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
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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