lawrence livermore national laboratory · washington, dc. this presentation does not contain any...
Post on 09-Jul-2020
2 Views
Preview:
TRANSCRIPT
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
Lawrence Livermore National Laboratory
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
3LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
4LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
5LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
6LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
7LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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.
8LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
9LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
10LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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)
11LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
12LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
13LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
14LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
15LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
16LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
17LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
18LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
10
12
14
16
-3 -2 -1 0 1 2 3 4
PRFs
Higher unsaturated content
Slope
Sens
itiv
ity
a)
Sensitivity vs. Slope
25 atm
19LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
20LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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:
21LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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:
2100 Species 8150 Reactions
JSR
Traditional Approach:
7900 Species 27000 ReactionsProposed Approach:
280 Species 1500 Reactions
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:
22LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
23LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
1000
1200
1400
1600
1800
0 2 4 6 8 10 12 14 16 18 20
TEM
PER
ATU
RE
(K)
DISTANCE FROM FUEL PORT (mm)
measuredcorrectedmodelFunctional Group Model
0
1000
2000
3000
4000
5000
6000
7000
2 4 6 8 10
MO
LAR
CO
NC
ENTR
ATIO
N (P
PM)
DISTANCE FROM FUEL PORT (mm)
C2H4
C2H2
CH4
0
50
100
150
200
250
300
350
400
450
500
2 4 6 8 10
MO
LAR
CO
NC
ENTR
ATIO
N (P
PM)
DISTANCE FROM FUEL PORT (mm)
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
24LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
Mechanisms are available on LLNL website and by email
http://www-pls.llnl.gov/?url=science_and_technology-chemistry-combustion
LLNL-PRES-427539
25LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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)
26LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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
27LLNL-PRES- 472814 2011 DOE Merit Review
Lawrence Livermore National Laboratory
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:
top related