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

Experimental and Computational Study of n-Heptane Autoignition in a Direct-Injection Constant-Volume Combustion Chamber

[+] Author and Article Information
James C. Allen

The University of Alabama,
Department of Mechanical Engineering,
P.O. Box 870276,
Tuscaloosa, AL 35487
e-mail: jallen2@crimson.ua.edu

William J. Pitz

Lawrence Livermore National Laboratory,
Chemical Sciences Division,
Physical and Life Sciences Directorate,
P.O. Box 808,
Livermore, CA 94551
e-mail: pitz1@llnl.gov

Brian T. Fisher

The University of Alabama,
Department of Mechanical Engineering,
P.O. Box 870276,
Tuscaloosa, AL 35487
e-mail: bfisher@eng.ua.edu

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received March 6, 2014; final manuscript received March 7, 2014; published online April 18, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(9), 091510 (Apr 18, 2014) (8 pages) Paper No: GTP-14-1143; doi: 10.1115/1.4027194 History: Received March 06, 2014; Revised March 07, 2014

The purpose of this study was to characterize experimental n-heptane combustion behavior in a direct-injection constant-volume combustion chamber (DI-CVCC), using chamber pressure to infer ignition delay and heat-release rate. Measurements generally displayed expected trends and indicated entirely premixed combustion with no mixing-controlled phase. A significant finding was the observation of negative temperature coefficient (NTC) behavior. Comparing results with CHEMKIN-PRO simulations, it was found that a homogeneous combustion model was reasonably accurate for ignition delays longer than 5 ms. The combination of NTC behavior and homogeneous fuel-air mixtures suggests that this DI-CVCC can be useful for validation of chemical-kinetic mechanisms.

Copyright © 2014 by ASME
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Fig. 1

Schematic of CID system and important subsystems

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Fig. 2

Typical filtered pressure trace (Case 1—BASE)

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Fig. 3

Experimental pressure traces, averaged for all relevant injections, for: (a) Cases 1, 2, and 3, with varying pressure (shaded areas indicate full range of acquired data); (b) Cases 1, 4, and 5, with varying temperature; (c) Cases 1, 6, and 7, with varying injection duration; and (d) Cases 1, 8, and 9, with multiple varying parameters but constant global equivalence ratio

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Fig. 4

Ignition delay versus temperature (shown as 1000/T) for both experiments and model computations. In the top plot, temperatures for experimental data points were those measured in the chamber wall. In the bottom plot, experimental temperatures were lowered by 60 °C (see text). Experimental conditions were: Pchamber = 5 bar, DOI = 1000 μs. Simulation parameters were: P0 = 5 bar, Φ = 0.65 (based on shifted experimental temperatures).

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Fig. 5

Experimental and simulated pressure data for Case 1 (BASE). Simulation parameters were: P0 = 9.8 bar; T0 = 524 °C; Φ = 0.83.

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Fig. 6

Apparent heat release rate (Case 1—BASE), normalized to unity

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Fig. 7

Φmodel/Φglobal ratio versus ignition delay, where Φmodel has been adjusted to obtain a match in experimental and computational ignition delay




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