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The GDI Engine: Features, Emissions, and Effect of Fuel Composition
Allen L. Robinson Carnegie Mellon University
Funding: ARB, EPA, and CRC
Presented at Health Effects Institute Annual Conference, Alexandria VA, April 30-May 2, 2017.
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What is GDI?
Port Fuel Injection (PFI)
(Zim
mer
man
et a
l. ES
T 20
16)
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What is GDI?
GDI = Gasoline Direct Injection Port Fuel Injection (PFI)
GDI Benefits: (1) Higher compression ratio due to evaporative cooling effect
reducing compression temperature and knock onset (2) Greater flexibility in valve operations
~5% higher fuel economy
(Zim
mer
man
et a
l. ES
T 20
16)
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Wall vs. Spray Guided GDI
Spray Guided GDI Wall Guided GDI
(Zim
mer
man
et a
l. ES
T 20
16)
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GDI vehicles rapidly penetrating the fleet
5
• Market share of new vehicles with GDI >50% in 2016
5/15/2017
(Zim
mer
man
et a
l. ES
T 20
16)
New vehicle sales
On road fleet
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Rapid change in technology.
What are implications for emissions and air quality?
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Vehicle emissions in context
Increasingly stringent regulations (left) have led to large decreases in CO, NO, HC emissions from on-road fleet (right).
Slide from Tim Wallington, Ford, HEI Sponsors Meeting
Standards (HC + NOx) Emissions
(Dat
a fr
om B
isho
p, D
.H. S
tedm
an C
RC R
epor
t E-1
06, 2
014)
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Substantial improvements in ambient air quality
Large reductions in VOC concentrations measured in ambient air near Los Angeles from 1960-2010.
Slide from Tim Wallington, Ford, HEI Sponsors Meeting (Dat
a fr
om W
arne
ke e
t al.
JGR
2012
)
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Emissions and air quality
OH O3
hυ
deposition
NO3
Near Source Urban Regional (~ m) (1-10 km) (100+ km)
Spatial Scale
(1) Emissions at the tailpipe
(2) Downwind & urban scale
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GDI vs. PFI: No differences in emissions regulated gaseous pollutants
Increasing stringent standards
Hydrocarbons
CO
(Sal
iba
et a
l. ES
T 20
17)
LEV = low emission vehicle ULEV = ultra-low-emission vehicle SULEV = super ultra-low emission vehicle
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PFI vs. GDI -- No systematic changes in composition of organic gas emissions
(Sal
iba
et a
l. ES
T 20
17)
Increasing stringent standards
BTEX Emissions
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PFI PM emissions going down
(Sal
iba
et a
l. ES
T 20
17)
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PFI PM emissions going down
(Sal
iba
et a
l. ES
T 20
17; M
cDon
ald
EST
2014
)
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GDI have higher PM emissions than PFI
• Changes driven by elemental carbon (EC)
• Lower PM emissions for newer GDI
• Will GDI meet LEV3 standard?
(Sal
iba
et a
l. ES
T 20
17)
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GDI PM emissions dominated by Elemental Carbon (EC)
Elemental Carbon (EC)
Primary organic aerosol (POA)
(Sal
iba
et a
l. ES
T 20
17)
Some evidence for elevated PAH emissions.
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Differences in size distributions
0.00
0.05
0.10
0.15
0.20
0.25
5 50 500
dN/d
log(
dp)
Particle Size (nm)
PFI
GDI GDI
PFI
(Fig
ure
from
Imad
Kha
lek,
HEI
Fue
l Aro
mat
ic W
orks
hop
2016
)
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Lowering GDI PM Emissions
17
• GDI engine design & calibration is still improving
• Spray-guided GDI should reduce emissions
• Fuel reformulation
• Follow the diesel path: Gasoline particulate filters
5/15/2017
Exhaust Air
Fuel
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Fuel & soot (EC) formation processes
(Fig
ure
from
John
Far
rell,
HEI
Fue
l Aro
mat
ic W
orks
hop
2016
)
Hydrocarbon soot formation tendency: Paraffins < isoparaffins < mono-olefins < naphthenes < alkynes <aromatics
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Fuel effects on PM emissions: Particulate matter index (PMI)
DBE = double bond equivalents = (2C + 2 – H)/2 Wti = mass fraction of compound VP(443K) = vapor pressure at 443K (170ºC)
(Slid
e fr
om J
ohn
Farr
ell,
HEI F
uel A
rom
atic
Wor
ksho
p 20
16)
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Particulate Matter Index (PMI) works (surprisingly) well for conventional fuels
DBE = double bond equivalents = (2C + 2 – H)/2 Wti = mass fraction of compound VP(443K) = vapor pressure at 443K (170ºC)
PM (m
g/m
i) (Figure from Aikawa et al. SAE 2010-01-2115. )
PMI
Reducing aromatics in fuel generally reduces primary PM emissions (John Farrell, HEI Fuel Aromatic Workshop 2016)
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Ethanol and PM Emissions
PMI
PM (m
g/m
i)
EPAct – increasing PM in PFI Others have shown decreasing PM
E20
E10
E0
(Butler et al., SAE Technical Paper 2015-01-1072)
(Fro
m S
tore
y, H
EI F
uel A
rom
atic
Wor
ksho
p 20
16)
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Effects of gasoline particulate filter (GPF)
(Fro
m K
arav
alak
is, H
EI F
uel A
rom
atic
Wor
ksho
p 20
16)
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What about downwind of source?
OH O3
hυ
deposition
NO3
Near Source Urban Regional (~ m) (1-10 km) (100+ km)
Spatial Scale
(1) Emissions at the tailpipe
(2) Downwind & urban scale
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SOA
Evolution of Gases and Organic Aerosol
(Gor
don
et a
l. AC
P 20
14)
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Secondary PM production exceed primary emissions
(Gor
don
et a
l. AC
P 20
14; Z
hao
et a
l. in
pre
p) After ~1 hr of photo-oxidation
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Substantially less secondary PM production for alkylate fuel
(Zar
dini
et a
l. AE
201
4)
Alkylate Tests
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Conclusions Dramatic reductions in vehicle emissions over last four decades.
GDI vs. PFI: • At tailpipe:
• Similar gaseous emissions • GDI have higher PM emissions • Strategies for controlling PM
• Improved engine designs and operations • Fuel composition • Gasoline Particulate Filter
• Downwind:
• Similar secondary PM formation • Secondary PM >> primary PM emissions from light duty gas vehicle
(LDGV)
Important to control PM precursor emissions
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Acknowledgments CMU: Yunliang Zhao, Rawad Saleh, Georges Saliba, Albert Presto, Tim Gordon, Ngoc
Nguyen, Chris Hennigan, Andy May, Mrunmayi Karve, Shantanu Jathar, Yunliang Zhao, Neil Donahue, Peter Adams
ARB: Alváro Gutierrez, William H. Robertson, Mang Zhang, Oliver Chang, Shiyan Chen, Pablo Cicero-Fernandez, Bruce Frodin, Mark Fuentes, Shiou-Mei Huang, Richard Ling, Jeff Long, Christine Maddox, John Massetti, Eileen McCauley, Kwangsam Na, Yanbo Pang, Paul Rieger, Todd Sax, Satya Sardar, Tin Truong, Thu Vo, Christopher Brandow, Lyman Dinkins, Richard Ong Antonio Miguel, Sulekha Chattopadhyay, Hector Maldonado, Bob Torres, Eileen McCauley
UC Berkeley: Allen Goldstein, Greg Drozd Ford: Matti Maricq Financial Support:
• ARB – Contract #12-318 + Vehicle procurement, testing, and emissions characterization
• CRC A74/E96 – CMU smog chamber experiments • EPA STAR RD834554 – CMU primary emissions measurements • NSF – graduate student fellowships
This presentation reflects the views of the authors and not any of the funding agencies. No official endorsement should be inferred.