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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Ignition and Oxidation of 50/50 Butane Isomer Blends

[+] Author and Article Information
Nicole Donato, Christopher Aul, Eric Petersen

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843

Christopher Zinner

Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, FL 32816

Henry Curran

School of Chemistry, National University of Ireland Galway, Galway, Ireland

Gilles Bourque

 Rolls-Royce Canada, Montreal, Canada H8T 1A2

http://c3.nuigalway.ie/butane.html

J. Eng. Gas Turbines Power 132(5), 051502 (Mar 04, 2010) (9 pages) doi:10.1115/1.3204654 History: Received March 26, 2009; Revised April 07, 2009; Published March 04, 2010; Online March 04, 2010

One of the alkanes found within gaseous fuel blends of interest to gas turbine applications is butane. There are two structural isomers of butane, normal butane and isobutane, and the combustion characteristics of either isomer are not well known. Of particular interest to this work are mixtures of n-butane and isobutane. A shock-tube experiment was performed to produce important ignition-delay-time data for these binary butane isomer mixtures, which are not currently well studied, with emphasis on 50-50 blends of the two isomers. These data represent the most extensive shock-tube results to date for mixtures of n-butane and isobutane. Ignition within the shock tube was determined from the sharp pressure rise measured at the end wall, which is characteristic of such exothermic reactions. Both experimental and kinetics modeling results are presented for a wide range of stoichiometries (ϕ=0.32.0), temperatures (1056–1598 K), and pressures (1–21 atm). The results of this work serve as a validation for the current chemical kinetics model. Correlations in the form of Arrhenius-type expressions are presented, which agree well with both the experimental results and the kinetics modeling. The results of an ignition-delay-time sensitivity analysis are provided, and key reactions are identified. The data from this study are compared with the modeling results of 100% normal butane and 100% isobutane. The 50/50 mixture of n-butane and isobutane was shown to be more readily ignitable than 100% isobutane but reacts slower than 100% n-butane only for the richer mixtures. There was little difference in ignition time between the lean mixtures.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

n-butane and isobutane chemical structures. Normal butane carbon atoms are arranged in one row, while isobutane has a carbon atom in the middle (4).

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Figure 8

Ignition-delay-time data compared with model results for mixture 4: 50% n-C4H10 and 50% iso-C4H10 at ϕ=2.0

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Figure 9

Ignition delay times obtained from the mechanism are plotted against inverse temperature at 8 atm for a wide range of stoichiometry. Fuel lean conditions show similar ignition times for n-C4H10 and iso-C4H10; however, under stoichiometric and fuel rich conditions, n-C4H10 and iso-C4H10 have significantly different ignition times. (a) ϕ=0.3, (b) ϕ=0.5, (c) ϕ=1.0, and (d) ϕ=2.0.

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Figure 10

High-temperature correlation from Eq. 2. Experimental data, correlation results, and mechanism predictions plotted against inverse temperature show good agreement for high temperatures (τ in μs; [fuel] and [air] in mol/cm3).

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Figure 11

Low-temperature correlation of Eq. 3. A shallower slope is seen for the lower temperature experimental data, correlation, and mechanism predictions when plotted against inverse temperature (τ in μs; [fuel] and [air] in mol/cm3).

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Figure 12

Sensitivity analysis results from OH∗ show the most important reactions as a function of time during ignition. Sensitivity results for low pressure (1.8 atm) and low temperature (1050 K).

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Figure 13

Sensitivity analysis results from OH∗ show the most important reactions as a function of time during ignition. Results shown for high pressure (18.6 atm) and low temperature (1050 K).

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Figure 14

Sensitivity analysis results from OH∗ show the most important reactions as a function of time during ignition. Sensitivity results show that the key reactions for fuel rich conditions are different from those reactions for fuel lean conditions at low pressure (1 atm) and low temperature (1050 K).

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Figure 15

Sensitivity analysis results from OH∗ show the most important reactions as a function of time during ignition. Sensitivity analysis results show that the important reactions for fuel rich conditions are different from those reactions for fuel lean conditions at high pressure (18 atm) and high temperature (1400 K).

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Figure 2

Validation of model for 100% n-butane in air (ϕ=1) over a wide range of conditions. Points are experimental results; lines are model simulations. Data are from Ref. 29.

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Figure 3

Schematic of shock-tube facility presented in Aul (31)

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Figure 4

Typical end wall pressure and emission traces used to determine ignition delay time. No early reaction leading to accelerated main ignition is seen in either the pressure or OH∗ traces. (a) Long test time example: T=1105 K and τign=1959 μs. (b) Typical test time example: T=1179 K and τign=600 μs.

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Figure 5

Ignition-delay-time data compared with model results for mixture 1: 50% n-C4H10 and 50% iso-C4H10 at ϕ=0.3

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Figure 6

Ignition-delay-time data compared with model results for mixture 2: 50% n-C4H10 and 50% iso-C4H10 at ϕ=0.5

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Figure 7

Ignition-delay-time data compared with model results for mixture 3: 50% n-C4H10 and 50% iso-C4H10 at ϕ=1.0

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