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WE START WITH YES.
SOOT OXIDATION IMPACTED BY ENGINE OIL-DERIVED ASH FROM A GASOLINE DIRECT
INJECTION ENGINEApril 8, 2016
Heeje Seong and Seungmok Choi
Argonne National Laboratory
Jimmie L. Williams
Crystalline Materials Research, Corning Incorporated
Jung-Min Seo and Chi-Bum In
Exhaust Emission Engineering Team, Hyundai Motor Company
Bill Lam and Huifang Shao
Afton Chemical
2016 Cross-Cut Lean Exhuast Emissions Reduction Simulations (CLEERS) Workshop
BACKGROUND
2
With the increased PM emissions from GDI engines, GPFs have been
recognized to be enabling technologies to meet future PM emission standards
Considering factors
for particulate filters
Diesel engine
(lean)
GDI engine
(stoichiometric)
Exhaust temperature Low High
Regeneration
Active (post injection
or heater)Passive
Passive (NO2
generation)
Catalysts Oxidation catalysts TWC
Limitation Low temperature
Extremely low O2 &
NO2
Sensitive ∆P
“Add-on” GPF “All-in-one” GPF
Dow, 2010
MECA, 2013
3
BACKGROUND (CONT’D)
0
20
40
60
80
100
0 50 100 150 200
Printex U
LD Diesel_Ash 0.36%GDI_Ash 0.10%GDI_Ash 0.58%GDI_Ash 1.35%GDI_Ash 3.36%GDI_Ash 17.27%
m/m
0 [
%]
Time [min.]
Increase of
ash fraction
TGA isothermal oxidation
(600 °C, 8% O2, pre-treated by N2)
Engine oil-derived ash creates negative impacts on TWC performance and
back-pressure, while it can enhance soot oxidation
ANL, 2014 CLEERS
MIT, SAE 2009-01-1086
POSTECH, 2009 App. Cat. B: Env.
OBJECTIVES
Evaluate ash composition-dependent soot oxidation and find oxidation
mechanisms.
Identify ash chemistries that could influence soot and catalysts.
APPROACH & CHARACTERIZATION
4
Soot oxidation experiments and bench-
scale filter tests (2”(D)x6”(L))2.4L GDI Engine
TGA
DSC
Characterization of GDI soot
and filter substrates
(APS, CNM, UIUC)
Gravimetric
sampling
In-line filter
Formulated engine oils were dosed into fuel
(accelerated oil injection: 2% in fuel)1. Ca-, P- & P-Zn-specific engine oils (ANL only)
2. Ca/Mg/Zn/P formulated experimental engine oils designed by matrix
(Afton supplied)
5
Based on major additive components, Ca-, P- & Zn-P-specific engine oils were formulated (ANL only)
ICP analysis:
0
500
1000
1500
2000
2500
3000
3500
Non-detergent(SAE30)
Gasoline(5W20)Conventional
Gasoline(5W20)Synthetic
Gasoline(5W20)Longer life
Diesel(15W40)
Co
nce
ntr
atio
n (
pp
m)
Na
Ca
Mg
B
Zn
P
Mo
4,659 ppm 3,805 ppm 5,212 ppm 6,780 ppm646 ppm
Ca source: Calcium dodecyl-benzene
sulfonate
P source: Triethyl phosphite
Zn & P: Zinc dithiophosphate
(ZDDP)
Dosage in fuel (ppm) Ca Zn P Na Total
Gasoline Only 0.0
1% Non-detergent oil 0.4 3.3 2.7 6.4
1% Conventional oil 21.2 11.0 9.6 4.6 46.5
Calcium Sulfonate
in 1% non-detergent oil4 – 24 4 – 24
Phosphite
in 1% non-detergent oil18 – 55 18 – 55
Zinc Dialkyl Dithiophosphate (ZDDP)
in 1% non-detergent oil8 – 206 8 – 191 16 – 397
Matrix design of oil formulations helps better understand effects of Ca(Mg)/ZDDP ratios on soot oxidation
6
Experimental Oil
Samples (Afton
Supplied)
Ca-LL Mg-LL Ca-LH Mg-LH Ca-HL Mg-HL Ca-HH Mg-HH
Boron, ppm 180 180 180 180 180 180 190 180
Calcium, ppm 1100 1 780 0 2670 3 2360 1
Magnesium, ppm 8 680 3 480 9 1680 8 1420
Phosphorus, ppm 600 600 1220 1220 600 610 1210 1170
Zinc, ppm 710 710 1430 1430 700 720 1410 1380
Sulfated Ash, % 0.56 0.51 0.65 0.63 1.02 0.93 1.1 0.96
Ca/(P+Zn) or Mg/(P+Zn), molar 0.91 0.93 0.32 0.32 2.21 2.25 0.97 0.97
0
20
40
60
80
100
0 50 100 150
Ca-LL
Ca-HL
Ca-HH
Ca-LH
Mg-HL
Mg-LL
Mg-LH
Mg-HH
So
ot
rem
ain
ing
mass
(%
)
Time (min)
t800
10
20
30
40
50
0 0.5 1 1.5 2 2.5
CaMg
t80
(m
in)
Ca(or Mg)/(P+Zn), molar ratio
More reactive
2016 © Afton Chemical Corporation, All Rights Reserved. Not to be copied, shared, or reproduced in any media without the express written permission of Afton Chemical Corporation.
7
Soot oxidation enhanced with Ca, while deteriorated with P
TGA: isothermal 600ºC, 8% O2
0
20
40
60
80
100
0 100 200 300 400 500
Non-detergent oil 1%
Conv. oil Ash 3.7%
Conv. oil Ash 23.4%
Ca Ash 3.5%
Ca Ash 5.8%
P Ash 3.2%
P Ash 5.6%
ZDDP Ash 8.5%
ZDDP Ash 16.7%
Carb
on
so
ot
mass (
%)
Time (minutes)
Impact on soot oxidation
by 1.0 wt.% of ash fraction in soot
Ca +14.5%
P -15.4%
ZDDP (Zn+P) -13.7%
Conv. oil +11.1%
Baseline: non-detergent oil 1%
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.5 1
△m
/min
stan
t((
mg/
min
)/m
g)
Conversion (α)
Non-detergent oil 1%
Conv. Oil 2% - 93 ppm
Ca 24 ppm
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 0.5 1
△m
/min
stan
t((
mg/
min
)/m
g)
Conversion (α)
Non-detergent oil 1%
P 36.5 ppm
ZDDP 109.2 ppm
Testing set-up that enables aging test and realistic GPF conditions has been built
8
Engine oil tank
Air heater
GPF
GPF system
In-line GPF setup (2”(D)x6”(L))- No visualization
- Hot exhaust T as actual test
- No sealing problem
Dilution setup and emissions measurements
- Quick access: 3-way valve for fast measurements
Lube-oil injection system
- Aging test enabled
∆P decrease in the initial regeneration stage confirms ash-induced continuous regeneration
9
Ash loading
- Engine oil: conventional 5W20
- Oil consumption rate: 2% in fuel
- Operated at 1250 rpm – 25% load
Continuous regeneration
- When the initial soot loaded was 0.45 g/L, exhaust temperatures were increased by
changing the engine operation mode (2000 rpm – 50% load)
- After soot burning at the initial stage, soot loading resumed
- Slow soot oxidation with no ash even at 550°C due to the extremely low O2 availability
Continuous operation
80
85
90
95
100
0
50
100
150
200
250
300
0 0.1 0.2 0.3 0.4 0.5
Filt
rati
on
eff
icie
ncy
(%
)
Pre
ssu
re d
rop
(kP
a/(m
3/s
ec))
Soot loading (g/L)
△P - W/O Ash
△P - Ash 2.0 g/L
FEmass - W/O Ash
FEmass - Ash 2.0 g/L
Soot mass: 10 mg/m3
Filter: HP200/12-2X
GPF inlet temperature: 550°C
O2, in: 1.5%
Initial soot loading: 0.45 g/L
Soot conc.: 1.0 mg/m3
Synchrotron XRPD indicates that ash derived from Ca sulfonate is CaSO4, which indeed enhances oxidation
10
Sample preparation: - Tight contact: grinding in agate mortar
CaSO4 impact is significant- BET S.A.: Drierite > CaSO4 (S-A)
- BET surface area seems to affect oxidative reactivity
(drierite: 10 m2/g, CaSO4 (S-A): 2 m2/g)
MIT, SAE 2009-01-1086
Ash from field-aged DPF
Sulfur K-edge XANES results suggest that sulfur oxidation states vary during soot oxidation
11
-5.00E-01
0.00E+00
5.00E-01
1.00E+00
1.50E+00
2.00E+00
2.50E+00
3.00E+00
3.50E+00
2460 2470 2480 2490 2500 2510
CaSO4_fresh
CaSO4_50%
CaSO4_100%
-1.00E+00
0.00E+00
1.00E+00
2.00E+00
3.00E+00
4.00E+00
2460 2470 2480 2490 2500 2510
K2SO4_fresh
K2SO4_50%
2471.4 keV
Sample preparation:
- Tight contact by grinding in mortar
- 0%, 50% & 100% oxidized at 600°C
- Ex-situ XANES analysis in APS at ANL
S K-edge XANES:
- 0%-oxidized CaSO4 is actually hydrated form
- 50% oxidized samples only
- Small hump at 2471.4 keV: 1+ oxidation
- Suggest a potential variation of sulfur oxidation
states during oxidation
- In-situ experiments will be performed.
Bare, 2005 APS
However, the presence of sulfur is not clear in GDI engine tests
12
SEM-EDS result of soot collected from Ca-LH case (p. 9)
CaseAtomic %
Ca P Zn S
Ca
additive
1.23 0 0 0
P
additive
0 2.83 0 0
ZDDP 0 2.88 0.08 0
150155160165170175180
S 2P in soot from Ca additiveS 2P in soot from P additiveS 2P in soot from ZDDP
XPS result of soot samples (p. 6)
AlP Ca
Ce
ZrCu(from grid)
Zn
TEM-EDS result of ash taken
from a field-aged GPF
PCa
Cu(from grid)
Zn
TEM-EDS result of ash derived
from engine oil in GDI engine
P
Ca
Zn Ca
Oil matrix dependent on Ca(Mg)/ZDDP ratios affects ash composition and soot residue
13
400 800 1200 1600 2000 2400 2800
Inte
ns
ity
(A
.U.)
Raman shift (cm-1
)
Carbon
Ca-HL
Mg-HH
Ca-HH
Mg-LH
Ca-LH
Mg-HL
ZnO
(M)CO3
Samples:- Ash remained after oxidation completed
UV-Raman (325 nm)
Soot still remained with ash- Except Ca-HL case, soot was present
May contribute to increased ∆P
Ash compositions influenced- High Ca(Mg)/ZDDP cases appear to
generate ZnO.
- Low Ca/ZDDP case generates –CO3
compounds.
2016 © Afton Chemical Corporation, All Rights Reserved. Not to be copied, shared, or reproduced in any media without the express written permission of Afton Chemical Corporation.
Amorphous nuclei particles from engine oil might convert into crystalline agglomerates with oxidation
14
Amorphous particles
(no crystallites)
Metal crystallitesMetal crystallites
Raw particlesash remained after
soot oxidation
The nature of nuclei particles derived from engine oil has been rarely examined.
While most nuclei particles in the sub-20-nm were observed to be amorphous metal
particles, ash agglomerates in the sub-micron were metal crystallites.
Suggest phase conversion from amorphous into crystalline state during oxidation
Major elements of sub-20-nm particles were observed to be P and Ca
Need more investigation when the engine is run at high speed & load
Will inform ash chemistries affecting TWC functionality
1250rpm-25% load
Nuclei particles
(<20nm)
Dark-field STEM
CONCLUSIONS
15
Soot oxidation enhanced by engine oil-derived ash is closely related to
the increased ratio of Ca to Zn & P in engine oil.
− Ca additive is more impactful than Mg additive.
− Soot oxidation reactivity is much dependent on Ca (or Mg) to ZDDP ratios,
regardless of contents of Ca, Mg, Zn and P.
Ash chemistries seem to be appreciably influenced by oil matrix.
− ZnO with high Ca(Mg)/ZDDP
− Carbonate (-CO3) with low Ca/ZDDP
The major ash compound, CaSO4, from diesel engines could contribute
little to ash from GDI engines.
− Sulfur element was rarely observed with XPS, SEM-EDS and TEM-EDS.
Amorphous ash nanoparticles may convert into crystalline agglomerates.
− Nanoparticles in the sub-20-nm range are mostly Ca and P, while S and Zn
were rarely observed.
ACKNOWLEDGEMENTS
Funding
- U.S. DOE Office of Vehicle Technologies, Ken Howden and
Gurpreet Singh
use of the Center for Nanoscale Materials and Advanced Photon
Sources was supported by the U. S. DOE Office of Science,
Office of Basic Energy Sciences, under Contract No. DE-AC02-
06CH11357.
XPS analysis was performed in UIUC-MRL.
All rights from oil matrix and related results are reserved for Afton
Chemical Corporation.
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