1

On-road particle and gaseous emissions from a

PFI and GDI hybrid electric vehicle (in the winter)Jacob Swanson1, Chengguo Li2, Shaohua Hu3, Shishan Hu3,

Liem Pham2, Heejung Jung2

1Minnesota State University, Mankato2University of California, Riverside

3California Air Resources Board

In 2012, the ARB adopted the Advanced Clean Cars program, which

included an increased zero-emissions vehicles (electric vehicles and

hydrogen fuel cell vehicle), and hybrid electric vehicles for MY 2018

through 2025

Mobile sources strategy from ARB

2

Most previous HEV studies were

conducted at modest temperatures

Hu et al. 2016- Two PHEVs (PFI) vs 2015 GDI conventional vehicle on chassis dyno (~20°C)

- PFI has lower emissions of CO2, PM mass and particle compared to GDI

engine

- Cold start particle emissions still represent the majority of particle emissions

ARB report. 2017 - On-road test under the ambient temperature (~20°C)

- 2013 Toyota Prius PHEV(PFI) vs 2016 Hyundai Sonata PHEV (GDI

- The GDI engine has higher NOx + HC emissions than that of PFI engine

Holmen et al. 2014

- On-road test under the ambient temperature (summer and winter, 0~35oC)

- 2010 Toyota Camry vs 2010 Camry HEV (GDI)

- Re-ignition HEV of PN >> Stable HEV of PN, Re-ignition high 30-70 nm

emissions

3

4

Research objectives for tests conducted in cold

weather in MN winter (Feb, -3°C ± 3)

• Compare cold weather on-road emissions between PFI

engine and GDI engine

• Compare “Cold cold” starts with “re-ignition events” on city

and highway drive cycles

• Evaluate the impact of “re-ignition” events on maintaining

catalyst temperature

HEVs specifications and instruments

Vehicle specifications (HEVs)

Toyota Prius Hyundai Sonata

Year 2016 2015

Engine Type 1.8L, I4, 121 hp 2.4L, I4 199 hp

MPG 54 city, 50 highway 36 city, 40 highway

Electric motor 60 hp 47 hp

Battery output 45kW 47kW

Fuel injection PFI GDI

Gasoline engine 71 hp @4800 rpm 159 hp @ 5,500 rpm

5

Instruments

• EEPS: dilute particle number-total and size

• E-filter – charged particles

• Thermal dilutor: total and solid particles

• NGK/NTK tailpipe sensor

- NOx emissions, PN concentration, PM concentration

Dekati e-filter is a diffusion charger

combined with a gravimetric filter

6𝐌𝐚𝐬𝐬 scales with total 𝐜𝐮𝐫𝐫𝐞𝐧𝐭

NTK/NGK PM/PN raw tailpipe sensor

7

Particle and gas sampling apparatus

8

EEPS

e-Filter

Thermo-dilutor

control unit (350°C)

Dilutor

Heat

controller

NTK/

NGK

Tailpipe

Heating line

Sampling probe

NOx sensor

PN/PM

sensor

Outside car Inside

9

Example time series of driving data

10

0

5

10

15

20

EEPS

2000 2500 3000 3500 4000

RPM Speed

Multiple days of prescribed city and highway drive cycles

(2 hr / each)

About 1 “re-ignition” event per minute (Prius)

Frequency and duration of re-ignition events

for Prius and Sonata were very different

0

5

10

15

20

25

30

0 50 100 150 200 250 300 350 400

Prius HEV_CityPrius HEV_HighwaySonata HEV_CitySonata HEV_Highway

Fre

qu

en

cy

Re-ignition duration time (s) 11

Catalyst temperatures do not drop below the

expected light-off temperature

300

400

500

600

700

800

1000 2000 3000 4000 5000 6000

Sonata HEVPrius HEV

Ca

taly

sts

Te

mp

era

ture

(oC

)

Time (s)12

Particle number time series – Prius

0

5

10

15

20

25

0 1000 2000 3000 4000 5000 6000

Prius HEV (TPM)-City (Temp. 0oC~-2

oC)

Pa

rtic

le n

um

be

r ×

10

6 (

#/c

m3)

Time (s)

0

5

10

15

20

EEPS

2000 2500 3000 3500 4000

RPM Speed

0

0.5

1

1.5

2

150 200 250 300

Cold-cold start

Route-1 city 13

Particle number time series – Sonata

0

5

10

15

20

25

0 1000 2000 3000 4000 5000 6000

Sonata HEV (TPM)-City (Temp. -2oC~-6

oC)

Pa

rtic

le n

um

be

r ×

10

6 (

#/c

m3)

Time (s)

0

5

10

15

20

EEPS

2000 2500 3000 3500 4000

RPM

0

2

4

6

8

10

0 50 100 150 200 250 300

14

Cold-cold start

Particle mass time series

0

0.0001

0.0002

0.0003

0.0004

0.0005

0 1000 2000 3000 4000 5000 6000

Prius HEV (TPM)-City (Temp. 0oC~-2

oC)

Prius HEV (SPM)-City (Temp. 0oC~-2

oC)

PM

mass (

mg

/s)

Time (s)

0

0.0001

0.0002

0.0003

0.0004

0.0005

0 500 1000 1500 2000 2500 3000 3500 4000

Prius HEV (TPM)-Highway (Temp. -2oC~-7

oC)

Prius HEV (SPM)-Highway (Temp. -1oC~-3

oC)

PM

mass (

mg

/s)

Time (s)

0

0.0001

0.0002

0.0003

0.0004

0.0005

0 500 1000 1500 2000 2500 3000 3500 4000

Sonata HEV (TPM)-Highway (Temp. 0oC~-3

oC)

Sonata HEV (SPM)-Highway (Temp. 0oC~-4

oC)

PM

mass (

mg

/s)

Time (s)

0

0.0001

0.0002

0.0003

0.0004

0.0005

0 1000 2000 3000 4000 5000 6000

Sonata HEV (TPM)-City (Temp. -2oC~-6

oC)

Sonata HEV (SPM)-City (Temp. 0oC~-3

oC)

PM

mass (

mg

/s)

Time (s)

15

Summary of total particle number

emissions

0

1

2

3

4

5

Cold-cold start Re-ignition (City)

Re-ignition (Highway)

Prius HEV (PFI)

Sonata HEV (GDI)

Ave

rag

e p

art

icle

nu

mb

er

× 1

06 (

#/c

m3)

16

Summary of NOx emissions

0

20

40

60

80

100

120

140

Cold-cold start Re-ignition(City)

Re-ignition(Highway)

Prius HEV (PFI)

Sonata HEV (GDI)

Ave

rag

e N

Ox c

on

ce

ntr

atio

n (

pp

m)

17

Particle instrument correlations (r2)

Condition PN: EEPS vs NTK PM: EEPS vs NTK EEPS (PM) vs

E-current

City

Prius 0.80 0.46 0.40

Sonata 0.22 0.14 0.51

Highway

Prius 0.34 0.26 0.65

Sonata 0.08 0.01 0.31

Total particles (solid and semi-volatile)

18

Condition PN – EEPS vs NTK PM – EEPS vs NTK PM_EEPS vs E-

current

City

Prius 0.77 0.70 0.96

Sonata 0.38 0.27 0.85

Highway

Prius 0.22 0.22 0.95

Sonata 0.01 0.05 0.65

Only solid particles

Summary – re-ignition events and

catalyst temperature

• City

− Prius re-ignition events very short (10 s) and frequent

(every ~ 1 min)

− Sonata re-ignition events are ~ 75 s and less frequent

(every ~ 2 min)

• Highway

− Prius re-ignition events are ~ 45 s in duration

− Sonata re-ignition events are ~ 5 min in duration

For both vehicles, design and prevailing conditions result

in catalyst temperatures remaining well above light-off

temperatures always

→ re-ignition particle and NOx emissions are low

19

o Cold cold start emissions

• NOx: Sonata ~ Prius

• PM: Sonata ~ 5 x Prius

o City “re-ignition” emissions

• NOx: Sonata ~ 0.5 x Prius

• PM: Sonata ~ Prius

o Highway “re-ignition” emissions

• NOx: Sonata ~ Prius

• PM: Sonata ~ 2 x Prius

Summary – comparison of emissions

and instrument correlations

20

o EEPS number and mass did not correlate with

NGK/NTK number and mass, respectively

o EEPS mass correlated very well with E-filter – and I

expect even better correlation with Dp1.4

Re-ignition

emissions

generally higher

than cold start

Questions?

21

NOx emission from Prius HEV

Temp. 0 oC ~ -2 oC

Temp. 0 oC ~ -2 oC

Temp. -2 oC ~ -7 oC

Temp. -1 oC ~ -3 oC

22

NOx emission from Sonata HEV

Temp. -2 oC ~ -4 oC

Temp. -0 oC ~ -3 oC

Temp. 0 oC ~ -3 oC

Temp. 0 oC ~ -4 oC

23

PM cumulative mass

0

0.02

0.04

0.06

0.08

0.1

0.12

0 1000 2000 3000 4000 5000 6000

Prius HEV (TPM)Prius HEV (SPM)Sonata HEV (TPM)Sonata HEV (SPM)

Cu

mu

lative

Mass (

mg)

Time (s)

City

0

0.02

0.04

0.06

0.08

0.1

0.12

0 500 1000 1500 2000 2500 3000 3500 4000

Prius HEV (TPM)Prius HEV (SPM)Sonata HEV (TPM)Sonata HEV (SPM)

Cu

mu

lative

Mass (

mg)

Time (s)

Highway

24

➢ Prius HEV vs. Sonata HEV NOx emissions

-63% of NOx for Prius > Sonata when cold-cold start

-Re-ignition events during city and highway driving

:230 % of NOx emissions for Prius > Sonata (City)

:52 % of NOx emissions for Sonata>Prius (Highway)

➢ Prius HEV vs. Sonata HEV particle number (PN)

-300 % of PN for Sonata > Prius when cold-cold start

-Re-ignition events during city and highway driving

:53 % of PN emissions for Sonata > Prius (City)

:140 % of PN emissions for Sonata>Prius (Highway)

Summary – comparison of emissions

25

Specifications of the HEVs

Vehicle specifications (HEVs)

Toyota Prius Hyundai Sonata

Year 2016 2015

Engine Type 1.8L Hybrid I4 121hp 2.4L Hybrid I4 199hp 154ft. lbs.

MPG 54 city, 50 highway 36 city, 40 highway

Electric motor 60 hp 47 hp (35kW) @ 1,6303,000 rpm

Motor type/voltage Nickel-metal hydride

/123

Interior-Permanent Magnet

Synchronous Motor/270 V

Battery output 45kW 47kW

Battery type/voltage ZVW50 model (Nickel-Metal

hybride battery)/240 V

Lithium polymer battery/270 V

Fuel Injection PFI GDI

Gasoline engine 71 Ib-ft @4800 rpm 159 hp @ 5,500 rpm

Torque 120.2 Ib-ft @ 4000 rmp 154 Ib-ft @ 4,500 rpm

Transmission CVT 6-Speed Shiftable Automatic

Curb Weight 3075 Ibs 3,508 lbs

26

NTK/NGK_NOx sensor

27

Particle number-Contour

City-Prius HEV

(SPN)

City-Prius HEV

(TPN)

Highway-Prius HEV

(SPN)

Highway-Prius HEV

(TPN)

City-Sonata HEV

(SPN)

City-Sonata HEV

(TPN)

Highway-Sonata HEV

(SPN)

Highway-Sonata HEV

(TPN)

Temp. 0 oC ~ -2 oC

Temp. 0 oC ~ -2 oC

Temp. -2 oC ~ -4 oC

Temp. 0 oC ~ -3 oC

Temp. -2 oC ~ -7 oC

Temp. -1 oC ~ -3 oC

Temp. 0 oC ~ -3 oC

Temp. 0 oC ~ -4 oC

28

NOx vs RPM_Sonata HEV

0

50

100

150

200

250

300

2000 2200 2400 2600 2800 3000

NOx Concentration RPM

NO

x (

ppm

)

F

0

50

100

150

0

200

400

600

800

1000

0 200 400 600 800 1000 1200 1400

NOx concentrationSOC Catalysts temperature

NO

x (

ppm

) /

SO

C (

%)

Cata

lysts

tem

pe

ratu

re (o

C)

Time (s)

RPM

0

100

200

300

400

500

600

700

800

0

20

40

60

80

100

0 1000 2000 3000 4000 5000 6000

Catalysts TemperatureNOx ConcentrationSOC

NO

x (

pp

m)

/ C

ata

l.T

em

p. (o

C)

SO

C (%

)

Time (s)

Sonata HEV (City-1st)

Temp. -2 oC ~ -4 oC

29

On-road particle and gaseous

emissions from a PFI and GDI hybrid

electric vehicle (in the winter)

Jacob Swanson1, Chengguo Li2, Shaohua Hu3, Shishan Hu3,

Liem Pham2, Heejung Jung2

1Minnesota State University, Mankato2University of California, Riverside

3California Air Resources Board

2017 Cambridge Particle Meeting, 23 June 2017

Non-ignition events during RPM=0

400

450

500

550

600

650

700

750

800

Prius (City) Prius (Highway) Sonata (City) Sonata (Highway)

Ca

taly

sts

Te

mp

era

ture

(oC

)

31

Example linear correlations between EEPS and NTK

Total particle Solid particle

City

Hig

hw

ay

32

Linear correlation between EEPS and NTK for

Sonata

Total particle Solid particle

City

Hig

hw

ay

33

Linear correlation between EEPS and e-Filter

34

PM number (EEPS)

0

5

10

15

20

25

0 1000 2000 3000 4000 5000 6000

Prius HEV (TPM)-City (Temp. 0oC~-2

oC)

Prius HEV (SPM)-City (Temp. 0oC~-2

oC)

Pa

rtic

le n

um

be

r ×

10

6 (

#/c

m3)

Time (s)

0

5

10

15

20

25

0 500 1000 1500 2000 2500 3000 3500 4000

Prius HEV (TPM)-Highway (Temp. -2oC~-7

oC)

Prius HEV (SPM)-Highway (Temp. -1oC~-3

oC)

Pa

rtic

le n

um

be

r ×

10

6 (

#/c

m3)

Time (s)

0

5

10

15

20

25

0 1000 2000 3000 4000 5000 6000

Sonata HEV (TPM)-City (Temp. -2oC~-6

oC)

Sonata HEV (SPM)-City (Temp. 0oC~-3

oC)

Part

icle

num

be

r ×

10

6 (

#/c

m3)

Time (s)

0

5

10

15

20

25

0 500 1000 1500 2000 2500 3000 3500 4000

Sonata HEV (TPM)-Highway (Temp. 0oC~-3

oC)

Sonata HEV (SPM)-Highway (Temp. 0oC~-4

oC)

Part

icle

nu

mb

er

× 1

06 (

#/c

m3)

Time (s)

35

Particle size distribution

0

5 106

1 107

1.5 107

2 107

1 10 100 1000

Prius HEV (TPN)Prius HEV (SPN)Sonata HEV (TPN)Sonata HEV (SPN)

dN

/dL

ogd

p (

#/c

m3)

Size (nm)

City

0

5 106

1 107

1.5 107

2 107

1 10 100 1000

Prius HV (TPN)Prius HV (SPN)Sonata HV (TPN)Sonata HV (SPN)

dN

/dLogd

p (

#/c

m3)

Size (nm)

Highway

36

Time constant for cool down and warm-

up

37

0

20

40

60

80

100

120

Warm-up Cool-down

Tim

e c

on

sta

nt

(s)

38