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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)
4/12/2011Advanced Power and Energy Program, University of California, Irvine 3/26
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 4/26
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)
4/12/2011Advanced Power and Energy Program, University of California, Irvine 5/26
• 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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 6/26
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 7/26
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 8/26
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%.
4/12/2011Advanced Power and Energy Program, University of California, Irvine 9/26
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 10/26
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 ≡
4/12/2011Advanced Power and Energy Program, University of California, Irvine 11/26
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)
4/12/2011Advanced Power and Energy Program, University of California, Irvine 12/26
EPA ( 2)
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 13/26
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.
4/12/2011Advanced Power and Energy Program, University of California, Irvine 14/26
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 15/26
Time (seconds)
Alternative Procedure
60
• Calculation
60 Batter SOC
⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛−−=
2,2,2
11DF
CCVM ambsammixρ
40
50
Battery Ah*10SpeedFFMConti CO2
60
50
40
Battery SOCSpeedFFMConti CO2
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)
4/12/2011Advanced Power and Energy Program, University of California, Irvine 16/26
Time (seconds)
Alternative Procedure
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
Battery Ah*10SpeedFFMConti CO2
60
50
40
Battery SOCSpeedFFMConti CO2
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)
4/12/2011Advanced Power and Energy Program, University of California, Irvine 17/26
Time (seconds)
Alternative Procedure
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 18/26
blended PHVs
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 19/26
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 20/26
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 21/26
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)
4/12/2011Advanced Power and Energy Program, University of California, Irvine 22/26
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 23/26
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.
4/12/2011Advanced Power and Energy Program, University of California, Irvine 24/26
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 25/26
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.
4/12/2011Advanced Power and Energy Program, University of California, Irvine 26/26
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
4/12/2011Advanced Power and Energy Program, University of California, Irvine 27/26
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