Emissions Testing Challenges for Plug in Hybrid Electric ...• PHV certification testing conducted...

Emissions Testing Challenges for Plug in Hybrid Electric VehiclesPlug‐in Hybrid Electric Vehicles

Dr. Tim Brown

Advanced Power and Energy Program

University of California IrvineUniversity of California, Irvine

California Clean Mobility Partnership• Collaborative effort supported by the California Air Resources

Board under the Alternative Fuel Incentive Program (AFIP) t d t f C lif i St t A bl Bill 1811 tenacted as part of California State Assembly Bill 1811 to assess

technical and social viability of vehicle electrification – Irvine and Berkeley campuses of University of California – Toyota Motor Engineering & Manufacturing North America, Inc.y g g g ,– Horiba, Ltd.

• PHV certification testing conducted by UC Irvine– Testing performed on Toyota Prius PHV “mule” vehicle

Testing assessed:– Testing assessed:• CVS and BMD system capabilitiesfor accurately measuring PHV emissions

d l f• Proposed California Air Resources Board PHV emissions certification procedure

4/12/2011Advanced Power and Energy Program, University of California, Irvine 2/26

CVS Testing Configuration

V hi l ti t ib d “d i l ” d t

Remote Mix Tee

Critical Flow

Venturi

• Vehicle negotiates prescribed “drive cycle” on dynamometer• Vehicle exhaust is mixed with ambient air such that total volume

flow rate is constant (hence CVS)• Exhaust and ambient air sample is collected in bags (Vmix)p g ( mix)• Post‐test, emissions species concentrations contained in the bags

are measured• Actual emissions masses are calculated based on measurement

and dilution factor (DF)


and dilution factor (DF)

CVS Emission Test for PHVs

2x Hybrid test = 4 UDDS = 8 Bags

UDDS 4

UDDS 3UDDS 2UDDS 1

10 minBag Read 10 minUDDS 4>30 minutes

Bag # 1 2 3 4 5 6 7 8


Bag # 1 2 3 4 5 6 7 8

PHV Operation

• PHEV charge depleting on UDDS1,25

10

-5

0

/mph

Battery Ah

Speed/10

Speed

Battery SOC

-15

-10Spe

ed/ Speed/10

FFM

y

FFM

0 500 1000 1500 2000 2500 3000 3500-25

-20

• Engine operates less than 1/3 in UDDS 1 (low exhaust, high DF)d

0 500 1000 1500 2000 2500 3000 3500time/s0 500 1000 1500 2000 2500 3000 3500

Time (seconds)


• HEV mode in UDDS 2,3,4

PHEV Emission Measuremente of

Engine Start Bag 1 contains important cold start emissions combined with much ambient air,

leading to a high dilution ratio and low

ttery State

Charge

All Electric Charge

Depleting Bl d d Ch S t i i (H b id)

emission concentrations

Bat Depleting Blended Charge Sustaining (Hybrid)

CO2

Vehicle

mission

s

CVS Bag 1CVS Bag 1CVS Bag 1 CVS Bag 2CVS Bag 2CVS Bag 2 CVS Bag 3CVS Bag 3CVS Bag 3

CO2Pollutants

Distance Traveled

V Em


Distance Traveled

CVS Testing Configuration Test Configuration

SmoothApproach

OrificeFuel Flow M t

Remote Mix Tee

Critical Flow

Meter

1. FFM used for CO2 comparison2. SAO used for Dilution Factor Calculation

Mix Tee Flow Venturi

Test Cycles1. UDDS2 HWFET


2. HWFET

CVS/PHV IssuesThree issues uncovered when using CVS for PHV

• Error associated with EPA dilution factor calculation assumptions is magnified by low vehicle emissions

• High DF and Vmix reduce measurement accuracy

• CO2 measurement discrepancy between CVS and FFM


Dilution Factor CalculationMass of Emission Species

Total Bag Volume

Sample Density

Emission Sample

Concentration

Ambient Sample

Concentration

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ −−=

DFCCVM ambsammix

11ρ

p

CCV %413

⎦⎣ ⎠⎝ DFDilution Factor

Ctp is not measured;

assumed to be 13.4%

For the first bag in a PHV test, CO2

samambsam

ambtp

tp

mix

CCCCC

VVDF %4.13

=−

−=≡

concentration may be less than 0.1%. Ambient

COVolume Emitted from

Tailpipe

Ambient CO2Concentration is Neglected in

EPA calculation

CO2concentration is 0.04%‐0.05%.


Tailpipe EPA calculation

DF Calculation Error

140

160

80

100

120

A DF Large DF Error

t Hi h DF

20

40

60EPA

Small DF Error at

at High DF (common for

PHEV)

0

0 50 100 150 200 250 300 350

EPA DF (accounting for ambient CO2)

Low DF

( g 2)• For Toyota PHV mule testing:

– DF error caused very small emission mass errors for all species except for THC– The relative THC mass error was 20% for UDDS cycles and up to 80% in HWFET cycles

• However because the PHV is so “clean” this only amounted to 4 7% of the SULEV NMOG standard


However, because the PHV is so clean , this only amounted to 4.7% of the SULEV NMOG standard

Solutions to DF Error • Three solutions exist:

– Use EPA calculation with ambient CO2

C413

Use Continuous Sampling system to determine C

ambsam

ambCOEPA CC

CDF−−

=+4.13

2

– Use Continuous Sampling system to determine Csam

∫= dVCV

C conticontiavg1

.amb

COEPA CCCDF −

=+4.13

2

– Calculate DF using SAO

∫Vmix ambcontiavgCOEPA CC −+

.2

SAOmix

mixSAO VV

VDF−

=SAOmixtp VVV −=tp

mixEPA V

VDF ≡


Solutions to DF Error

300

350

DFSAO

250

300

, DF E

PA

DFcontiDFEPA

150

200

AO, D

f con

ti,

50

100

DF S

A

0

0 50 100 150 200 250 300 350

DFEPA (Ambient CO2)


EPA ( 2)

Large Vmix

• CVS calculation

⎤⎡ ⎞⎛ 1⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ −−=

DFCCVM ambsammix

11ρ

– Any error from the MEXA gas analyzer or DF can be amplified by a large Vmix

I th PHV h d l ti l th CVS l l t f– In the PHV charge depleting cycle, the CVS samples a large amount of ambient air before the engine starts, resulting in a DF over 100

Theoretically a reduction in V can decrease the influence of– Theoretically, a reduction in Vmix can decrease the influence of potential error from MEXA and DF.


Alternative Procedure

60 60 Batter SOC

• Alternative procedure in charge depleting cycle eliminates the period before the engine first starts

40

50

Battery Ah*10SpeedFFMConti CO2

All electric

60

50

40

Battery SOCSpeedFFMConti CO2

10

20

30

spee

d/m

ph

30

20

10ed (m

ph)

-10

0

s

E i

10

0

‐10

Spee

200 400 600 800 1000 1200 1400-30

-20

time/s

Engine on‐20

‐30200 400 600 800 1000 1200 1400


Time (seconds)


60

• Calculation

60 Batter SOC

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−−=

2,2,2

11DF

CCVM ambsammixρ

40

50


60

50

40


10

20

30

spee

d/m

ph

30

20

10ed (m

ph)

-10

0

s

C2,sam (Conti)C1,amb (Conti)

10

0

‐10

Spee

200 400 600 800 1000 1200 1400-30

-20

time/s

t1 t2‐20

‐30200 400 600 800 1000 1200 1400C12,amb (Bag Sample)


Time (seconds)


60 60 Batter SOC

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−−=

2,2,2

11DF

CCVM ambsammixρSAOmix

mix

ambsam

amb

VVV

orCC

CDF

,2,2

,2

,2,2

,22

4.13−−

−=( ) ( )

2

1,121,12,2 t

tCttCC ambamb

amb

−+=

40

50


60

50

40


10

20

30

spee

d/m

ph

30

20

10ed (m

ph)

-10

0

s

C2,sam (Conti)C1,amb (Conti)

10

0

‐10

Spee

200 400 600 800 1000 1200 1400-30

-20

time/s

t1 t2‐20

‐30200 400 600 800 1000 1200 1400C12,amb (Bag Sample)


Time (seconds)


100

120

140

ctor

EPA procedure

New procedure

40

60

80

lution

Fac

0

20

40

TEST 1 TEST 2 TEST 3 TEST 4

Dil

• For Toyota PHV in charge depleting cycle, alternative procedure can reduce DF to ~30 by reducing Vmix, while for

TEST 1 TEST 2 TEST 3 TEST 4

p y g mix,EPA procedure DF is 3 to 4 times higher

• Can only be used for PHVs with “all‐electric mode”, not for blended PHVs


blended PHVs

CO2 Comparison• A fuel flow meter (FFM) was used as an independent

measurement device to compare CVS results • CO from FFM and CVS compared by carbon balance:• CO2 from FFM and CVS compared by carbon balance:

1244

,2

××=

tionCarbonFracMCO fuel

FFM

1244

2844

2,2××

+×

+=tionCarbonFracTHCMMCO CO

COCVS

SAO

FFM

RMT Venturi

CVSBagRack

FFM


Venturi

CO2 in UDDS1

500

Test Cell 2

CVS500

Test Cell 1

CVS

400

450

O2(grams) FFM

400

450

O2(grams) FFM

300

350

TEST 1 TEST 2 TEST 3

CO

300

350

TEST 1 TEST 2 TEST 3

CO

• In UDDS1, FFM consistently measured ~13 grams more CO2 than CVS (roughly 4%).

• For UDDS 2 3 and 4 FFM and CVS measured within 1% and showed noFor UDDS 2,3, and 4, FFM and CVS measured within 1% and showed no consistent trend


FFM Compared to CVS in UDDS1

40

50

SAO Exhaust FlowFFM CO2

50

40

FFM CO2SAO flowS d

30

40

mph

SpeedConti CO2

ph) 30

SpeedConti CO2

10

20

spee

d/m

Speed (m 20

10

10

00

‐101000 1050 1100 1150 1200 1250 1300 1350 1400-10

time/s

1000 1050 1100 1150 1200 1250 1300 1350 1400‐10

Time (seconds)


6 Engine starts

FFM Compared to CVS in UDDS1

40

50

SAO Exhaust FlowFFM CO2SpeedConti CO2

FFM CO2SAO flowSpeed

20

30

spee

d/m

ph

Conti CO2Conti CO2

-10

0

10s

1000 1050 1100 1150 1200 1250 1300 1350 1400-10time/s

101520

ms)

FFM minus CVS

‐50510

1 2 3 4 5 6CO2(gra


Engine starting number in UDDS1

Gas Sampling• In the tailpipe and CVS line before RMT, Compare the initial and final condition in UDDS1.

1.Ambient air2 Exhaust gas

SAO

2. Exhaust gas

CVSBag

FFM

1. Initial condition: ambient air;

RMT Venturi

BagRack

;

2. Final condition: exhaust gas.

3. CVS samples some ambient air and leaves exhaust gas in the first cycle.


Gas Sampling• In the tailpipe and CVS line before RMT, Compare the initial and final condition in UDDS2.

1. Exhaust gas left in the first cycle2. Exhaust gas generated in the second

cycle

SAO

cycle

CVS

FFM

1. Initial condition: exhaust gas left in the first cycle;

RMT Venturi

BagRack

g y ;

2. Final condition: exhaust gas generated in the second cycle.

3. CVS samples some of the exhaust gas belonging to the previous cycle and leaves some of the exhaust gas belonging to the current cycle


and leaves some of the exhaust gas belonging to the current cycle.

Conclusions

1. Assumptions in EPA DF calculation can result in higher gas mass for PHV. The error for THC is significant. DFSAO and DFEPA(with ambient CO2)The error for THC is significant. DFSAO and DFEPA(with ambient CO2) provide more accurate alternative. DFSAO can be a potential new DF measurement for PHV test procedure.

2. CVS continuous sampling method for charge depleting cycle can reduce DF to around 30, thus reducing the impact of possible error from MEXA and DF.

3. CVS and FFM show good CO2 agreement in UDDS 2, 3, and 4. In UDDS 1, CVS measures around 13 grams lower CO2 than FFM. Residual ambient air volume upstream of the gas analyzer may be the reasonair volume upstream of the gas analyzer may be the reason.


Acknowledgment

• Zhang, Li– UC Irvine Master’s Student who conducted testing and data analysis

• Horiba• Toyota• California Air Resource’s BoardCalifornia Air Resource s Board


Emissions Testing Challenges for Plug in Hybrid Electric VehiclesPlug‐in Hybrid Electric Vehicles

Dr. Tim Brown

Advanced Power and Energy Program

University of California IrvineUniversity of California, Irvine

Emissions Testing Challenges for Plug in Hybrid Electric ...• PHV certification testing conducted...

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