Effects of Methyl Ester BiodieselEster Biodiesel Blends on NOx
EmissionsSAE 2008-01-0078
Wayne Eckerle Edward Lyford PikeWayne Eckerle, Edward Lyford-Pike, Donald Stanton, Leon Lapointe, Shawn Whitacre, John Wall
MSTRS Meeting May 8, 2008
BackgroundBackground
Impact of methyl ester biodiesel on regulated p y gemissions:
Reduces particulate matterpReduces unburned hydrocarbonsEffects on NOx vary in magnitude and y geven direction across multiple studies
Thi t d f d B20 f d t NOThis study focused on B20 for adequate NOx response
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Cause of Change in NOx Emissions Due to B20
Fundamental combustion effects due to fuel chemistry and fluid dynamicsfuel chemistry and fluid dynamics
Generally engine independent
Interaction of the lower specific energy content of the biodiesel with the
i lengine control systemInteraction is engine specific
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Approach
Gather an accurate experimental data set using a single cylinder engine operating on two commercial diesel fuels and y g gB20 blends of those fuels.
Calibrate the KIVA combustion CFD modelCalibrate the KIVA combustion CFD model.
Investigate the fundamental combustion impact of B20. es ga e e u da e a co bus o pac o 0
Calculate the engine controls impact of B20.
Calculate the net impact of B20 on NOx over several key duty cycles
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cycles.
Test Fuels
CN44 DF2 – higher aromaticsCN48 CN44 + 20% biodiesel
CN51 DF2 – lower aromaticsCN52 CN51 20% bi di lCN52 CN51 + 20% biodiesel
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Fuel PropertiesAromatics Sulfur Specific Viscosity Cetane p y
(%) ppm Gravity cSt NoMethod ASTM D5186 D5453 D445 D613High Aromatics Fuel - DF2 (CN44) 31.4 8 0.84 2.25 44.4Low Aromatics Fuel - DF2 (CN51) 8.4 0 0.83 2.41 51( )B20/High Aromatics - B20 (CN48) 25.1 6 0.85 2.54 48B20/Low Aromatics - B20 (CN52) 6.7 0 0.84 2.63 51.5B100 0 0 0.89 4.14 51.6
• Cetane number is generally correlated with aromatic content.• Higher aromatic fuels generally have lower cetane numbersHigher aromatic fuels generally have lower cetane numbers.
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Single Cylinder Engine Test SetupSingle Cylinder Engine Test Setup
CoV of Fuel Specific NOx<0.5%
X X X X X X X X X X
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Combustion ModelingCombustion Modeling
KIVA3-RIF CFD CodeEnables use of extensive biodiesel kinetics mechanismsmechanisms Methyl butanoate selected for biodiesel mechanismMixture of n-decane and α-methylnaphthelene for DF2252 non-steady state species Surrogate fuel mixtures selected to match experimental autoignition characteristics of the blendsautoignition characteristics of the blends
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Engine Operating Conditions Used forEngine Operating Conditions Used for Single Cylinder Testing
ISB 6.7L
600
700
800
350 hp torque curve350 hp torque curve
600
700
800
350 hp torque curve350 hp torque curveDetailed Analysis
400
500
600
e [ f
t-lb
] Diffusion Combustion
B75 C75400
500
600
e [ f
t-lb
] Diffusion Combustion
B75 C75
y
200
300
400
Torq
ue
Mode 4
C50
200
300
400
Torq
ue
Mode 4
C50
0
100
700 1200 1700 2200 2700 3200
Partially Premixed
Mode 4
0
100
700 1200 1700 2200 2700 3200
Partially Premixed
Mode 4
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700 1200 1700 2200 2700 3200
Engine Speed [ rpm ] 700 1200 1700 2200 2700 3200
Engine Speed [ rpm ]
Fundamental Combustion Effects
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NOx ~ Temperature
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Diesel Combustion
• Initial fuel injected into hot combustion airInitial fuel injected into hot combustion air• Fuel and air mix before combustion starts• Initial combustion of pre-mixed fuel
(lower temperature lower NOx)(lower temperature lower NOx)• Continued mixing and diffusion combustion
as the rest of the fuel is injected
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(higher temperature higher NOx)
Diesel Combustion
1 Premixed depends on ignition1. Premixed – depends on ignition delay
2. Diffusion controlled – dominant at high load
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Fuel Effects on Combustion / NOxFuel Effects on Combustion / NOx
Premixed fraction / Ignition delay is driven by cetane number (aromatics)
Lower cetane longer ignition delayLower cetane longer ignition delay more premixing lower NOxNot a linear effect – higher cetane fuels show less differenceMore important at lighter loads (a greater fraction of the fuel burns premixed)fraction of the fuel burns premixed)
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Combustion at Mode 4 (Light Load)Combustion at Mode 4 (Light Load)
375375
300
325
350 Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)300
325
350 Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
225
250
275
300
ust N
Ox
(PPM
) ( )( )( )( )
225
250
275
300
ust N
Ox
(PPM
) ( )( )( )( )( )( )( )( )
B20 effect
175
200
225
Raw
Exh
a
S lid Li E i D tS lid Li E i D t175
200
225
Raw
Exh
a
S lid Li E i D tS lid Li E i D t
100
125
150 Solid Lines – Engine DataDashed Lines – KIVA DataSolid Lines – Engine DataDashed Lines – KIVA Data
Solid Lines – Engine DataDashed Lines – KIVA DataSolid Lines – Engine DataDashed Lines – KIVA Data
Solid Lines – Engine DataDashed Lines – KIVA Data
100
125
150 Solid Lines – Engine DataDashed Lines – KIVA DataSolid Lines – Engine DataDashed Lines – KIVA Data
Solid Lines – Engine DataDashed Lines – KIVA DataSolid Lines – Engine DataDashed Lines – KIVA Data
Solid Lines – Engine DataDashed Lines – KIVA Data
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16.3% 16.5% 16.8% 17.0% 17.3% 17.5% 17.8% 18.0%Intake O2 (Vol %)Intake O2 Concentration (%)Intake O2 Concentration (%)
16.3% 16.5% 16.8% 17.0% 17.3% 17.5% 17.8% 18.0%Intake O2 (Vol %)Intake O2 Concentration (%)Intake O2 Concentration (%)
Effect of Biodiesel on Ignition DelayEffect of Biodiesel on Ignition Delay
0.20.2
0.15
deg)
EnginePredictionEnginePrediction
EnginePredictionEnginePrediction
0.15
deg)
EnginePredictionEnginePrediction
EnginePredictionEnginePrediction
0.1
se R
ate
(Btu
/d B20 (CN 48)
Diesel Fuel (CN 44)0.1
se R
ate
(Btu
/d B20 (CN 48)
Diesel Fuel (CN 44)
0.05
nt H
eat R
elea
s
0.05
nt H
eat R
elea
s
00 5 10 15 20 25
App
are
00 5 10 15 20 25
App
are
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-0.05
Crank Angle (deg atdc)-0.05
Crank Angle (deg atdc)
C b ti Eff t t L L dCombustion Effect at Low Load
Low cetane longer ignition delay more premixingLow cetane longer ignition delay more premixing lower NOx
B20 blend has higher cetane number than its base fuel
B20 h l ff NO l l d i h lB20 has a larger effect on NOx at low load with low cetane fuels
B20 causes ~ 5% increase in NOx with lower cetane fuel on average across pre-mixed combustion zone
Small effect for higher cetane fuels
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Small effect for higher cetane fuels
Fuel Effects on Combustion / NOxFuel Effects on Combustion / NOx
NOx from Diffusion Controlled Combustionis driven by details of fuel chemistry
Higher aromatics higher TD bl b d i th l t bi di lDouble bonds in methyl-ester biodiesel higher TMono and Polyalkylbenzene reactivity isMono and Polyalkylbenzene reactivity is affected by methyl esters
• Effect is larger for high aromatic fuels• Recent understanding
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Diffusion Flame CombustionC75 Condition (High Load)
160
Solid Lines Engine Data
160
Solid Lines Engine DataSolid Lines Engine Data
150
155
M)
Solid Lines – Engine DataDashed Lines – KIVA Data
Solid Lines – Engine DataDashed Lines – KIVA Data
150
155
M)
Solid Lines – Engine DataDashed Lines – KIVA Data
Solid Lines – Engine DataDashed Lines – KIVA DataSolid Lines – Engine DataDashed Lines – KIVA Data
Solid Lines – Engine DataDashed Lines – KIVA Data
B20 Effect
140
145
haus
t N
Ox
(PPM
140
145
haus
t N
Ox
(PPM
Commercial diesel fuel NOx range
B20 Effect
130
135
Raw
Ex
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
130
135
Raw
Ex
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
Low Cetane Diesel Fuel (CN44)Low Cetane B20 Blend (CN48)Hi Cetane Diesel Fuel (CN51)
fuel NOx range
120
125
17.3% 17.4% 17.5% 17.6% 17.7% 17.8%
Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
120
125
17.3% 17.4% 17.5% 17.6% 17.7% 17.8%
Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)Hi Cetane Diesel Fuel (CN51)Hi Cetane B20 Blend (CN52)
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Intake O 2 Concentration (%)Intake O 2 Concentration (%)
C b ti Eff t t Hi h L dCombustion Effect at High Load
Hi h ti di l f l d NOHigh aromatic diesel fuels produce more NOx
B20 blends have a small effect on NOx (1%)Competing chemical mechanisms offsetCompeting chemical mechanisms offset
Fundamental combustion effect of B20 on NOx at high load is less than the NOx difference measured gbetween commercially available fuels
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Summary of Fundamental Combustion Effects
Light load, lower cetane base fuel g ,B20 increased NOx ~ 5%
Everywhere else: little effect
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Interaction With Engine ControlsInteraction With Engine Controls
Controls effects are engine specific… so these observations and conclusions are for current Cummins electronicare for current Cummins electronic engines. With knowledge of controls calibration, similar calculations can be
d f imade for any engine.
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Typical Engine Control Structure
Bi di l L t tBiodiesel: Lower energy content More fuel for the same Torque Calibration changes
Torq
ueue
l Rat
e
Intake O2 ,Injection Timing, Fuel Pressure,
TFu Number of injections and Distribution
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Speed
Impact of Engine Controls on EGR atImpact of Engine Controls on EGR at High-Load Condition
14.2% EGR – B100 (CN 52)14.2% EGR – B100 (CN 52)
oad
(lb-ft
) 14.2% EGR – B100 (CN 52)14.2% EGR – B100 (CN 52)
oad
(lb-ft
)
15.8% EGR - B20 (CN 48)
16.2% EGR – DF2 (CN 44)
15.8% EGR - B20 (CN 48)
16.2% EGR – DF2 (CN 44)
alen
t Eng
ine
Lo 15.8% EGR - B20 (CN 48)
16.2% EGR – DF2 (CN 44)
15.8% EGR - B20 (CN 48)
16.2% EGR – DF2 (CN 44)
alen
t Eng
ine
Loet
DF2
–Eq
uiva
et D
F2 –
Equi
vaTa
rgTa
rg
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Engine Speed (rpm)Engine Speed (rpm)
Impact of Engine Controls at
% NOx Impact on B20 DF2 Units % NOx Impact on B20 DF2 Units
High-Load Condition
8.0↑19.118.7%Intake O2
ChangepNOx(CN 48)(CN 44)
8.0↑19.118.7%Intake O2
ChangepNOx(CN 48)(CN 44)
- 4.5↓3.03.5deg btdcMain SOI
↑2
- 4.5↓3.03.5deg btdcMain SOI
↑2
-1↓9.59.1mg/strokePost Quantity
1↑12801275barRail Pressure
-1↓9.59.1mg/strokePost Quantity
1↑12801275barRail Pressure
0─0.020.02mg/strokePilot Quantity
↓Quantity
0─0.020.02mg/strokePilot Quantity
↓Quantity
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0─156156oFIMT 0─156156oFIMT
Combined NOx Impact for High-LoadCombined NOx Impact for High Load Operating Point
Impact of B20 on NOx at Constant Calibration (Combustion) 1.0%Impact of B20 on NOx at Constant Calibration (Combustion) 1.0%
Impact of B20 on NOx due to Engine Calibration
Predicted Net NOx Increase
3.5%
4.5%
Impact of B20 on NOx due to Engine Calibration
Predicted Net NOx Increase
3.5%
4.5%
Engine Data:
DF2 (CN 44)
B20 (CN 48)
1.72 g/bhp-hr NOx
1 78 g/bhp hr NOx
Engine Data:
DF2 (CN 44)
B20 (CN 48)
1.72 g/bhp-hr NOx
1 78 g/bhp hr NOxB20 (CN 48)
Net NOx Increase
1.78 g/bhp-hr NOx
3.5%
B20 (CN 48)
Net NOx Increase
1.78 g/bhp-hr NOx
3.5%
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Combined NOx Impact for Low-Load Operating Pointp g
Impact of B20 on NOx at Constant Calibration (Combustion) 5.3%Impact of B20 on NOx at Constant Calibration (Combustion) 5.3%
Impact of B20 on NOx due to Engine Calibration
Predicted Net NOx Increase
-4.5%
0.8%
Impact of B20 on NOx due to Engine Calibration
Predicted Net NOx Increase
-4.5%
0.8%
Engine Data:
DF2 (CN 44)
B20 (CN 48)
2.42 g/bhp-hr NOx
2.45 g/bhp-hr NOx
Engine Data:
DF2 (CN 44)
B20 (CN 48)
2.42 g/bhp-hr NOx
2.45 g/bhp-hr NOx
Net NOx Increase 1.3%Net NOx Increase 1.3%
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Change in NOx Emissions with B20 BlendsChange in NOx Emissions with B20 Blends for Several Engine Duty Cycles
10
8
10
FTP
HWY55
4
6
e in
NO
x (%
)
UDDS 6k
0
2
0 0.5 1 1.5 2 2.5 3 3.5 4
Perc
ent C
hang
e
-4
-2
P
5.9L ISB Reference [20]5.9L ISB - KIVA10.8L ISM Reference [4]10.8L ISM - KIVA15L ISX KIVACSHVC
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-6
Normalized Cycle Fuel Consumption (kg/hr/L)
15L ISX - KIVA
Effect of Biodiesel Concentration on FTP NOx
DF2 DF2 ~ 5%
B50.5%
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Conclusions
Effect of B20 on NOx emissions is determined by fundamental combustion effects and interaction with engine controls. The experimentally observed “tailpipe NOX” effect is the sum of theexperimentally observed tailpipe NOX effect is the sum of the two.
Th ff f b i d i l NO lThe net effect of combustion and engine controls on NOx at low loads depends on the cetane number of the blends: 1% increase with low cetane to a 5% decrease with high cetane.
The net effect of B20 on combustion and engine controls on NOx at high loads is a 4-5% increase. This is mostly due to engine controls.
Competing and contingent effects described in this paper explain
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Competing and contingent effects described in this paper explain the variation seen in published test results.
Summary: The Effects of B20 on NOx Emissions
APPLICATION B20 EFFECT
COMBUSTION CALIBRATION NETCETANE LOAD COMBUSTION EFFECT
CALIBRATION EFFECT
NET EFFECT
Low Low ( + ) ( - ) 0Low Low ( + ) ( - ) 0
High Low 0 ( - ) ( - )
Low High 0 ( + ) ( + )
High High 0 ( + ) ( + )
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High High 0 ( + ) ( + )
Conclusions
Expect an increase in NOx emissions at high average cycle power with B20 (~5%).
Expect equal or lower NOx emissions at low average cycle power.
Expect a small in-use NOx effect in urban duty cycles where biodiesel is generally used today.
The difference in NOx between a B20 blend and its base diesel fuel is less that the difference in NOx between two commercial diesel fuels within the range of fuels in the market today.
The NOx effect on the FTP varies linearly with biodiesel concentration from 0 to 20%. At B5 the net NOx effect is negligible
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negligible.
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