Effects of Methyl Ester Biodiesel Ester Biodiesel Blends ... · Ester BiodieselEster Biodiesel...

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

2

Innovation You Can Depend On

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

3


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

4


cycles.

Test Fuels

CN44 DF2 – higher aromaticsCN48 CN44 + 20% biodiesel

CN51 DF2 – lower aromaticsCN52 CN51 20% bi di lCN52 CN51 + 20% biodiesel

5


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.

6


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

7


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

9


700 1200 1700 2200 2700 3200

Engine Speed [ rpm ] 700 1200 1700 2200 2700 3200

Engine Speed [ rpm ]

Fundamental Combustion Effects

10


NOx ~ Temperature

11


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

13


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)

14


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)300

325

350 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



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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


0.15

deg)



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

16


-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)



150

155

M)




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)




130

135

Raw

Ex









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%



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%



-4.5%

0.8%



-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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