thru can wall

Linear calibration curve


Significant Results (7): Also confirmed ability to image details of DPF thermal damage

• 150mm DPF in can

• Thermal damage (by OEM) induced near exit

• Expect to be highly useful for model/OBD validation

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