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.

What is GDI?

Port Fuel Injection (PFI)

(Zim

mer

man

et a

l. ES

T 20

16)

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

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et a

l. ES

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16)

Wall vs. Spray Guided GDI

Spray Guided GDI Wall Guided GDI

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et a

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GDI vehicles rapidly penetrating the fleet

5

• Market share of new vehicles with GDI >50% in 2016

5/15/2017

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et a

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New vehicle sales

On road fleet

Rapid change in technology.

What are implications for emissions and air quality?

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)

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

)

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

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

PFI vs. GDI -- No systematic changes in composition of organic gas emissions

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et a

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T 20

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Increasing stringent standards

BTEX Emissions

PFI PM emissions going down

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iba

et a

l. ES

T 20

17)

PFI PM emissions going down

(Sal

iba

et a

l. ES

T 20

17; M

cDon

ald

EST

2014

)

GDI have higher PM emissions than PFI

• Changes driven by elemental carbon (EC)

• Lower PM emissions for newer GDI

• Will GDI meet LEV3 standard?

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iba

et a

l. ES

T 20

17)

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.

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

)

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

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

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)

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)

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)

Effects of gasoline particulate filter (GPF)

(Fro

m K

arav

alak

is, H

EI F

uel A

rom

atic

Wor

ksho

p 20

16)

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

SOA

Evolution of Gases and Organic Aerosol

(Gor

don

et a

l. AC

P 20

14)

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

Substantially less secondary PM production for alkylate fuel

(Zar

dini

et a

l. AE

201

4)

Alkylate Tests

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

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.