Massachusetts Institute of TechnologySloan Automotive LaboratoryCambridge, MA

Characteristics and Effects of Lubricant Additive Chemistry and Exhaust Conditions on Diesel Particulate Filter Service Life and

Vehicle Fuel Economy

A Consortium to Optimize Lubricant and Diesel Engines for Robust Emission Aftertreatment Systems

August 5, 2009

Alexander Sappok, Victor W. Wong, Maureen Murage

0.0

0.5

1.0

1.5

2.0

- 5,000 10,000 15,000 20,000 25,000 30,000

Space Velocity [1/hr]

Pre

ssur

e D

rop

[kPa

]

Ash Impacts Diesel Particulate Filter Performance

Ash Sources

Lubricant additives (Zn, Ca, Mg, S, P)

Engine wear, corrosion, trace metals in fuels

Source: K. Aravelli

Courtesy: E. Senzer

Fundamental Understanding of Ash Properties Lacking

Ash Mitigation

CJ-4 oil specification -

limits sulfated ash to 1.0% maximum

Novel DPF designs and substrates –

asymmetric, membranes, and others

Reduced engine oil consumption

5 µm5 µm

Most of Material Trapped in DPF is Ash

0%

20%

40%

60%

80%

100%

0 50 100 150 200 2500510152025303540

Tota

l Ash

Lev

el [g

/l]

Ash

Fra

ctio

n [%

]

VWallVChannel

Service Interval [miles x 1,000]

Ash @ 42 g/l:

75% ash in end-plug (vol.)

-27%

DPF channel area

-40%

DPF channel length

No Ash Ash

After only 33,000 miles over 50% of material trapped in DPF is ash.

Cummins ISB 300

Variable geometry turbocharger

Cooled EGR

Common rail fuel injection

Fully electronically controlled

Gaseous Emissions

CAI 300 HFID –

Hydrocarbons

CAI 400 HCLD –

NO/NOx

CAI 602P NDIR –

CO/CO2/O2

API 100 E –

SO2

Particulate Emissions

Sampling and comparison to burner

Experimental Apparatus –

DPF Performance Testing

Cummins ISB 300 with DPF

Cummins ISB used for DPF performance evaluation before and after

ash loading tests on accelerated test rig.

Accurately Simulate Key Oil Consumption Mechanisms•

Each parameter independently variable•

Precise control of quantity and characteristics of ash generated

Accelerated Ash Loading System

System Specifications•

Exhaust heat exchangers –

counter flow •

Centrifugal blower –

backpressure control•

D5.66”

x 6”

DPF

Key Test Parameters

Lubricant Composition

All oils except pure base oil formulated to 1% sulfated ash

DPF Specifications

Substrate –

Cordierite D5.66”

x 6”

200/12, catalyzed

Test Fuel -

ULSD (Metals below ICP MDL ~1.0 –

0.05 ppm)

B Ca Fe Mg P Zn S Mo[ppm] [ppm] [ppm] [ppm] [ppm] [ppm] [ppm] [ppm]

CJ-4 586 1388 2 355 985 1226 3200* 77Base Oil 1 <1 <1 <1 8 <1 60 <1Base Oil + Ca 3 2928 1 5 2 <1 609 <1Base Oil + ZDDP 1 <1 <1 <1 2530 2612 6901 <1

ASTM D5185

Lubricant

DPF Ash Loading

Ash loading to max 42 g/l (equivalent on-road exposure ~ 240k miles)

Periodic regeneration cycle

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75Time [hr]

Pre

ssur

e D

rop

[kP

a]

0

150

300

450

600

750

Tem

pera

ture

[C]

Typical Accelerated Ash Loading Cycle

Loading Cycle

•

55 cycles

•

1 hour loading @ 250 °C inlet

•

15 min. regen @ 600–620 °C inlet

•

Constant exhaust flow rate

•

Exhaust temp. varied via heat exchangers

Temperature Cycles

∆P Cycles

DPF Post-Mortem Analysis

1

2

3

4 5

A B C D

1.5” 1.5” 1.5” 1.5”

DPF Sectioned

(4) Axial sections: 1.5”

long

(5) Radial samples: ~140 –

180 cells

(20) samples per DPF

Sample Measurements

Ash weight

Ash layer thickness and volume

Ash composition XRD, SEM-EDX

Individual Additive Effects on Pressure Drop (Ash)

Lubricant additive chemistry affects ash properties and pressure

drop

Ca-based ash shows much larger effect on pressure drop than Zn ash

Flow Bench @ 25 °C, Space Velocity: 20,000 hr-1

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 5 10 15 20 25 30 35 40 45

Pre

ssur

e D

rop

[kP

a]ρPack

= 0.25 g/cm3

ε

= 91%

ρPack

= 0.30 g/cm3

ε

= 91%

ρPack

= 0.19 g/cm3

ε

= 95%

Equivalent Miles*

Equivalent Hours* 2,840 4,260 5,670110 K 160 K 220 K

CJ-4Ca

Zn

* Assumes: 15 g/hr avg. oil consumption, avg. speed of 40 mph, and full size DPF of 12 L volume

Cumulative Ash Load [g/l]

Ash First Accumulates Along DPF Channel Walls

0.0

0.3

0.5

0.8

1.0

1.3

1.5

0 25 50 75 100 125 150

Cha

nnel

Wid

th [m

m]

57 mm 133 mm

12.5 g/l Ash

Center Center - 18 mm Center -36 mm Center Center - 18 mm Center -36 mm

0.0

0.3

0.5

0.8

1.0

1.3

1.5

0 25 50 75 100 125 150Axial Distance [mm]

57 mm 133 mm

42 g/l Ash

Plug

60% of ash layer thickness formed from initial 30% of ash deposit

Ash preferentially deposited in end-plug during later stages of ash build-up

0.0

0.2

0.4

0.6

0.8

0 25 50 75 100 125 150Axial Distance [mm]

Ash Layer Thickness Profiles Similar for All Lubricants

Ash

Lay

er T

hick

ness

[mm

]C

hann

el O

pen

Are

a [%

]

Plug

Ash Layer Thickness

Ca and Zn ash show slightly thicker ash layer vs. CJ-4 oil despite lower ash levels

Ash deposits on walls before forming ash plug

Channel Open Area

Channel area reduced 27% to 40%

Despite similar deposit profiles, Zn ash showed much lower pressure drop

Ash properties (K) affected by lube chemistry0%

20%

40%

60%

80%

100%

0 25 50 75 100 125 150Axial Distance [mm]

Ca 29 g/l Zn 28 g/l CJ-4 42 g/l

Additive Chemistry Affects Ash Packing Density

Significant difference in packing density for ash along wall vs.

plug

Ash in end-plug less densely packed than ash along channel wall for CJ-4 oil

Variation in packing density less pronounced for Ca and Zn ash

Pac

king

Den

sity

[g/c

m3 ] 0.30

0.17

0.250.22

0.19 0.17

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

57 133Axial Distance [mm]

CJ-4 42 g/l Ca 29 g/l Zn 28 g/l

Zn2

Mg(PO4

)2, CaSO4

Zn2

(P2

O7

), Zn3

(PO4

)2

CaSO4

0

3

6

9

0 1 2 3 4 5 6 7 8

Ash loaded DPFs exhibit non-linear pressure drop response to PM loading

Ash decreases pressure sensitivity to low PM loads <0.5 g/l

Ash increases pressure sensitivity to PM loads >3.0 g/l

Flow Bench @ 25 °C, Space Velocity: 20,000 hr-1

Individual Additive Effects on Pressure Drop (Ash+Soot)

Zn (28 g/l)

Ca (29 g/l)CJ-4 (33 g/l)

No Ash

Cumulative PM Load [g/l]

Pre

ssur

e D

rop

[kP

a]

Soot Deep Bed Eliminated

X

0.18

1.49

3.20

0.11

0.97

2.13

0.12

1.00

1.76

0.00.51.01.52.02.53.03.5

I II III

RP

S

CJ-4 (33 g/l) Ca (29 g/l) Zn (28 g/l)

Individual Additive Effects: Pressure Drop Sensitivity

Relative Pressure Sensitivity

(< 0.5 g/l PM) (0.5 –

3.0 g/l PM) (> 3.0 g/l PM)Pressure Drop Regime

Ca and Zn base oils show similar effects on pressure drop sensitivity, particularly for soot loads < 3.0 g/l

Fully-formulated CJ-4 oil shows largest effect on pressure drop sensitivity

RPS iCleaniAsh PM

PPMP

,,

Ash and Soot Effects on Fuel Economy (CJ-4)

FEP estimate assumes adiabatic expansion of ideal gas through turbo

Model inputs from experimental data

Soot + ash results in largest increase in FEP

0%

1%

2%

3%

4%

5%

6%

0 1 2 3 4 5 6

DPF Soot Load [g/l]

Fuel

Eco

nom

y P

enal

ty [%

]No Ash 12.5 g/l Ash 33 g/l Ash 42 g/l Ash

No Ash

12.5 g/l Ash

33 g/l Ash

42 g/l Ash

Ash effect on FEP minor (0.5%-1.0%)

Soot + ash results in large increase in FEP

100

engine

turbo

WWFEP

Estimated Euro III –

13 Mode Cycle Average

Conclusions

Additive Chemistry Effects on DPF Pressure Drop

Ash accumulation is a dynamic process –

Ash first primarily accumulates along channel walls before forming end plugs at the back of the DPF

Increase in DPF pressure drop 2X

more severe with Ca

ash than Zn

Similar ash properties and pressure drop trends between CJ-4 oil and Ca oil indicate CaSO4

may be most detrimental ash component

Ash + Soot Effects on DPF ΔP and Fuel Economy

Ash decreases pressure sensitivity to low soot loads (<0.5 g/l)

Ash increases pressure sensitivity for soot loads > 3g/l

Increase in pressure drop sensitivity most severe with fully-formulated oils

Ash alone results in only small increase in backpressure and fuel economy

Soot accumulated in ash-loaded DPF results in largest FEP

Acknowledgements

Research supported by: MIT Consortium to Optimize Lubricant and Diesel Engines for Robust Emission Aftertreatment Systems

We thank the following organizations for their support:

-

-

Caterpillar -

Chevron -

Ciba

-

Cummins

-

Detroit Diesel -

Komatsu

-

NGK

-

Oak Ridge National Lab -

Süd-Chemie

-

Valvoline

-

Ford

-

Lutek

MIT Center for Materials Science and Engineering