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Chemical Kinetics Studies ofAlternative Fuels
Chih-Jen (Jackie) SungDepartment of Mechanical Engineering
University of Connecticut
Prepared for2010 MACCCR and CEFRC Conferences
Princeton, NJ
September 23, 2010
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Accomplishments – Year 1
• Autoignition of n-Butanol at Low to Intermediate Temperatures and Elevated Pressures*– PC = 15 – 30 bar; TC = 675 – 925 K
• Autoignition of Methanol: Experiments and Computations– PC = 7 – 30 bar; TC = 850 – 1100 K
• Nanoparticle-Enhanced Combustion of Liquid Fuels– PC = 15 – 28 bar; TC = 772 – 825 K
• Laminar Flame Speeds of Moist Syngas Mixtures
* Bryan Weber, Kamal Kumar, Yu Zhang
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• Simulated ignition delays computed using four reaction mechanisms available in the literature are much longer than experimental ignition delays.
• Although the reaction mechanisms have not been validated in the temperature and pressure range studied here, the degree of difference is still rather surprising.
• Sensitivity analysis at low temperatures shows the impotence of hydrogen abstraction reaction from n-butanol by HO2 to formα-hydroxybutyl radical.
• Reaction path analysis on the mechanism of Black et al. (2010) reveals several pathways which may need to have their rates adjusted and at least two pathways which are missing entirely.– Propanal formation and tautomerization of but-1-en-1-ol to butanal.
Summary: n-Butanol Autoignition
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Autoignition of n-Butanol:Experiments vs. Simulations
0.01
0.1
1
10
1.15 1.2 1.25 1.3 1.35 1.4
n-Butanol/O2/N2, φ=1.0, PC=15 bar
Current DataBlack et al. (2010)Moss et al. (2008)Grana et al. (2010)Harper et al. (2010)
Igni
tion
Del
ay (s
)
1000/TC (1/K)
O2 : N2 = 1 : 3.76
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Rapid Compression Machine Operation
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Autoignition of n-Butanol:RCM Simulations
0
5
10
15
20
25
30
35
40
45
-0.02 0 0.02 0.04 0.06
n-Butanol/O2/N2, φ=1.0, PC=15 bar
Current DataBlack et al. (2010)Moss et al. (2008)Grana et al. (2010)Harper et al. (2010)
Pres
sure
(bar
)
Time (s)
TC = 758 K
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Experimental Reproducibility
• Each compressed pressure
and temperature condition
is repeated at least 6 times
to ensure reproducibility.
0
5
10
15
20
25
30
35
-0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04
n-Butanol/O2/N2, φ=1.0, PC=15 bar, TC=758 K
Pres
sure
(bar
)
Time (s)
Ignition Delay
O2 : N2 = 1 : 3.76
End of Compression
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Mixture Preparation (1)
0.01
0.1
1
101
102
103
104
250 275 300 325 350 375 400
Saturated Vapor Pressure vs. Temperature
n-butanoliso-octaneethanolmethanoln-decane
Satu
rate
d V
apor
Pre
ssur
e (T
orr)
Temperature (K)
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Mixture Preparation (2)
• Homogeneous test mixture prepared in a stirred, heated stainless steel tank of known volume– Gaseous components in the test mixture are determined
manometrically
– Liquid fuel components are added on a gravimetric basis
• Add air/fuel under ambient temperature conditions
• Preheat temperature (below the boiling points of the liquid fuel components)– Continuous magnetic stirring
– Soak time ~ 1.5 hours for complete vaporization of the liquid components
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Composition Confirmation• Liquid calibration standards and gas samples
withdrawn from the mixing tank are analyzed using GCMS
• There is no decomposition for initial mixing tank temperature of 87˚C
• iso-Octane is used as an internal standard for checking the concentration of n-butanol
• Composition checks show actual concentration is within 4% of expected concentration
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Autoignition of n-Butanol (1)
924 K906 K 898 K
879 K866 K
853 K834 K
824 K
813 K
0
5
10
15
20
25
30
35
-0.02 0 0.02 0.04 0.06 0.08 0.1
n-Butanol/O2/N2, φ=0.5, PC =15 bar
Pres
sure
(bar
)
Time (seconds)
TC
O2 : N2 = 1 : 3.76
• Increasing compressed temperature reduces ignition delay monotonically.
• No two-stage ignition and no NTC behavior found for the conditions tested.
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Autoignition of n-Butanol (2)
0.01
0.1
1 1.1 1.2 1.3 1.4 1.5
n-Butanol/O2/N2, PC = 15 bar
φ = 0.5φ = 1.0φ = 2.0
Igni
tion
Del
ay (s
)
1000/TC (1/K)
O2 : N2 = 1 : 3.76
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Autoignition of n-Butanol (3)
0.01
0.1
1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45
n-Butanol/O2/N2, PC = 15 bar
Fuel Mole % = 1.69, φ = 0.5Fuel Mole % = 6.77, φ = 2.0Fuel Mole % = 3.38, φ = 1.0
Igni
tion
Del
ay (s
)
1000/TC (1/K)
(a) O2 Mole % = 20.3
0.01
0.1
1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5
n-Butanol/O2/N2, PC = 15 bar
O2 Mole % = 40.6, φ = 0.5O2 Mole % = 10.2, φ = 2.0O2 Mole % = 20.3, φ = 1.0
Igni
tion
Del
ay (s
)
1000/TC (1/K)
(b) Fuel Mole % = 3.38
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Autoignition of n-Butanol (4)
0.01
0.1
1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5
n-Butanol/O2/N2, φ = 1.0
Igni
tion
Del
ay (s
)
1000/TC (1/K)
O2 : N2 = 1 : 3.76
PC = 15 bar
PC = 30 bar
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Autoignition of n-Butanol (5)
10-5
10-4
10-3
10-2
10-1
100
1 1.1 1.2 1.3 1.4 1.5 1.6
Correlated Ignition Delay
CorrelationExperiments
τ / (
XO
2-1.
7 Xn-
But
anol
-1.4
PC
-1.5
)
1000/TC (1/K)
τ=10A [XO2]a [Xn-Butanol]b PCn exp(Ta /TC)
A = -(8.5 ± 0.8)a = -(1.7 ± 0.2)b = -(1.4 ± 0.2)n = -(1.5 ± 0.3)Ta = 9730.3 ± 1035.5
0.0169 < Xn-Butanol < 0.06760.1015 < XO2 < 0.406
15 < PC < 30 bar675 < TC < 925 K
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Ignition Delay Comparison
10-5
0.0001
0.001
0.01
0.1
0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5
n-Butanol/O2/N2, φ = 1.0
Current Data, PC = 30 barCurrent Data, PC = 15 barHeufer et al. (2010), 10-11 barHeufer et al. (2010), 18-22 barHeufer et al. (2010), 36-42 bar
Igni
tion
Del
ay (s
)
1000/T (1/K)
O2 : N2 = 1 : 3.76
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-40 -30 -20 -10 0 10 20
NC4H9OH+HO2C4H8OH-1+H2O2
NC4H9OH+HO2C4H8OH-3+H2O2
CH3+HO2CH4+O2
H2O2(+M)2OH(+M)
HO2+OHH2O+O2
CH3+HO2CH3O+OH
CH2O+HO2HCO+H2O2
NC4H9OH+HO2C4H8OH-2+H2O2
H+O2O+OH
NC4H9OH+OHC4H8OH-3+H2O
n-Butanol/O2/N2, φ=1.0, PC =15 atm, O2 : N2 = 1 : 3.76
700 K1100 K1800 K
Percent Sensitivity
Sensitivity Analysis
• NUI mechanism is most sensitive to the reaction of n-butanol+HO2 to form α-hydroxybutyl.
• The sensitivity is significantly reduced at higher temperatures.
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Reaction Path Analysis (1)
• A Reaction Path Diagram shows the percent of
the reactant destroyed to form the product
indicated by the arrow.
• The percent destruction represents the cumulative
destruction of each reactant up to the point in time
where the mole fraction of fuel has been reduced
20% compared to the initial value.
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• n-Butanol (C4H9OH) is destroyed by H-atom abstraction producing 5 radicals.
• These radicals are not equally produced.
Reaction Path Analysis (2)
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Reaction Path Analysis (3)
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Reaction Path Analysis (4)
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Reaction Path Analysis (5)
• Several fuel decomposition pathways have been reported in the literature, but are missing from the mechanism by Black et al. (2010).
• These missing pathways, or other pathways with questionable reaction rates, may be causing the discrepancy between experimental results and simulations.
• Quantum calculations on fuel decomposition reaction rates and speciation measurements during the ignition process are needed.
800 K, 15 atm, and =1.0
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• Autoignition of Butanol Isomers
• Autoignition of other Emerging Biofuels
(e.g. iso-pentanol, 2-buten-1-ol)
• Autoignition of Gasoline/Bio-Alcohol Blends
• In situ Absorption Spectroscopy in Rapid
Compression Machine
Future Work
Chemical Kinetics Studies of�Alternative FuelsAccomplishments – Year 1Summary: n-Butanol AutoignitionAutoignition of n-Butanol:�Experiments vs. SimulationsRapid Compression Machine OperationAutoignition of n-Butanol:�RCM SimulationsExperimental ReproducibilityMixture Preparation (1)Mixture Preparation (2)Composition ConfirmationAutoignition of n-Butanol (1)Autoignition of n-Butanol (2)Autoignition of n-Butanol (3)Autoignition of n-Butanol (4)Autoignition of n-Butanol (5)Ignition Delay ComparisonSensitivity AnalysisReaction Path Analysis (1)Reaction Path Analysis (2)Reaction Path Analysis (3)Reaction Path Analysis (4)Reaction Path Analysis (5)Future Work
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