chemical kinetics studies of alternative fuels€¦ · september 23, 2010. accomplishments – year...

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

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

• 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

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

Rapid Compression Machine Operation

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

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

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)

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

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

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.


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


0.01

0.1

1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45


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


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


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


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

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

-40 -30 -20 -10 0 10 20

NC4H9OH+HO2C4H8OH-1+H2O2


CH3+HO2CH4+O2

H2O2(+M)2OH(+M)

HO2+OHH2O+O2

CH3+HO2CH3O+OH

CH2O+HO2HCO+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.

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.

• n-Butanol (C4H9OH) is destroyed by H-atom abstraction producing 5 radicals.

• These radicals are not equally produced.



• 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

• 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

chemical kinetics studies of alternative fuels€¦ · september 23, 2010. accomplishments – year...

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