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Research Papers: Internal Combustion Engines

Numerical and Experimental Characterization of a Natural Gas Engine With Partially Stratified Charge Spark Ignition

[+] Author and Article Information
E. C. Chan1

Clean Energy Research Centre, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada

M. H. Davy

Clean Energy Research Centre, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada

G. de Simone

Dipartimento di Ingegneria Meccanica, Università di Roma “Tor Vergata”, Rome, 00133, Italy

V. Mulone1

Dipartimento di Ingegneria Meccanica, Università di Roma “Tor Vergata”, Rome, 00133, Italy

1

Corresponding author.

J. Eng. Gas Turbines Power 133(2), 022801 (Oct 25, 2010) (8 pages) doi:10.1115/1.4000855 History: Received May 07, 2009; Revised November 03, 2009; Published October 25, 2010; Online October 25, 2010

This paper outlines the development of a comprehensive numerical framework for the partially stratified charge (PSC) lean-burn natural gas engine. A 3D model of the engine was implemented to represent fluid motion and combustion. The spark ignition model was based on the works of Herweg and Maly (1992, “A Fundamental Model for Flame Kernel Formation in SI Engines,” SAE Technical Publication, Paper No. 922243) and Tan and Reitz (2006, “An Ignition and Combustion Model Based on the Level-Set Method for Spark Ignition Engine Multidimensional Modeling,” Combust. Flame, 145, pp. 1–15). The EDC model (Ertesvåg and Magnussen, 2000, “The Eddy Dissipation Turbulence Energy Cascade Model,” Combust. Sci. Technol., 159, pp. 213–235) with a two-step mechanism was used to model natural gas turbulent combustion process. An open geometry simulation strategy was adopted to account for intake-exhaust gas and valve movements. Each simulation was executed for multiple cycles to produce a representative residual gas fraction. The numerical results were compared with the experimental data obtained on the Ricardo Hydra single cylinder research engine for both homogeneous and PSC cases and they were found to be in excellent agreement in pressure trace and heat release rate. The detailed investigation of the numerical data showed the development of an ignitable mixture under PSC cases, allowing stable kernel growth well beyond the lean misfire limit of the bulk mixture. Furthermore, limits on successful ignition can be identified using the ignition model, which exhibited self-similar behavior in terms of flame speed and turbulent fluctuation. It can also be shown that, at ultralean air-fuel ratios, the PSC plume helps replicate the ignition conditions that can be found under stoichiometric operation.

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Figures

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Figure 1

(a) A PSC spark-plug injector and (b) implementation of the PSC spark ignition system on the Ricardo Hydra SCRE

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Figure 2

(a) Ignition delay as function of turbulent fluctuation at different air-fuel ratios and (b) ignition maturity in relation to normalized time and the turbulent ignition parameter U′

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Figure 3

Comparison between experimental (24) and numerical kernel growth data from the present study

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Figure 4

Combustor geometry of Bentebbiche (39)

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Figure 5

Qualitative comparison of reaction rate between the numerical experimental results from the present study and Bentebbiche (39) at ϕ=0.9 and ϕ=0.75

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Figure 6

Computational grid for the Ricardo Hydra PSC simulation at TDC

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Figure 7

Mesh details in the vicinity of the PSC spark-plug

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Figure 8

Pressure trace and heat release rate of homogeneous and PSC combustion cases for the Ricardo Hydra SCRE. All cases are performed at 2000 RPM and WOT with 100 consecutive samples (key: —— numerical result; — — experimental mean value; - - - 2 SD from experimental mean; ⋅ ⋅ ⋅ experimental peak pressure scatter)

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Figure 9

Distribution of λ and stream function for the case of PSC at λ=1.68 in the vicinity of the spark-plug injector at the end of injection process

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Figure 10

Temperature distribution for all operating cases during the combustion process

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Figure 11

Post-combustion (+20 deg TDC) CH4 mass fraction distribution of the PSC injection near the spark-plug for λ=1.53 and λ=1.68

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