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

Validation of a Newly Developed n-Heptane Reduced Chemistry and Its Application to Simulations of Ignition Quality Tester, Diesel, and HCCI Combustion

[+] Author and Article Information
Hsin-Luen Tsai

Department of Electronic Engineering,
Advanced Engine Research Center,
Kao Yuan University,
Kaohsiung, Taiwan
e-mail: hsinluen@gmail.com

J.-Y. Chen

Department of Mechanical Engineering,
University of California at Berkeley,
Berkeley, CA 94720
e-mail: jychen@me.berkeley.edu

Gregory T. Chin

Department of Mechanical Engineering,
University of California at Berkeley,
Berkeley, CA 94720
e-mail: gchin@berkeley.edu

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received October 16, 2013; final manuscript received June 18, 2014; published online July 15, 2014. Assoc. Editor: Stani Bohac.

J. Eng. Gas Turbines Power 136(12), 121505 (Jul 15, 2014) (9 pages) Paper No: GTP-13-1377; doi: 10.1115/1.4027891 History: Received October 16, 2013; Revised June 18, 2014

A skeletal mechanism (144 species) and a corresponding reduced mechanism (62 species) were developed on the basis of the most recent detailed n-heptane mechanism by Lawrence Livermore National Laboratories (LLNL, version 3.1, 2012) (Mehl et al., 2011, “Kinetic Modeling of Gasoline Surrogate Components and Mixtures Under Engine Conditions,” Proc. Combust. Inst., 33, pp. 193–200), in order to assess the mechanism's performance under various practical combustion conditions. These simplified mechanisms were constructed and validated under shock tube conditions. Three-dimensional computational fluid dynamics (3D CFD) simulations with both simplified mechanisms were conducted for the following modeling applications: ignition quality tester (IQT), diesel engine, and homogeneous charge compression ignition (HCCI) engine. In comparison with experimental data, the simulation results were found satisfactory under the diesel condition but inaccurate for both the IQT and HCCI conditions. For HCCI, the intake temperature used in the simulation had to be increased 30 K in order to be consistent with the engine data provided by Guo et al. (2010, “An Experimental and Modeling Study of HCCI Combustion Using n-Heptane,” ASME J. Eng. Gas Turbines Power, 132(2), 022801). Exploration of possible causes is conducted leading to the conclusion that refinement in the mechanism is needed for accurate prediction of combustion under IQT and HCCI conditions.

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Fig. 1

Comparison of predicted ignition delays against experimental data [14] (symbols) for equivalence ratio φ = 1 at 3.2 bar, 13.5 bar, and 40 bar. Solid lines: detailed LLNL n-heptane mechanism [4]; dashed lines: 144-species skeletal mechanism; short-dashed lines: 62-species reduced chemistry.

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Fig. 2

Block structure of the ∼60,000 cell IQT grid

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Fig. 3

Comparison of computed pressure traces during IQT auto-ignition. Solid line: 144-species skeletal mechanism; dashed line: 62-species reduced mechanism.

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Fig. 4

Contour plot of computed IQT temperature at ∼2 ms

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Fig. 5

Computed temperature of all IQT cells versus equivalence ratio

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Fig. 6

Comparison of shock tube data [14] at 13 bar for rich mixtures at equivalence ratio φ = 2. Solid lines: detailed mechanism; dashed lines: skeletal mechanism; dotted lines: reduced chemistry.

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Fig. 7

Block structure of the diesel engine grid at −20 CAD ATDC

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Fig. 8

The pressure trace under different EGRs: case 1 (0% EGR, top-left), case 2 (10% EGR, top-right), case 3 (17.5% EGR, bottom-left), and case 4 (25.9% EGR, bottom-right)

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Fig. 9

The effect of injection timing on high EGR: case 5 (SOI −3.4 deg ATDC, 25.77% EGR, top-left), case 6 (SOI −7.0 deg ATDC, 25.00% EGR, top-right), case 7 (SOI −11.1 deg ATDC, 26.90% EGR, bottom-left), and case 8 (SOI −20.0 deg ATDC, 25.54% EGR, bottom-right)

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Fig. 10

The effects of engine load and speed on engine performance: case 9 (SOI −0.8 deg ATDC, 0.70% EGR at 1250 rpm, φ = 0.35, left) and case 10 (SOI 0.5 deg ATDC, 11.68% EGR at 1750 rpm, φ = 0.79, right)

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Fig. 11

CFR engine grid for Converge [16]

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Fig. 12

Comparison of the effective intake mixture temperature obtained from the Sjöberg and Dec [35] correlation (symbols) and the Converge [16] simulation results (line)

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Fig. 13

Comparison of in-cylinder pressure obtained from experimental results [34] and from Converge [16]. Solid line: skeletal mechanism (skel144) with spray; dashed-dotted line: skeletal mechanism (skel144) without spray; short-dashed line: reduced mechanism (red62) with spray; long-dashed line: reduced mechanism (red62) with spray and 25% speed-up. All simulations are run with intake temperature at 350 K except for the accelerated reduced chemistry (red62 + 25%) which is run at 320 K.

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Fig. 14

Comparison of ignition delays for equivalence ratio φ = 0.5 at 13.5 bar. Symbols: shock tube data; solid line: detailed mechanism; dashed line: skeletal mechanism; short-dashed line: reduced mechanism; dashed-dotted line: reduced mechanism with 25% faster rates.

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Fig. 15

Comparison of ignition delays for equivalence ratio φ = 0.3 at various pressures. Solid lines: detailed mechanism; dashed line: skeletal mechanism; short-dashed line: reduced mechanism.




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