lawrence livermore national laboratory
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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 15, 2012
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-543385
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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:• FY11: 500K• FY12: 640K
Timeline
Budget
Barriers/Targets
• Project Lead: LLNL – W. J. Pitz (PI), C. K. Westbrook, M. Mehl, S. 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
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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
FY12 Objectives:• Develop detailed chemical kinetic models for larger alkyl aromatics• Develop a reduced surrogate mechanism for diesel to be used for
multidimensional CFD simulations • Develop more accurate surrogate kinetics models for gasoline • Develop a functional group method to represent cycloalkanes in diesel
fuel• Validate and improve 2- and 3-methyl alkanes mechanisms with new
data from shock tubes, jet-stirred reactors, counterflow flames, and premixed flames
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Chemical kinetic milestones January, 2012
Develop more accurate surrogate kinetics models for gasoline • June, 2012
Develop a functional group method to represent cycloalkanes in diesel fuel• June, 2012
Develop detailed chemical kinetic models for larger alkyl aromatics• September, 2012
Develop a reduced surrogate mechanism for diesel to be used for multidimensional CFD simulations
• September, 2012Validate and improve 2- and 3-methyl alkanes mechanisms with new data from shock tubes, jet-stirred reactors, counterflow flames, and premixed flames
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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
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Technical Accomplishment Summary
Development of chemical kinetic model for larger aromatics
Determined effect of branching for alkanes on ignition under engine conditions
Validated approach and mechanism for gasoline surrogate fuels
RCM
Shock tube
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
0.7 1.2
Igni
tion
Del
ay T
ime
(s)
1000/T (1/K)
Octane isomersphi=1, 20 atm, in air
2mhp
nc8
3mhp
0.1
1
10
100
0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6
Current WorkRCM SimulationGauthier et al. (2004)Constant Volume Simulation
Tota
l Ign
ition
Del
ay (m
s)
1000/TC (K-1)
(b) φ=1.0, PC=40 bar
Developing reduced chemical kinetic model for diesel for engine combustion network (ECN)
0
200
400
600
800
1000
1200
550 600 650 700 750 800 850
Temperature [K]
CO
[ppm
]
Flow Reactor Data8 bar
Ф = 0.23(23% m-xylene /
77% n-dodecane)
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Fuel Surrogate Palette for Diesel
n-alkanebranched alkanecycloalkanesaromaticsothers
butylcyclohexanedecalin
hepta-methyl-nonane
n-decyl-benzenealpha-methyl-naphthalene
n-dodecanen-tridecanen-tetradecanen-pentadecanen-hexadecane
tetralin
Need representative component models to fill outthe diesel fuel surrogate palette:
trimethyl-
2,9-dimethyldecane
2-methylpentadecane
3-methyldodecane
Lightly methylated iso-alkanes
Large aromatics
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Jet Stirred Reactors
• Idealized chemical reactors with/without simplified transport phenomenon
Non Premixed Flames
Premixed Laminar Flames
Engine Combustion
Combustion Parameters
Temperature
Pressure
Mixture fraction (air-fuel ratio)
Mixing of fuel and air
Need to validate the fuel component and surrogate models
Shock tube
Electric ResistanceHeater
Evaporator
Fuel Inlet
Slide Table
Oxidizer Injector
Optical Access Ports
Sample ProbeWall Heaters
High pressure flow reactors
Rapid Compression Machine
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Modeling of 3-methylheptane Ignition
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
0.7 0.9 1.1 1.3 1.5
Igni
tion
Del
ay T
ime
(s)
1000/T (1/K)
3-methylheptane 20 atm, in air
3mhp phi=0.5 3mhp 3mhp phi=1.0 3mhp 3mhp phi=2 3mhp
Model is generally within a factor of 1.5-2 of the experimental data.
Model slightly faster than shock tube data in the NTC region
3-methylheptane
!=0.5 !=1
!=2
Shock tube
W. Wang, Li, Oehlschlaeger, Healy, Curran, Sarathy, Mehl, Pitz, Westbrook, Proc. Combust. Inst. (2012).
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Modeling the effect of branching on ignition
-19.0
21.7
36.8
RON
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
0.7 0.9 1.1 1.3 1.5
Igni
tion
Del
ay T
ime
(s)
1000/T (1/K)
Octane isomersphi=1, 20 atm, in air
2mhp
nc8
3mhp
iso-octane
100
iso-octane
3-methylheptane
n-octane
2-methylheptane
Shock tube
W. Wang, Li, Oehlschlaeger, Healy, Curran, Sarathy, Mehl, Pitz, Westbrook, Proc. Combust. Inst. (2012).
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Jet Stirred Reactor (JSR) 3-methylheptane CNRS Orleans, France
•! The zero dimensional perfectly system is ideal for modeling.
•! The products species profiles are dependent on chemical kinetics due to the perfectly mixed homogeneous environment.
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0.0E+00
2.0E-04
4.0E-04
6.0E-04
8.0E-04
1.0E-03
1.2E-03
1.4E-03
500 600 700 800 900 1000 1100 1200
Mol
e Fr
actio
n
Temperature (K)
JSR 3-Methylheptane Results
Good prediction of low T and high T reactivity
Fuel
C2H4
H2
! = 1 10 atm
Dagaut et al. CNRS (2010)
Experiments performed at CNRS, Orleans (F. Karzenty, C. Togbe G. Dayma, P. Dagaut)
Lines: LLNL model
Curves: CNRS experiments
" = 0.7 sec
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Model simulations and experiments show decrease in laminar flame speeds with branching for octane isomers
#!Important to properly predict flame speeds for gas turbine applications
#!Location of single methyl branch has minimal effect on flame speed
!"#
$%#
$"#
&%#
&"#
'%#
'"#
"%#
""#
%()# %(*# !(%# !($# !('# !()#
!"#$%"&'()"#*'+,**-.'+/0
'12#345'
67/$8")*%2*'9":0'
+,-.#&"&#/.#!+01#2342-,12506#76819:;6<.#1:=2;#7;,526<#
5>:?0+52###$>120@8;@240+52###&>120@8;@240+52###$.">=,120@8;@23+52###
n-octane
Experiments: symbols
Model: lines
2,5-dimethylhexane Experiments performed at USC, Los Angeles
3-methylheptane
2-methylheptane
Lam
inar
flam
e sp
eed
[cm
/s]
Equivalence ratio
(LLNL)
(USC) Ji, Sarathy, Veloo, Westbrook and Egolfopoulos, Combust. Flame (2012)
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Developed new procedure to formulate gasoline surrogates
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
Dela
y Tim
es [s
]25 atm
1000K/T
T=825 K
Experimental data: Personal communication and N. Morgan et al. Comb. & Flame
slope
40 different gasoline surrogates were simulated
Slope in NTC region correlates to octane sensitivity = RON - MON
Ignition delay at 825K correlates to octane number
FY2011
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A correlation between the octane rating and the autoignition propensity of gasoline surrogate fuels has been identified
y = -0.60x2 + 2.64x + 8.86R² = 0.79
-2
0
2
4
6
8
10
12
14
16
-3 -2 -1 0 1 2 3 4
PRFs
Higher unsaturated content
Slope
Sens
itivi
ty
a) 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)] O
I
b)
Sensitivity vs. Slope Octane Index vs. Ignition Delay time @ 825K
Starting from the analysis of 40 different fuel mixtures a general approach to the formulation of the gasoline surrogate has been developed on the basis of the key features of the ignition delay curves
25 atm
FY2011
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Surrogate (%Vol)
RD387 Gasoline (%Vol)
i-Alkanes 57n- Alkanes 16Aromatics 23 23
Olefins 4.0 4.2
73
Matched gasoline properties with a surrogateAlkanes
Aromatics
Olefins
FY2011
A/F Ratio 14.6 14.8H/C 1.93 1.95
Octane index 87 87Sensitivity 8.0 7.6
Composition:
Other properties:
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Simulations of real gasoline (RD387) experiments using LLNL surrogate model
0.01
0.1
1
10
100
0.6 0.8 1 1.2 1.4 1.6
Current WorkGauthier et al. (2004)RCM SimulationConstant Volume Simulation
Tota
l Ign
ition
Del
ay (m
s)
1000/TC (K-1)
(a) φ=1.0, PC=20 bar
0.1
1
10
100
0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6
Current WorkRCM SimulationGauthier et al. (2004)Constant Volume Simulation
Tota
l Ign
ition
Del
ay (m
s)
1000/TC (K-1)
(b) φ=1.0, PC=40 bar
RCM experiments: G. Kukkadapu, K. Kumar, C.-J. Sung, Univ. of ConnecticutShock tube experiments: Gauthier, Davidson and Hanson, 2004
RCM
Shock tube
RCM
RCM model
Constant volume model
Curves: LLNL modelSymbols:○ Univ. Conn. experiments□ Stanford experiments
Curves: LLNL modelSymbols:○ Univ. Conn. experiments□ Stanford experiments
RCM
Shock tube RCM model
Constant volume model
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Purely experimental comparisons of LLNL and Stanford surrogate formulation with real gasoline: LLNL formulation matches well real gasoline
0
5
10
15
20
25
30
35
40
-20 -15 -10 -5 0 5 10
(a) φ=1, PC=20 bar, TC=758 K
Pres
sure
(bar
)
Time (ms)
LLNL
Gasoline
Stanford A
0
10
20
30
40
50
60
70
80
-20 -15 -10 -5 0 5 10 15
(c) φ=1, PC=40 bar, TC=688 K
Pres
sure
(bar
)Time (ms)
Stanford A
Gasoline
LLNL
RCM experiments:
G. Kukkadapu, K. Kumar, C.-J. Sung, Univ. of Conn.
(RD387)
(RD387)
RCM
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Surrogate for larger alkyl aromatics: n-heptane + n-propylbenzene
6 7 8 9 10 11 12 13 14 15 160.01
0.1
1
10
100
1 atm 10 atm 30 atm
Igni
tion
dela
y tim
e / m
s
10,000 K / T
Curves: NUIG-LLNL model
Experiments: NUIG
1 atm
10 atm
30 atmshock tube
Rapid compression machine
with heat loss model
Experimental RCM data: Darcy and Curran, NUIG, 2011
Shock tube
10 atm
ɸ= 0.98
43% n-heptane /57% n-propylbenzene in air
Shock tube study: Darcy, Mehl, Simmie, Wurmel, Metcalfe, Pitz and Curran, Proc. Combust. Inst. (2012)
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Larger aromatics: Shock tube ignition of n-butyl benzene at high pressure
n-butylbenzene
Experiments: Tobin,Yasunaga and Curran, NUIG, Ireland (Combust. Flame 2011)
1E-05
0.0001
0.001
0.01
0.6 0.7 0.8 0.9 1.0 1.1
Igni
tion
dela
y tim
e [m
s]
1000 K / T
1 atm10 atm
30 atm
φ=0.5
Curves: NUIG-LLNL model
Symbols: NUIG experiments
Shock tube
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Developing reduced model for diesel surrogate for Engine Combustion Network (ECN) (23% m-xylene / 77% n-dodecane)
(by liquid volume)
CO formation is a good index of the reactivity of the mixtureGood predictions on the peak value, but shifted by 40K Reasonable agreement on the flame speed measurements
Flow reactor data: Natelson, Kurman, Johnson, Cernansky, and Miller, Combust. Sci. Tech. (2011)Flame data: Ji, Moheet, Wang, Colket, Wang, Egolfopoulos, Combustion Meeting, 2011
0
200
400
600
800
1000
1200
550 600 650 700 750 800 850
Temperature [K]
CO
[ppm
]
Flow Reactor Data8 bar
Ф = 0.23
LLNL detailed model results:
010203040506070
0.6 0.8 1.0 1.2 1.4 1.6
Flam
e sp
eed
[cm
/s]
φ
1 atmTunburned = 403K
Flame speed comparisons
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Mechanisms are available on LLNL website and by email
LLNL-PRES-427539
http://www-pls.llnl.gov/?url=science_and_technology-chemistry-combustion
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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 with
gasoline • Collaboration with Sibendu Som at Argonne on diesel reacting sprays
Second interaction is collaboration with many universities• Prof. Sung’s group, U of Conn. on gasoline surrogates• 2-methyl, 3-methyl and dimethyl alkanes:
− Prof. Oehlschlaeger at RPI, shock tube ignition at engine pressures − Prof. Egolfopoulos at USC flame speed, ignition and extinction− Prof. Seshadri at UC San Diego: flame ignition and extinction− Dr. Dagaut, CNRS, Orleans, France
• Dr. Curran at Nat’l Univ. of Ireland on 2-methyl, 3-methyl heptane, n-propyl benzene and n-butyl benzene in RCM and shock tube
• Prof. Lu, U. of Conn. 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)
• Engine combustion network (ECN)
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Activities for Next Fiscal Year
Develop detailed chemical kinetic models for: • larger alkyl aromatics
• larger n-alkanes (above C16)(important to get end of distillation curve)
(both coordinated with CRC AVFL-18, “Surrogate fuels for kinetic modeling”)
Modeling of engine combustion with reduced models for diesel surrogate fuels for the Engine Combustion Network
Gasoline surrogate work with Prof. Sung (UConn) for RCM ignition and Egolfopoulos (USC) for flame speeds• Look at the effect of EGR
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Summary Approach to research
• Continue development of surrogate fuel mechanisms to improve engine models for HCCI and diesel engines
Technical accomplishments:• We validated our 3-methyl, 2-5-dimethyl alkane, and alkylated
aromatics mechanisms by comparison to experimental data at engine-like pressures and temperatures
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:• Reduced models for engine combustion network (ECN)• Validate gasoline surrogate mechanism with experiments
including EGR