issues associated with measuring nothing

Center for Diesel Research

Issues associated with measuring nothing or

almost nothing: Real-time Measurements of

Metallic Ash Emissions from Engines

David Kittelson, Udayan Patwardhan, Darrick Zarling,

David Gladis, and Winthrop Watts,


Department of Mechanical Engineering

University of Minnesota

Cambridge Particle Meeting

Engineering Laboratory

Cambridge, England

24 May 2013



Measuring nothing

• The EU has set a number based emission standards for light and heavy duty Diesel vehicles

– The standards are based on “solid” particles larger than 23 nm

– Light-duty, Euro 5b, September 2011 • The standard is 6 x 1011 particles/km

• The mass emission standard is 4.5 mg/km, but the number standard corresponds to about 0.15 to 0.7 mg/km, depending on DGN – a much tighter standard!

– Heavy-duty, Euro VI, January 2013 • The standards are 6 x 1011 and 8 x 1011 particles/kWh on the WHTC and the WHSC,

respectively

• The mass emission standard is 10 mg/kWh, but the number standard corresponds to about 0.2 to 0.9 mg/kWh, depending on DGN – again a much tighter standard!

• The US so far plans to limit measurements to mass – Current US heavy-duty standard is 13 mg/kWh

– New US/CARB light-duty standards are 1.8 and 0.6 mg/km for 2017 and 2025 (maybe 2022), respectively. These correspond to roughly 8 and 3 mg/km

• It is very challenging to accurately measure filter mass at 13 mg/kWh. The new US/CARB standards represent an even greater challenge.

– Stoichiometric burn SI engines have about 13% water – limiting lowest dilution factor

– Light-duty cycle uses separate filters for 3 phases so a total mass of perhaps 30 mg is distributed on 3 filters each having 5+ mg artifact

– We hope the CRC E99 project figures all of this out

• Unfortunately the US hates number measurements


Real time ash measurements

Outline

• Introduction

– Why do we care about ash?

– How do they form

• Metals in lube oil – typically 0.5% metal, Ca, Zn, Mg,..

• Wear metals

– Structure and size

– Oil consumption pathways

• Method

• Initial engine results

• Calibration experiments

• New issues

• Conclusions


Acknowledgements

• We would like to thank BP and Corning for their

support of this work.

• The work was also partially supported by internal

funding from the U of M


Background work

• Kim, J. (2005). High Temperature Oxidation Method for Real-Time Measurement of Metallic Ash in Diesel Exhaust, Plan B Paper in Partial Fulfillment of the Degree of Master of Science, University of Minnesota.

• Filice, M.,, W. F. Watts and D. B. Kittelson 2007. Near Real-Time Ash Measurement: A Preliminary Study. Extended Abstract, Poster prepared for Seminar on Industrial Emissions and Immissions: New Problems Caused By Ultrafine Particulate. 11th International Trade Fair of Material & Energy Recovery and Sustainable Development, November 7-10, 2007, Rimini, Italy.

• Apple, James, David Gladis, Winthrop Watts, and David Kittelson, 2009. “Measuring Diesel Ash Emissions and Estimating Lube Oil Consumption Using a High Temperature Oxidation Method,” SAE Int. J. Fuels Lubr. 2(1): 850-859, 2009, also SAE paper number 2009-01-1843.

• Gladis, David Daniel, A Real-time Method for Making Engine Exhaust Ash Measurements, University of Minnesota, M.S. Thesis, September 2010


Importance of ash emissions

• Diesel engines - build-up and plugging of DPF

– Increased pressure drop - eventually

– Reduction of useful filter life, increased cleaning frequency

• Gasoline engines

– Deposition in 3-way catalyst leads to poisoning

– Same issues as diesel if GPF used

– Solid nanoparticle emissions if GPF not used, especially with metallic additives

• Relationship to engine lube oil consumption mechanisms

Ash distribution in exhaust filter channels

(Heibel and Bhargava, 2007)

3-way catalyst poisoning by ash deposits

(Franz, et al., 2005)


Particle formation history – 2 s in the life of

an engine exhaust aerosol

Kittelson, D. B., W. F. Watts, and J. P. Johnson 2006. “On-road and Laboratory Evaluation of Combustion

Aerosols Part 1: Summary of Diesel Engine Results,” Journal of Aerosol Science 37, 913–930.

Carbon formation/oxidation

t = 2 ms, p = 150 atm.,

T = 2500 K

Ash Condensation

t = 10 ms, p = 20 atm.,

T = 1500 K

Exit Tailpipe

t = 0.5 s, p = 1 atm.,

T = 600 K

Sulfate/SOF

Nucleation and Growth

t = 0.6 s, p = 1 atm.,

D = 10, T = 330 KFresh Aerosol over

Roadway–Inhalation/Aging

t = 2 s, p = 1 atm.,

D = 1000 T = 300 K

Increasing

Time

Formation

Atmospheric Aging

Exposure

This is where most of

the volatile nanoparticles emitted by

engines usually form.

There is potential to form

solid nanoparticles here if the ratio of

ash to carbon is high.

Particles formed by

Diesel combustion carry

a strong bipolar charge

Carbon formation/oxidation

t = 2 ms, p = 150 atm.,

T = 2500 K

Ash Condensation

t = 10 ms, p = 20 atm.,

T = 1500 K

Exit Tailpipe

t = 0.5 s, p = 1 atm.,

T = 600 K

Sulfate/SOF

Nucleation and Growth

t = 0.6 s, p = 1 atm.,

D = 10, T = 330 KFresh Aerosol over

Roadway–Inhalation/Aging

t = 2 s, p = 1 atm.,

D = 1000 T = 300 K

Increasing

Time

Formation

Atmospheric Aging

Exposure

This is where most of

the volatile nanoparticles emitted by

engines usually form.







Particles formed by

Diesel combustion carry

a strong bipolar charge


Engine ash emissions

Sappok and Wong, 2007

• Non-combustible fraction of diesel aerosol

• Derived from metallic lube oil additives and

engine wear metals

• Metallic particles tend to ‘decorate’

carbonaceous exhaust particles

• But form separate particles at sufficiently

high metal to soot ratios Jung, et al., 2005

Jung and Kittelson, 2005


Catalytic stripper measurements - nuclei mode usually

volatile but shows nonvolatile (ash) core at light load

4.5 LTier 4/Interim IIIB offroad diesel engine

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.0E+08

1.0E+09

1 10 100 1000Dp, nm

dN

/dlo

gD

p,

pa

rt/

cm

3

1400 RPM 240 Nm No CS

CS corrected

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.0E+08

1.0E+09

1 10 100 1000Dp, nm

dN

/dlo

gD

p,

pa

rt/

cm

3

900 RPM 25 Nm No CS

CS corrected

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.0E+08

1.0E+09

1 10 100 1000Dp, nm

dN

/dlo

gD

p,

pa

rt/

cm

3

2400 RPM 35 Nm No CS

CS corrected

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.0E+08

1.0E+09

1 10 100 1000Dp, nm

dN

/dlo

gD

p,

pa

rt/

cm

3

2400 RPM 175 Nm No CSCS corrected


Typical engine exhaust particle size distribution by

mass, number and surface area

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

1 10 100 1,000 10,000

Diameter (nm)

Norm

ali

zed

Con

cen

trati

on

(1

/Cto

tal)

dC

/dlo

gD

p

Number Surface Mass

Fine Particles

Dp < 2.5 µm

Ultrafine Particles

Dp < 100 nm

Nanoparticles

Dp < 50 nm

Nuclei Mode - Usually

forms from volatile

precursors as exhaust

dilutes and cools

Accumulation Mode - Usually

consists of carbonaceous

agglomerates and adsorbed material

Coarse Mode - Usually

consists of reentrained

accumulation mode particles,

crankcase fumes

PM10

Dp < 10 µmIn some cases this

mode may consist of

very small particles

below the range of

conventional

instruments, Dp < 10

nm

2

pDNS 6/3

pDNm

Most of the ash usually

found in decorated

particles in these 2 modes


Outline

• Introduction




• Wear metals



• Method



• New issues

• Conclusions

Center for Diesel ResearchGladis, 2010

Diesel exhaust or

other metallic ash

containing aerosol

Oxidize soot and

hydrocarbons within high

temperature tube furnace

Stable metal oxides and other

refractory metal compounds

are formed or survive high

temperature tube furnace

Cooled particles measured using

real/near-real time particle

instruments

High temperature oxidation method (HTOM)

overview


Outline

• Introduction




• Wear metals



• Method



• New issues

• Conclusions


Tube Oven

(1 LPM)

CAI Analyzer

Raw NO

Horiba NO Analyzer

Dilute NO

Engine

Exhaust

Vent

Ejector pump

diluter with critical

orifice

Supply Air

Oven Temperature

Logger

Thermocouple

Wires

SMPS

SMPS

Other

instruments,

EAD, EEPS

Engine exhaust apparatus

Gladis, 2010


Engine exhaust measurements: volume weighted size

distributions

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1 10 100 1000

Dp [nm]

dV

/dlo

gD

p [

μm

3/c

m3]

2009/11/02 - Ash

0.5 μm3/cm3

2009/11/10 - Ash

1.3 μm3/cm3

2009/11/12 - Ash

1.2 μm3/cm3

Total exhaust - upstream oven

1.9 L VW TDI engine; 1400 RPM/40 N-m; ULSD fuel

Gladis, 2010


Transient ash emissions

0

20

40

60

80

100

120

140

14:50 14:53 14:55 14:58 15:01 15:04 15:07

Time (HH:MM)

Par

ticl

e d

iam

eter

co

nce

ntr

atio

n (

mm

/cm

3)

0

10

20

30

40

50

60

70

80

90

Lo

ad (

N-m

)

Load

Ash

Gladis, 2010


Outline

• Introduction




• Wear metals



• Method



• New issues

• Conclusions


Lube oil spray apparatus

Supply Air

Catalytic Stripper Tube Oven

Atomizer

Activated CarbonVent

Vent

Manifold

2-Stage Ejector Dilution

SMPSSample flow controlled by SMPS

sample flow, 1 lpm *Sample Location Manually Switched

Ash Sample

Point*

Total Sample

Point*

AtomizerAtomizer

Vent

Manifold

Gladis, 2010


Lube oil spray results: evaporation and oxidation of

specially blended lube oils

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1 10 100 1000

Dp [nm]

dV

/dlo

gD

p [

μm

3/c

m3]

Typical Atomized Lube Oil

3.6E4 μm3/cm

3

Ca,P,S - 100A

2.6E2 μm3/cm

3

Zn,P,S - 101A

3.7E-1 μm3/cm

3

Ca,S - 102A

2.3E2 μm3/cm

3B,Mg - 103A

2.7E1 μm3/cm

3

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0 200 400 600 800 1000 1200

Maximum oven temperature [°C]

Par

ticl

e volu

me

frac

tion r

emai

nin

g

-

100A - Ca,P,S

101A - Zn,P,S

102A - Ca,S

103A - B,Mg,S

Gladis, 2010


Lube oil spray results: composition of specially

blended lube oils and ash survival fraction

Base stock

104A 101A 100A 103A 102A

B <5 <5 <5 285 <5

Ca <2 <2 3946 <2 3724

Mg <2 <2 8 ~500 <2

P 2 976 1052 <10 13

S 55 1998 802 57 8804

Zn <5 1008 <5 <5 <5

Blend # Element Compound

Concentration

[ppm] Expected Measured Measured/Expected

100A Ca CaCO3 3946 2.9E-03 7.3E-03 2.51

101A Zn ZnSO4 1008 5.9E-04 9.6E-06 0.02

102A Ca CaSO4 3724 3.4E-03 7.2E-03 2.10

103A Mg MgCO3 500 5.3E-04 7.8E-04 1.48

Metallic Volume Fraction

Oil composition, ppm, mass

Ash compound survival fraction

What happened to the zinc compounds?

Why is survival fraction so high for Ca and Mg?

Gladis, 2010


Outline

• Introduction




• Wear metals



• Method



• New issues

• Conclusions


New setup for transient ash measurements

Engine Dyno

Dilution Tunnel

Exhaust

Intake

MicroSoot

FTIR

Oven

EEPS

1100 °C, 1 lpm

LFE

HEPA

8 lpm

Gas Analyzer

PC

Dilution Air


Transient ash measurements during speed

ramps at heavy and light loads

0

5

10

15

20

25

30

35

40

45

50

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Elapsed time (s)

MS

ma

ss

(m

g/m

3),

EE

PS

V (m

m3/c

m3)

10

100

1000

10000

En

gin

e S

pe

ed

(R

PM

), E

xh

au

st

T (

C)

EEPS V smoothed EEPS V100 MicroSoot Engine Speed [RPM]

Exhaust Temp [C]


Real time black carbon and real time ash show

similar time response

• This is reasonable as we expect much of the ash to be

decorating soot particles (black carbon)

• But it could also mean that there is carbon

breakthrough, incomplete oxidation of particles

• Concentrations of ash downstream of oven are very

low so downstream ash measurements are

challenging

• Decided to borrow LII instrument to make these

measurements


Black carbon measured downstream of oven using

Artium LII300 during temperature ramp

0.001

0.01

0.1

1

10

12:30:00 13:00:00 13:30:00 14:00:00 14:30:00

Time of Day

LII

Ma

ss C

on

c, m

g/m

3

0

200

400

600

800

1000

1200

To

rqu

e, N

-m, O

ven

Tem

p, C

LII Mass Conc (mg/m³) Torque x5 [N-m] Oven Temp [C]

Room Air

Carbon disappears at 1100 SS but

a pulse appears during load spike


Raising the oven temperature to 1150 C eliminates

nearly all of the carbon breakthrough

0

125

250

375

500

12:30 12:45 13:00 13:15 13:30 13:45 14:00

Time of Day

Torq

ue

(N

-m)

0.001

0.01

0.1

1

10

LII M

ass

Co

nc

(mg/

m3)

Engine Torque [Nm]

Mass Concentration (mg/m³) LII US

LII US


Ongoing issues

• Need additional metal survival calibration, ICPMS

• What is happening to the zinc?

• Carbon breakthrough, interference

– Appears to be solved using 1150 C

– Likely associated with larger particles with insufficient time to fully oxidize

– Raise oven temperature

• Material limitations

• Ash volatilization and losses

– Remove coarse PM upstream of oven

• How much ash is carried by these particles?

• May be especially important on transients


Outline

• Introduction




• Wear metals



• Method



• New issues

• Conclusions


Conclusions

• We have developed a method that allows us to

measure exhaust ash emissions from engines in near

real time.

• Results suggest significant ash emission during

engine transients, both up and down in load and speed

• Concerns

– Lack of response to zinc

– Carbon breakthrough


Questions


References

• Heibel A, Bhargava R. Advanced Diesel particulate filter design for lifetime pressure drop solution in light duty applications. Fuels and Emissions Conference. 2007.

• Hill S, Sytsma S. A systems approach to oil consumption. SAE International Congress and Exposition. 1991.

• Kittelson D, Watts W, Johnson J. On-road and laboratory evaluation of combustion aerosols-Part1: Summary of diesel engine results. J Aerosol Sci. 2006;37(8):913-930.

• Kittelson D. Engines and nanoparticles: A review. J Aerosol Sci. 1998;29(5):575-588.

• Sappok A, Wong V. Detailed chemical and physical characterization of ash species in Diesel exhaust entering aftertreatment systems. SAE World Congress. 2007.


Lube oil consumption pathways

• Piston rings

– Atomization

– Ring collapse

• Leaky valve seals

• Crank case

ventilation and

exhaust gas

recirculation

(EGR)

Diagram of lube oil pathways on a typical engine

(modified from Hill and Systasma, 1991)


Typical engine result, VW TDI, light load cruise,

stable ash residue at 1100 – 1150 C

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

500 600 700 800 900 1000 1100 1200

Oven Temperature [C]

Ash

Vo

lum

e F

racti

on

Engine Out - Test 1 Engine Out - Test 2

issues associated with measuring nothing

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