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

Experimental Investigation of the Variations of Early Flame Development in a Spark-Ignition Direct-Injection Optical Engine

[+] Author and Article Information
David L. S. Hung

University of Michigan-Shanghai Jiao Tong
University Joint Institute,
National Engineering Laboratory for Automotive Electronic Control Technology,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: dhung@sjtu.edu.cn

Hao Chen

National Engineering Laboratory for
Automotive Electronic Control Technology,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: chenhow2008@sjtu.edu.cn

Min Xu

National Engineering Laboratory for
Automotive Electronic Control Technology,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: mxu@sjtu.edu.cn

Jie Yang

National Engineering Laboratory for
Automotive Electronic Control Technology,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: yangjiejt@gmail.com

Hanyang Zhuang

University of Michigan-Shanghai Jiao Tong
University Joint Institute,
Shanghai Jiao Tong University,
Shanghai 200240, China,
e-mail: zhuanghany11@sjtu.edu.cn

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 February 13, 2014; final manuscript received February 21, 2014; published online May 2, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(10), 101503 (May 02, 2014) (8 pages) Paper No: GTP-14-1086; doi: 10.1115/1.4027256 History: Received February 13, 2014; Revised February 21, 2014

Experiments under two intake air swirl levels (swirl ratios of 0.55 and 5.68) were conducted in order to investigate the early flame development of combustion in a single-cylinder spark-ignition direct-injection engine. The engine was equipped with a quartz insert in the piston, which provided an optical access to its cylinder through the piston. The crank angle resolved combustion images through the piston window and in-cylinder pressure measurements of 250 cycles were simultaneously recorded for both swirl levels at a specified engine speed and low load condition. The early development, size, and spatial characteristics extracted from the flame images were analyzed as a function of crank angle degrees after the ignition. The experimental results revealed that the early flame development was strongly influenced by the highly directed swirl motion of intake-air into the combustion cylinder. The location of the start of the flame kernel relative to the spark plug position also changed intermittently at different swirl levels. While the structure of the early flame was found to be similar for both swirl levels, the starting location of the flame showed a vast difference in how the flame progressed. In general, the flame kernel was formed two crank-angle degrees after spark timing for the high swirl level, which was four crank-angle degrees earlier than that of the low swirl case. For the low swirl flow, the early combustion showed more cycle-to-cycle variation in terms of both the flame size and centroid location. It was quantitatively shown that increasing the swirl ratio from 0.55 to 5.68 could reduce the cycle-to-cycle variation of the early flame structure, resulting in about three to four crank-angle degrees advance of the peak pressure location and a 1% improvement for the coefficient of variation (COV) of the indicated mean effective pressure (IMEP).

Copyright © 2014 by ASME
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References

Figures

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Fig. 1

Optical engine with a metal liner, pent-roof window, and upper piston with a quartz insert

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Fig. 2

Bottom view of the cylinder head; the dashed line shows the field of view (with a diameter of 26 mm)

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Fig. 3

Experimental setup of the imaging diagnostics

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Fig. 4

Processing method for extracting the boundary centroid and locations of flame images

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Fig. 5

Average in-cylinder pressure curves for the low and high swirl levels

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Fig. 6

Peak pressure of 250 consecutive combustion cycles

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Fig. 7

IMEP of 250 consecutive combustion cycles

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Fig. 8

Four representative combustion cycles of early flame development recorded from the low swirl level

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Fig. 9

Four representative combustion cycles of early flame development recorded from the high swirl level

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Fig. 10

Starting time variation of flame kernel formation (top), and CA05 location variation (bottom) over 250 combustion cycles

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Fig. 11

Cycle-to-cycle variation of centroid locations under low swirl conditions, corresponding to flame areas of 1 mm2, 3 mm2, 5 mm2, and 7 mm2, respectively

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Fig. 12

Cycle-to-cycle variation of centroid locations under high swirl conditions, corresponding to flame areas of 1 mm2, 3 mm2, 5 mm2, and 7 mm2, respectively

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Fig. 13

Distribution of the number of flame cycles reaching 1 mm2 under two swirl levels

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Fig. 14

Distribution of the number of flame cycles reaching 3 mm2 under two swirl levels

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Fig. 15

Distribution of the number of flame cycles reaching 5 mm2 under two swirl levels

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Fig. 16

Distribution of the number of flame cycles reaching 7 mm2 under two swirl levels

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Fig. 17

The correlation between the early flame (1 mm2) and peak pressure locations

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