Lawrence Livermore National Laboratory · Washington, DC. This presentation does not contain any proprietary, confidential or otherwise restricted information This work performed

Lawrence Livermore National Laboratory

Chemical Kinetic Research on HCCI & Diesel Fuels

William J. Pitz (PI), Charles K. Westbrook, Marco Mehl, Mani SarathyLawrence Livermore National Laboratory

May 10, 2011

DOE National Laboratory Advanced Combustion Engine R&D Merit Review and Peer Evaluation

Washington, DCThis presentation does not contain any proprietary, confidential or otherwise restricted information

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

Project ID # ACE013

LLNL-PRES-472814

2LLNL-PRES- 472814 2011 DOE Merit Review


Overview

• Project provides fundamental research to support DOE/ industry advanced engine projects

• Project directions and continuation are evaluated annually

Technical Barrier: Increases in engine efficiency and decreases in engine emissions are being inhibited by an inadequate ability to simulate in-cylinder combustion and emission formation processes• Chemical kinetic models for fuels are a

critical part of engine models Targets: Meeting the targets below relies

heavily on predictive engine models for optimization of engine design:• Fuel economy improvement of 25 and 40%

for gasoline/diesel by 2015• Increase heavy duty engine thermal

efficiency to 55% by 2018.• Attain 0.2 g/bhp-h NOx and 0.01 g/bhp-h PM

for heavy duty trucks by 2018

Project funded by DOE/VT:• FY10: 400K• FY11: 500K

Timeline

Budget

Barriers/Targets

• Project Lead: LLNL – W. J. Pitz (PI), C. K. Westbrook, M. Mehl, M. Sarathy

• Part of Advanced Engine Combustion (AEC) working group:

• – 15 Industrial partners: auto, engine & energy• – 5 National Labs & 2 Univ. Consortiums• Sandia: Provides HCCI Engine data for validation of

detailed chemical kinetic mechanisms• FACE Working group

Partners



Objectives and relevance to DOE objectives Objectives:

• Develop predictive chemical kinetic models for gasoline, diesel and next generation fuels so that simulations can be used to overcome technical barriers to low temperature combustion in engines and needed gains in engine efficiency and reductions in pollutant emissions

FY11 Objectives:• Develop a chemical kinetic mechanism for a new series of iso-alkanes

to help represent the iso-alkane chemical class in diesel fuel• To provide validation of the chemical kinetic mechanisms of the 2-

methyl alkane series• Develop chemical kinetic models to represent large aromatics in diesel

fuel• Develop improved gasoline surrogate fuels for HCCI engines• Development of very efficient software to reduce the size of detailed

chemical kinetic models for transportation fuels so that they can be effectively used in multidimensional engine simulation codes



Chemical kinetic milestones December, 2010

Validate the chemical kinetic mechanism of 2-methyl heptane• May, 2011

Development of a low and high temperature mechanisms for a new series of iso-alkanes for diesel fuel

• May, 2011 Test surrogate mixture models for gasoline by comparison to HCCI engine and RCM experiments

September, 2011Develop chemical kinetic model for a high molecular-weight aromatic

September, 2011Develop a functional group method to represent iso-alkanes in diesel fuel



Approach Develop chemical kinetic reaction models for each individual fuel component of

importance for fuel surrogates of gasoline, diesel, and next generation fuels

Combine mechanisms for representative fuel components to provide surrogate models for practical fuels• diesel fuel• gasoline (HCCI and/or SI engines)• Fischer-Tropsch derived fuels• Biodiesel, ethanol and other biofuels

Reduce mechanisms for use in CFD and multizone HCCI codes to improve the capability to simulate in-cylinder combustion and emission formation/destruction processes in engines

Use the resulting models to simulate practical applications in engines, including diesel, HCCI and spark-ignition, as needed

Iteratively improve models as needed for applications



0.00001

0.0001

0.001

0.01

0.1

1

0.7 1.0 1.3 1.6

φ=1

80atm

40 atm20 atm

P=10 atm

Igni

tion

Dela

y (s

)

Technical Accomplishment Summary

Development of chemical kinetic model for larger aromatics

Developed a functional-group kinetics modeling approach for iso-alkanes that greatly reduces the size of the mechanism

R-CH3 R-CH2CH2CH2CH2-R

Developed new approach for formulating gasoline surrogate mixtures for real gasoline fuels

Developed reduced mechanism for gasoline surrogate

C8 to C20 mechanism: 7900 species => 280 species

Validated the chemical kinetic mechanism of 2-methyl heptane

CH3+ +

(CH3)2CH-R

0.E+00

2.E-04

4.E-04

6.E-04

8.E-04

1.E-03

1.E-03

500 600 700 800 900 1000 1100 1200

Mol

e Fr

actio

n

Temperature (K)

Cool flame NTC region

Hot ignition

Fuel

C2H4

H2

1500 species

312 species



Iso-alkanes: The chemical kinetic mechanism for 2-methylalkanes has been submitted for publication

Includes all 2-methyl alkanes up to C20 which covers the entire distillation range for gasoline and diesel fuels

7,900 species

27,000 reactions

Built with the same reaction rate rules as our successful iso-octane and iso-cetane mechanisms

Recently submitted mechanism for publication: Sarathy, Westbrook, Mehl, Pitz, et al. (2011). "Comprehensive chemical kinetic modeling of the oxidation of C8 and larger n-alkanes and 2-methylalkanes." Combustion and Flame , Submitted.



Jet Stirred Reactors

• Idealized chemically reacting flow systems with/without simplified transport phenomenon

Non Premixed Flames

Premixed Laminar Flames

High pressure flow reactors

Engine Combustion

Combustion Parameters

Temperature

Pressure

Mixture fraction (air-fuel ratio)

Mixing of fuel and air

Validated iso-alkane mechanism using new experimental data from many different groups through collaborations

Shock tube

Electric ResistanceHeater

Evaporator

Fuel Inlet

Slide Table

Oxidizer Injector

Optical Access Ports

Sample ProbeWall Heaters

Rapid Compression Machines



Improved predictions for 2-methylhexane mechanism under engine conditions (RCM)

RCM experimental data:

Galway:Silke et al. Proc. Comb. Inst. (2005)

0

10

20

30

40

50

60

70

80

650 700 750 800 850 900 950

Igni

tion

Del

ay T

ime

(ms)

Temperature at End of Compression (K)

2-methylhexane, phi=1, 15 atm

Galway RCM data

new model

old model

Reaction rules were updated on the basis of our latest work on n-heptane leading to significant improvements



2-methylheptane model agrees well species profiles measured in a JSR at elevated pressure

Good prediction of low T and high T reactivity

Φ = 1, 10 atm, τ= 0.7s

Experiments: Dagaut et al. CNRS (2011)

0.E+00

2.E-04

4.E-04

6.E-04

8.E-04

1.E-03

1.E-03

500 600 700 800 900 1000 1100 1200

Mol

e Fr

actio

n

Temperature (K)

Cool flame NTC region

Hot ignition

Fuel

C2H4

H2

0.E+00

1.E-03

2.E-03

3.E-03

4.E-03

5.E-03

6.E-03

7.E-03

8.E-03

9.E-03

500 700 900 1100

Mol

e Fr

actio

n

Temperature (K)

H2O

CO

CO2

Jet stirred reactor (JSR)



Reduced chemical kinetic models for 2-methyl heptane well simulates extinction and ignition in a counterflow flame

To perform these reacting flow simulations: Mechanism reduced from 714 to151 species using directed relational graph method.(Collaboration with T. Lu at Univ. of Connecticut)

Experiments: K. Seshadri, Univ. of California, San Diego, 2011

1190

1200

1210

1220

1230

1240

1250

1260

1270

200 300 400 500 600 700

Tem

pera

ture

at A

utoi

gniti

on(K

)

Strain rate (s-1)

Fuel Stream: 2-methylheptane in N2Oxidizer Stream: airP = 1 atm

corrected T

uncorrected T

simulation0

0.1

0.2

0.3

0.4

0.5

0.6

50 150 250 350 450

Fuel

Mas

s Fr

actio

n

Strain rate at Extinction (s-1)

Fuel Stream: 2-methylheptane in N2Oxidizer Stream: airP = 1 atm

Extinction Ignition



Laminar flame speeds of n-octane and 2-methylheptane are well predicted by the model

0

10

20

30

40

50

60

0.6 0.8 1.0 1.2 1.4 1.6

Lam

inar

Fla

me

Spee

d, S

uo (c

m/s

)

Equivalence Ratio

n-octane/ 2-methylheptane in air, 353 K, 1atm

n-octane

2-methylheptane

Flame speeds of 2-methyl alkanes are slightly slower than n-alkanes’ ones: Chemical effect due to the formation of resonantly stabilized radicals by iso-alkanes

Flame speed measurements:Egolfopoulos et al. 2011 USC

Twin premixed counterflow flames



Chemical kinetic mechanism for larger aromatics

CO

CO2

H2O

The kinetic mechanism of the aromatics has an intrinsic hierarchical structure

A new module specific to C8 alkyl aromatics is now under development



p-Xylene mechanism well reproduces species profiles in jet stirred reactor

Experiments: Gail and DagautCombustion and Flame 2005

P = 1 atm, Ф = 1, τ = 0.1s

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

900 1000 1100 1200 1300 1400T [K]

O2

p-Xylene

CO

CH2O

CO2

1.E-06

1.E-05

1.E-04

1.E-03

900 1000 1100 1200 1300 1400T [K]

Benzaldehyde

Toluene

Benzene

Cyclopentadiene

Mol

e Fr

actio

n

Mol

e Fr

actio

n

Mol

e Fr

actio

n

T [K]

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

900 1000 1100 1200 1300 1400

H2

CH4

C2H4

C2H6

C2H4

Jet stirred reactor



10

100

1000

10000

100000

0.7 0.8 0.9 1

Ortho-, para- and ethyl-benzene models compare well to ignition delay times measured at pressure and temperatures relevant to engines

10 atm, fuel/air mixtures, φ=1

1000K/T

Igni

tion

Del

ay T

imes

[µs]

Ethylbenzene

Para-xyleneOrtho-xylene

Ignition delay times in a shock tube for aromatics

Shock tube experimental data: Shen and Oehlschlaeger, Combustion and Flame 2009



10

100

1000

10000

0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

TRF 25atm TRF 55atmRD387 25atm RD387 25atmRD387 55atm RD387 55atmSurrogate 25atm Surrogate 55atmPRF87 25atm PRF87 55atmIC8 55atm NC7 55atm

25 atm

55 atm

1000/T

Igni

tion

Del

ay T

imes

[μs]

Gasoline surrogates: New methodology for matching gasoline surrogate properties to real fuel

Experimental data for RD387 gasoline: Gauthier, Davidson, R.K. Hanson, 2004

Octane sensitivity is correlated to slope in the NTC region0 Sensitivity

Fuel (PRF87)8 Point Sensitivity Fuel

(RON+MON )/2=87



40 different gasoline surrogates were simulated to obtain key features of their ignition curves

1.0E-04

1.0E-03

1.0E-02

1.0E-01

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

Igni

tion

Del

ay T

imes

[s]

25 atm

1000K/T

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

1000K/T

Igni

tion

Del

ay T

imes

[s]

55 atm

Key feature of their ignition curves were correlated with their octane index (OI) and sensitivity

The slope in the NTC region is found to be proportional to the sensitivity while the ignition delay time at a specified T correlates with the OI

T=850 K

Experimental data: Personal communication and N.Morgan et al. Comb. & Flame

slope



Octane index correlates with ignition delay time and octane sensitivity correlates with slope in the NTC

y = 67.95x3 + 422.17x2 + 903.17x + 753.93R² = 0.99

0

20

40

60

80

100

120

140

-3.5 -3 -2.5 -2 -1.5 -1

PRFs

Ignition Delay Times [Log(1/s)]

OI

b)

Octane Index vs. Ignition Delay time @ 850K

Experimental data: Personal communication and N.Morgan et al. Comb. & Flame

Correlated parameters of octane rating with characteristics of ignition curve for 40 different surrogates

25 atmy = -0.60x2 + 2.64x + 8.86

R² = 0.79-2

0

2

4

6

8

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12

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16

-3 -2 -1 0 1 2 3 4

PRFs

Higher unsaturated content

Slope

Sens

itiv

ity

a)

Sensitivity vs. Slope

25 atm



Gasoline surrogate mechanism has been reduced for use in engine simulations

0.00001

0.0001

0.001

0.01

0.1

1

0.7 1.0 1.3 1.6

φ=1

80atm

40 atm20 atm

P=10 atm

Igni

tion

Dela

y (s

)

0.00001

0.0001

0.001

0.01

0.1

1

0.7 1.0 1.3 1.6

80 atm40 atm20 atm

P=10 atmφ=0.3

Ig

nitio

n De

lay

(s)

1000K/T1000K/T

Collaboration with J.Y. Chen, U. C. Berkeley

Reduction: 1500 species to 312 species

Comparison of ignition delay times for detailed and reduced mechanism:

Solid line: full mechanismSymbols: reduced mechanism



Reduced gasoline surrogate mechanism has also been validated against experimental flame speed data for gasoline

303540455055606570

0.6 0.8 1 1.2 1.4

0

5

10

15

20

25

30

35

0.6 0.8 1 1.2 1.4

φ φ

Flam

e Sp

eed

[cm

/s]

100°C

50°C

75°C

25 atm

10 atm

15 atm20 atm

1 atm

Experimental data: Jerzembeck & Peters SAE 2007Experimental data: Tian et al. Energy & Fuels 2010

Prediction of flame speed important for spark ignition engine simulations

Unburned gas temperature: 373K

Unburned gas temperature:



We have developed a novel functional group approach that greatly reduces the size of chemical kinetic mechanisms

2 + 3.5

C10H22 (Diesel Surrogate):

Proposed Approach:

250 Species 1400 Reactions

Mol

e co

ncen

tratio

n

Temperature [K]

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

700 800 900 1000 1100 1200

O2

CH4

C2H4

CO2CO

Traditional Approach:


JSR

Traditional Approach:

7900 Species 27000 ReactionsProposed Approach:


Detailed mechanism Functional group approach

Experimental data:10 atm, φ=1, 0.5s,

0.1% n-decaneJet Stirred ReactorDagaut et. al. 1994

C8 to C20 iso-alkanes:



Functional group approach has been successfully extended to 2-methylalkanes and validated in a JSR (2- methyl heptane)

0.00E+00

2.00E-03

4.00E-03

6.00E-03

8.00E-03

1.00E-02

1.20E-02

500 600 700 800 900 1000 1100 1200

H2O

CO

CO2

0.00E+00

2.00E-04

4.00E-04

6.00E-04

8.00E-04

1.00E-03

1.20E-03

500 600 700 800 900 1000 1100 1200

CH4

C2H4

H2

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

3.00E-04

3.50E-04

500 600 700 800 900 1000 1100 1200

CH2O

C3H6

C2H2

0.00E+00

1.00E-05

2.00E-05

3.00E-05

4.00E-05

5.00E-05

6.00E-05

7.00E-05

8.00E-05

9.00E-05

500 600 700 800 900 1000 1100 1200

1-C4H8

ISO-C4H8

Temperature [K] Temperature [K]

Mol

e Fr

actio

nM

ole

Frac

tion

10 atm, φ=1, τ=0.7s, 0.1% initial fuel

- - - - detailed model______ functional group



Validation of functional group approach in counter flow flame (2- methyl heptane)

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

0 2 4 6 8 10 12 14 16 18 20

MO

LA

R C

ON

CE

NT

RA

TIO

N (

%)

DISTANCE FROM FUEL PORT (mm)

CO2

CO

C8H18-2

0

200

400

600

800

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1200

1400

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1800

0 2 4 6 8 10 12 14 16 18 20

TEM

PER

ATU

RE

(K)


measuredcorrectedmodelFunctional Group Model

0

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7000

2 4 6 8 10

MO

LAR

CO

NC

ENTR

ATIO

N (P

PM)


C2H4

C2H2

CH4

0

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500

2 4 6 8 10

MO

LAR

CO

NC

ENTR

ATIO

N (P

PM)


iC4H8

1-C4H8+1,2-C3H4

The model successfully reproduces the flame temperature profile as well as the flame structure

_______ Detailed model _____ Functional group approach



Mechanisms are available on LLNL website and by email

http://www-pls.llnl.gov/?url=science_and_technology-chemistry-combustion

LLNL-PRES-427539



Collaborations

Our major current industry collaboration is via the DOE working groups on HCCI and diesel engines • All results presented at Advanced Engine Combustion Working

group meetings (Industry, National labs, U. of Wisc., U. of Mich.)• Collaboration with John Dec at Sandia on HCCI engine

experiments Second interaction is collaboration with many universities

• Dr. Curran at Nat’l Univ. of Ireland on 2-methyl heptane & other fuels

• Prof. Egolfopoulos at USC on 2-methyl heptane• Prof. Seshadri at UC San Diego on 2-methyl heptane and toluene• Prof. Oehlschaeger at RPI on large alkanes• Prof. Sung’s group, U of Conn. on gasoline surrogates• Prof. Lu, U. of Conn. & Prof. Chen, UCB on mechanism reduction

Participation in other working groups with industrial representation• Fuels for Advanced Combustion Engines (FACE) Working group

and AVFL-18 (Surrogate fuels for kinetic modeling)



Activities for Next Fiscal Year Develop detailed chemical kinetic

models for another series iso-alkanes:di-methyl alkanes

Validation of 2 and 3-methyl alkanes mechanisms with new data from shock tubes, jet-stirred reactors, and counterflow flames

Develop detailed chemical kinetic models for larger alkyl aromatics:

Develop more accurate surrogates for gasoline Further develop mechanism reduction using functional group

methodn-decyl-cyclohexane - Diesel fuels



Summary Approach to research

• Continue development of surrogate fuel mechanisms to improve engine models for HCCI and diesel engines

Technical accomplishments:• We validated our 2-methyl alkane mechanism on a wide set of

experimental data and improved the model Collaborations/Interactions

• Collaboration through AEC working group and FACE working group with industry. Many collaborators from national labs and universities

Plans for Next Fiscal Year:• Larger alkyl aromatics:

Documents

Lawrence Livermore National Laboratory · Washington, DC. This presentation does not contain any proprietary, confidential or otherwise restricted information This work performed