Cooled EGR and alternative fuels V1 - Mechanical...
Transcript of Cooled EGR and alternative fuels V1 - Mechanical...
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Engine, Emissions and Vehicle Research DivisionSouthwest Research Institute
Engine, Emissions and Vehicle Research DivisionEngine, Emissions and Vehicle Research DivisionSouthwest Research InstituteSouthwest Research Institute
Cooled EGR and alternative fuelsSolutions for improved fuel economy
Dr. Terry Alger
November, 2007
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• Emissions standards have been getting more strict on an approximately 4 year cycle– HD standards are less strict, but getting tighter quickly – Light duty standards are already fairly strict, but there is
always potential for further reductions
• New concerns regarding “global climate change” and energy security have resulted in a renewed focus on fuel economy
• Customers are concerned about fuel consumption– Cost of gasoline is getting higher– Social aspects– CO2 regulation increasing
• High mileage vehicles offer a significant marketing opportunity
Motivation and Market Forces
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The Route to High Efficiency• Gasoline engines have the potential to be intrinsically more
efficient than diesel engines– Otto cycle has significantly higher ideal efficiencies than Diesel cycle
• In the “real world” gasoline engines suffer from some drawbacks
– Pumping losses• Emissions standards require TWC and a fixed A/F ratio – throttle is
required– Knock
• Limits compression ratio• Spark retard to combat knock severely reduces efficiency• Spark retard also increases exhaust temperatures
– Requires overfuelling– Engine cannot meet emissions at high load
• 2 routes to high efficiency:1. Downsize and boost at “normal compression ratio”2. Increase compression ratio and maintain or increase displacement
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A Solution for High Efficiency• Reduce or eliminate pumping
losses– Use cam phasing and/or hot
EGR at low load to increase internal residual
– Reduce engine displacement• Requires higher manifold
pressures for the same torque as the larger engine
• Increase compression ratio– Better thermal efficiency
• Boost to increase specific power– Overcomes small displacement– Improved marginal efficiencies
Ignition and flame propagation
difficult
Increased exhaust
temperatures require
overfuelling
KNOCK
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Overcoming Obstacles to High Efficiency• Advanced ignition systems
– Improve EGR tolerance– Increase knock tolerance
• Cooled EGR– Reduces knock
• Combustion phasing improves for high efficiency• Enables high CR and/or loads
– Reduces exhaust temperatures• More effective dilution than overfuelling• Combustion phasing improvement also helps with combustion
temperatures
• Change the chemical composition of the charge– H2 reformer– Alternative fuels
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Improving ignitability
Fine Iridium ElectrodeHT lossesRequired breakdown voltage
Large GapHT lossesQuenching
Required breakdown voltageFlow CouplingEMI
Higher Energy LevelsFlame kernel volumeSecondary currents
Proportional heat lossesSpark “blow-out”Durability(?)
Long Duration / Multiple SparksProbability of ignitionFlow couplingInitial flame volume
Knock tendencyEffect of cylinder pressure
on spark event
Top systems to date:
• Dual fine electrode spark plugs
• High energy, long duration spark systems
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Ignition System Improvement at Low Loads• Very low loads present
challenges to ignition with EGR– High levels of in-
cylinder residual– Relatively cooler
temperatures• Residual• “Hot” EGR• Engine surfaces
• MS System V2.1 has the best EGR tolerance– Best low load EGR
tolerance– Burn duration and
stability very good 0 5 10 15 200
2
4
6
8
EGR [%]
Stock System MS system V1.0 MS System V1.1
MS System V2.0 MS System V2.1
CoV
IMEP
[%]
2000 rpm / 2 bar bmep
2.4-L engine @ 9:1 CR
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Burn rate improvement with new ignition• MS system V2.1 results
in faster burn rates at high and low load– EGR tolerance improves– Emissions and FE
improve– Knock resistance
improves• Level of improvement
would be greater for engines with higher levels of bulk motion– MS V2.1 may be able to
tolerate higher levels of bulk motion than other systems
40
50
60
70
80
90
0 5 10 15 20 25405060708090
3500 rpm / 9.6 bar bmep
0-50
% M
FB D
urat
ion
[deg
]
EGR [Vol %]
0-50
% M
FB D
urat
ion
[deg
]
Stock System MS system V1.0 MS system V2.0 MS system V1.1 MS system V2.1
2000 rpm / 2 bar bmep
2.4-L engine @ 9:1 CR
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High Load Performance• Ignition challenges at high
load are different– Spark blow out /
suppression– EMI– Pre-ignition
• MS V2.1 improves EGR tolerance at high load and reduces knock tendency– 20% EGR suppresses
knock – Engine runs at or near
MBT timing• Burn rate improvement
significant• WOT fuel economy good
despite low CR
1500 2000 2500 3000 3500 40006
8
10
12
14
16 220
230
240
250
BM
EP [b
ar]
Engine Speed [rpm]
20% EGRPeak loads limited by turbocharger
Stock System MS system V1.0 MS System V1.1
MS System V2.0 MS System V2.1
BSF
C [g
/kW
h]
2.4-L engine @ 9:1 CR
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Improving ignition (non-igniter hardware)
• Many other parameters can be adjusted to improve ignition– Increase coolant temperature
• Hotter temperatures at compression• EGR mitigates knock
– Increase compression ratio• Higher compression temperatures• EGR reduces knock• Also improves efficiency
• Change composition of the intake charge– H2 supplementation has significant potential
• Only small amounts required for benefit (SAE paper 2007-01-0475)
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H2 Amount and the Effect on Engine Stability• Very small amount of H2
necessary to stabilize engine– < 1 mg of H2 stabilizes
engine at most test conditions (~ 5% of gasoline mass)
– Benefits of H2 addition rapidly fall off at levels > 0.2 % by volume
• At high CR and high load, knock limits the benefit until high H2 levels reached
• H2 appears to improve stability through increased burn rates and more complete combustion
0.0 0.2 0.4 0.6 0.8 1.00
2
4
6
8
10
CoV
of i
mep
[%]
Volume % H2
11:1 CR; 3.1 bar imep (22% EGR) 11:1 CR; 5.5 bar imep (28% EGR) 14:1 CR; 3.1 bar imep (32% EGR) 14:1 CR; 5.5 bar imep (26% EGR)
Results from SAE Paper 2007-01-0475
0.75-L engine
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The Influence of H2 on Turbulent Burn Rate• Effect of H2 seen in 10-
90% MFB duration and spark advance– Biggest impact seen
with initial H2 addition
• H2 improves apparent flame speeds– Larger flammability
limits– Higher laminar burning
velocities– Reduced quench
distances
0.0 0.2 0.4 0.6 0.8 1.020
30
40
50
60
70
80
90 Spark Advance [deg bTDC] 10-90% MFB Duration [deg]
H2 [vol %]
3.1 bar imep, 11:1 CR, 22% EGR
Results from SAE Paper 2007-01-0475
0.75-L engine
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The Influence of H2 on Emissions• HC emissions reduced
considerably– H2 addition promotes
post-flame consumption of HC
– Crevice emissions reduced due to shorter wall quench distances
– Flame propagation improved due to improved flammability limits
• NOx emissions increase– Hotter flame temperatures
due to faster flame speeds– Still significantly reduced
from no EGR case
0.0 0.2 0.4 0.6 0.8 1.040
60
80
100
120
140
160
Perc
ent c
hang
e (0
% H
2 = 1
00%
) ISHC ISNO
H2 [vol %]
3.1 bar imep, 11:1 CR, 22% EGR
Results from SAE Paper 2007-01-0475
0.75-L engine
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The Influence of H2 on EGR Tolerance• H2 constant at 1% by
volume• EGR tolerance increased
significantly– Benefit largest at low load
• EGR tolerance lower without H2 at this load
• Engine still very knock limited at high loads and high CR
• No boost – WOT condition stops EGR sweep
• Best results in multi-cylinder engine found at 40-50% EGR
20 25 30 35 40 45 50 55 600
2
4
6
8
10
CoV
of I
MEP
[%]
EGR %
11:1 CR; 3.1 bar imep 14:1 CR; 3.1 bar imep 11:1 CR; 5.5 bar imep 14:1 CR; 5.5 bar imep
EGR Limited by WOT
Stability Limit
Results from SAE Paper 2007-01-0475
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Ignition Improvement Options• Advanced igniter and coil designs pay big
dividend– Best MS system yielded a 100%
improvement in EGR tolerance• Changing fuel composition also works well
– Small amounts of H2 can significantly improve performance
• Emissions and fuel consumption are reduced• Engine stability improves
– Low mass of H2 makes reformer technology more easily packaged and less energy consumptive
– Ethanol will improve knock tolerance• Other techniques are proving to have some
benefits– Increasing manifold temperatures works well– High CR and coolant temperatures also help
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Cooled EGR for Knock Reduction• Boosted gasoline engines
are knock limited above 12-14 bar bmep (or less)– Significant spark retard
required to prevent knock– Excess fuel required to
reduce exhaust temperatures• Cooled EGR can reduce
knock tendency – Restore optimal combustion
phasing– Allows stoichiometric
combustion• Enables aggressive
downsizing ( > 25%) for US market
0 5 10 15 20 25-30
-20
-10
0
10
20
30
40
240
250
260
270
280
290
300
3100 5 10 15 20 25
-15
-10
-5
0
5
10
15
20
240
250
260
270
280
290
300
310 Spark Advance CA 50% MFB BSFC [g/kWh]
Deg
rees
afte
r TD
C
EGR [%]
Desired location of CA 50% MFB for MBT
Low speed / high load conditions2.4-L engine @ 10.5:1 CR
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Cooled EGR for Reduced Exhaust Temperatures• All EGR conditions run at
φ = 1.0• EGR reduces high load
exhaust temperatures significantly– Cost savings potential in
• Turbine materials• Exhaust valve and seat
materials• Catalyst substrate• Warranty exposure
– Also has the potential to reduce under-hood temperatures
• Less load on heat exchangers
• Increased ability to run at high loads in drive cycle– Emssions compliance at
high load realized– Greater downsizing
potential
0 5 10 15 20
600
700
800
900
1000
1100 2000 rpm / 14 bar bmep 2000 rpm / 18 bar bmep 4000 rpm / 18 bar bmep 5500 rpm / 15 bar bmep
Pre-
Turb
ine
Tem
pera
ture
[deg
C]
EGR [%]1.6-L GDI engine (10.5:1 CR)
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Cooled EGR at High Speed / High Load
• Fuel consumption reduced by 5-20% due to elimination of enrichment (depending on engine power and enrichment levels)• Exhaust temperature reduced by ~100 deg C with EGR addition• Emissions reduced significantly
→ High load / WOT may now be a potential drive-cycle operating condition for a LD automotive application
0 5 10 15 20 25
700
720
740
760
780
800
220
225
230
235
240
245
Exha
ust T
empe
ratu
re [d
eg C
]
EGR [%]
Temperature @ Phi = 1.0 BSFC @ Phi =1.0 Temperature @ Phi = 1.05 BSFC @ Phi = 1.05
BSF
C [g
/kW
h]
BSCO BSNO BSHC0
10
20
30
40
50
BS
emis
sion
s [g
/kW
h]
6%
-65%
-77%
2.4-L engine @ 10.5:1 CR
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Cooled EGR at Low Speed / High Loads• At low speeds and high
loads, enrichment is not typically an issue– Despite high levels of
spark retard, exhaust temperatures are not excessive
– Poor efficiency is due solely to spark retard due to knock
• EGR addition reduces knock– Big change in BSFC– BSCO and BSNO are
reduced significantly0 5 10 15 20 25 30 35
0
5
10
15
210
220
230
240
250
EGR [%]
BSFC [g/kWh] BSCO [g/kwH] BSNO [g/kWh] BSHC [g/kWh]
2.4-L engine @ 9.5:1 CR
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Downsizing Potential• BMEP values based on a 3 L
engine (i.e. 11 bar bmep in a 3 L = 14 bar in the 2.4 L)
• Engine calibration will require a continuum of EGR temperatures for optimal performance
• Low speed, high BMEP operation enabled by knock reduction from EGR– Shift vehicle operation window– Diesel-like torque curve
• Future emissions standards will require compliance at high loads– Enrichment region will be
eliminated or very limited
Potential BSFC improvement due to downsizing
1 3 4 5 6 7 8
5
10
15
20
25 Hot EGR Cold EGR
% d
ecre
ase
in B
SFC
Test Point
Test Point Conditions1 4400 rpm / 11 bar bmep3 800 rpm / 7 bar bmep4 1500 rpm / 1 bar bmep5 1600 rpm / 2.4 bar bmep6 2000 rpm / 2 bar bmep7 2000 rpm / 5 bar bmep8 3500 rpm / 7.5 bar bmep
Downsizing Goal:Run FTP at > 10 bar bmepIdle @ 2-3 bar imep or more
10.5:1 CR
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Cooled EGR and High CR Operation
1500 2000 2500 3000 3500 40000
2
4
6
8
10
200
210
220
230
240
25035% BTE
BM
EP [b
ar]
Engine Speed [rpm]
39% BTE
BSFC
[g/kWh]
Peak load limited by NA operation
• Friction losses increased significantly– Problem worse at low loads
and high speeds• EGR reduces knock
tendency enough to get near full load– If external boost is applied,
10-11 bar is likely
2.4-L engine @ 14:1 CR
Full Load Curve
6 8 10 12 14 16 180
20
40
60
80
0
2
4
6
8
10
10-9
0% M
FBD
urat
ion
[deg
]
EGR %
10:1 CR 14:1 CR
CO
V im
ep [%
] • High CR helps with EGR
tolerance at low loads– Hotter temperatures
improve stability and flame speed
– Less internal residual
1500 rpm / 1 bar bmep
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When do we use hot EGR?
02468
20
25
30
5 10 15 20 2505
1015202530
BSCO [g/kWh]
BSHC [g/kWh]
BSNO [g/kWh]
EGR [%]
Incomplete combustion loss [kW]
Heat Lost to Exhaust [kW]
CoV imep [%]
2500 rpm / 6.7 bar bmepHEGR CEGR
• Hot / uncooled EGR is beneficial as long as knock does not occur– Higher MAT increases EGR
tolerance– Higher MAT helps charge
preparation • CO emissions reduced over
cooled EGR– Higher MAT promotes more
complete combustion– Pre-heating intake air increases
cycle efficiencies• NO emissions increase slightly
– Still below baseline / 0% EGR levels
• Substantial CO reductions– WHY?
• Exact cutoffs between when to use cooled or uncooled EGR TBD on engine-by-engine basis
2.4-L engine @ 9.0:1 CR
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CO reductions with EGR• CO emissions are lower with
EGR in almost all applications• With H-EGR, part of the
reduction in CO emissions may come from improved vaporization / charge preparation
• At high loads, MAT is controlled by aftercooler
– No temperature differences between EGR condition and baseline conditions
– CO emissions still decrease• Simulations using CEA code
indicate that lower temperatures due to dilution result in less CO emissions
– Occurs with several diluent types– Very strong temperature effect– Lower temperatures reduce
dissociation• Unanticipated benefit of EGR use
1900 2000 2100 2200 2300 24000
40
80
120
160
200
2200 2400 2600 2800 30000
10
20
30
40
50
T0 = 500 K T0 = 1000 KT0 = 1500 K
CO
2 / C
O ra
tio
Flame Temperature [K]
Diluent: N2 (10% by volume)T0 = 300 K
Flame Temperature [K]
CO
2 / C
O ra
tio
N2 diluent CO2 diluent
25% dilution15% dilution
10% dilution
0% dilution
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The Path to Fuel Economy: High CR versus High Load?• Question: What is the most effective way to
improve drive cycle efficiencies?• High CR
– Offers theoretical advantages in thermodynamic cycle efficiency
– High load becomes difficult• BSFC penalty due to spark retard is high
– Low load performance usually improved– May be best for NA / low boost applications
14 16 18 20 22 24274
276
278
280
282
284
286
288
290
292
BSF
C [g
/kW
h]
Spark Advance [deg bTDC]
2800 rpm15 bar bmep0% EGRE50 Fuel2.0-L engine11:1 CR
MBT timing
0 2 4 6 8 10 12 14 16 18 2005
1015202530
Pumping losses [% of BMEP] Friction Losses [% of BMEP] Location of 50% MFB [deg]
BMEP [bar]
220240260280300320340360
BSF
C [g
/kW
h]
2000 rpm10%<EGR<20%
• High Load– Low CR (10<CR<12) with
radical downsizing– Allows MBT timing at very high
loads– Marginal efficiencies become
very high• Friction and pumping as a % of
fuel energy → 0– Reduces or eliminates low
BMEP operation
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Cooled EGR• Cooled EGR improves fuel economy
– Knock reduction leads to improved combustion phasing• Reduced fuel consumption• Reduced exhaust temperatures
– Diluent effect of EGR reduces exhaust temperatures• Reduces requirement for overfuelling• Engine becomes emission compliant over entire performance
map
• Cooled EGR helps with emissions– CO and NO emissions reduced with lower combustion
temperatures– Ability to run stoichiometric over full performance map
makes engine fully emissions compliant • Cooled EGR with moderate compression ratio enables
radical downsizing (> 40%)– Efficiency benefits of EGR + Boost outweigh the benefits of
very high compression ratio
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Alternative Fuels• HEDGE and ethanol
– EGR can further improve ethanol operation
• Further increase knock resistance• Reduce pumping losses• Hot EGR can increase MAT to
help with fuel preparation issues– Improved ignition system can
benefit ethanol operation • CS benefits• With or without EGR
• Limited HEDGE technology can enable more efficient flex-fuel vehicles– SwRI has applied for a patent
under the HEDGE program– Enable engine optimization for
E100 / E85 fuel – Protect for E0 operation with EGR
• Will also work for other alternative fuels
0
5
10
15
20
25
30
0 20 40 60 80 100
Ethanol Percetnage in Fuel
EGR
Per
cent
age
in E
ngin
e
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15.9 15.917.2
19.3
0.0
5.0
10.0
15.0
20.0
25.0
NO EGR EGR
Dilution Case
BM
EP
(bar
)
92RON
92RON+H2
100RON
E50
E85
BMEP Limit Comparison (CR=11:1, Ф=1 )
• Exceeded BMEP target with E50 and E85 without EGR
• Exceeded BMEP target with 100 RON + EGR
• BMEP target NOT met with 92 RON due to engine knock and combustion stability limits
• BMEP target was met with 92 RON + EGR + H2 (60% increase)
• EGR alone extended knock limit by ~20% for gasoline fuels
Kno
ck &
PTT
Kno
ck &
PTT
Kno
ck (
MB
T)
Kno
ck &
PTT
Pea
k C
ylin
der P
ress
ure
(MB
T)
Kno
ck &
CoV
IME
P
Max
MAP
& K
nock
& C
oV
Max
MA
P &
Kno
ck (M
BT)
Target From Baseline (CR=9:1)
EGR ~ 21%
2800RPM
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BTE Comparison (CR=11:1, Ф=1 )
• BTE for ethanol blends exceeded 38%
• 100 RON + EGR achieved target BMEP at 37.3% BTE
• 92 RON + EGR + H2achieved ~30% BTE
– Lower BTE due to retarded spark timing and losses due to reforming the fuel
• 92 RON + EGR operated at > 35%, but not at target BMEP
– Enrichment may be used to increase knock limited BMEP
29.6
37.338.3 39.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
NO EGR EGRDilution Case
BTE
(%)
92RON
92RON+H2
100RON
E50
E85
2800RPM
NOTE:
The amount of fuel required to make the H2 was accounted for in BTE and BSFC comparisons –
Assumed an ideal fuel reformer
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Comparison to Baseline
02468
1012141618
BM
EP
(bar
)
E85E85+EGR100RON+EGR92RON+EGR+H292RON Cr=9:1
0.80
1.00
1.20
1.40
1.60
0 1000 2000 3000 4000 5000 6000 7000
Engine Speed (rpm)
Equ
ival
ence
Rat
io
• Baseline Data– CR=9:1– Turbocharged – WOT– To meet target BMEP
• Spark retard for knock• Ф > 1 due to PTT limit
• Test Data– CR=11:1– Supercharged – WOT– To meet target BMEP
• Spark retard for knock • Ф held to 1
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Comparison to Baseline
• E85 + EGR was 9% higher than baseline even though the LHV of E85 was 25% lower than gasoline
• 92RON + EGR + H2 improved fuel consumption by 8%
• 100RON + EGR improved fuel consumption by 19%
• Fuel consumption difference between 100RON and E85 was proportional to difference in LHV
200220240260280300320340360380
0 1000 2000 3000 4000 5000 6000 7000
Engine Speed (rpm)
cBS
FC (g
/kW
-hr)
E85 E85+EGR100RON+EGR 92RON+EGR+H292RON Cr=9:1
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Result with Ethanol and EGR
• Test engine could operate as an E85 flex fuel engine with CR = 11:1– Premium required EGR to meet target load– Regular required EGR and H2 addition to meet target load
• EGR improved fuel consumption and emissions with ethanol blended fuels
• Increasing CR and employing EGR improved engine performance and emissions compared to base engine operating on gasoline– NOX and CO were significantly reduced – Full load fuel consumption with regular gasoline was estimated to be
8% lower with EGR and H2
– Full load fuel consumption was only 9% higher with E85 (EGR, CR=11:1) than base engine (No EGR, CR=9:1) despite 25% lower LHV
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EGR Systems
PM Traps
High EGR,NOx Aftertreatment
Turbocharging
Intercooling
High PressureInjection
ElectronicFuelInjection
U.S. Heavy-Duty On-Road –Emissions Regulations Increasingly Difficult to Meet
ImprovedCombustion &RetardedTiming
Emissions Regulation History and Technology Solutions
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Engine, Emissions and Vehicle Research DivisionSouthwest Research Institute
Engine, Emissions and Vehicle Research DivisionEngine, Emissions and Vehicle Research DivisionSouthwest Research InstituteSouthwest Research Institute
Emissions Regulation History and Technology Solutions
U.S. Light-DutyEmissions Regulations
Toughest Anywhere
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Include Fuel Economy and the Problem is Clear http://www.sanantoniogasprices.com/retail_price_chart.aspx
Fuel price is increasing and highly volatile
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CO2 Review
• Europe CO2 Regulations– Europe sets CO2 goals for near
future• 120 g/km maximum CO2
• U.S. Supreme Court ruling– U.S. EPA should consider CO2– Likely that CO2 regulation will
occur in U.S.– U.S. President reveals plan to
pursue CO2 reduction• Asks EPA and DOE to work together
for CO2 reduction
From SwRI Consulting Service Report:
Climate change awareness is intensifying in the US. The recent Supreme Court decision ordering the EPA to take action to reduce GHG emissions from vehicles lags state actions which are already moving ahead with their own low-carbon vehicle rules, potentially leading to a GHG policy “mess”. To avoid that, the US president ordered EPA, the Department of Transportation, the Department of Energy and the Department of Agriculture to propose and finalize new regulations by the end of next year that would respond to the Supreme Court order. As a starting point for such new regulation, the president proposed a 20% cut in gasoline consumption by 2017, which would force 35 billion gallons of renewable and other fuels into the US motor fuel pool by 2017. According to an environmental law specialist, the “mess” involves regulation, litigation, and Congress trying to figure out GHG legislation and how the transportation sector fits in. According to him, the ideal solution would be for Congress to take action, eliminating states from the equation. (WRFT 23-05-07)