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

The Dynamics of Second Ring Flutter and Collapse in Modern Diesel Engines

[+] Author and Article Information
Chao Cheng

Energy & Automotive Research Lab,
Michigan State University,
East Lansing, MI 48824
e-mail: chengc22@msu.edu

Harold Schock

Energy & Automotive Research Lab,
Michigan State University,
East Lansing, MI 48824
e-mail: schock@egr.msu.edu

Dan Richardson

Cummins Inc,
MC 19606,
Columbus, IN 47201
e-mail: dan.e.richardson@cummins.com

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received February 27, 2015; final manuscript received March 20, 2015; published online May 12, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(11), 111504 (Nov 01, 2015) (8 pages) Paper No: GTP-15-1061; doi: 10.1115/1.4030291 History: Received February 27, 2015; Revised March 20, 2015; Online May 12, 2015

Second ring fluttering and radial ring collapse are recognized as having significant influences on engine blowby and oil consumption. As the gas flow is coupled with the piston ring motion, understanding the ring dynamics is important for understanding not only the engine blowby mechanism, but also oil consumption mechanisms and how to control them. Only second ring flutter and collapse that occurs around the top dead center (TDC) firing conditions is examined in this paper based on a modern heavy-duty diesel engine. However, the principles described are equally applicable to all engines. First, the authors describe the fundamental mechanisms of how second ring fluttering and radial ring collapse occur. This is described by examining the forces that are acting on the second ring. Then, two cases are shown. One case shows second ring flutter and the other case shows stable second ring motion. The reasons for these two different cases are explained, including the effect of static twist and the end gaps of the rings. A sensitivity study was performed to evaluate the effect of changing the top and second ring end gaps on ring lift. It was shown how the gaps could affect the second ring flutter and ring collapse. It is concluded that the second ring will be more likely to flutter or collapse if it has a negative static twist, if the second ring end gap is large, and/or if the top ring end gap is small. If the second ring does not flutter, it may still be possible to design the ring pack such that there is not any reverse blowby. However, this must be carefully studied and controlled or the second land pressures will be too high, resulting in reverse blowby and/or top ring lifting.

Copyright © 2015 by ASME
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Fig. 3

Ring collapse scenario

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Fig. 2

Second ring fluttering scenario

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Fig. 1

Ring inertial force, gas pressure force, and net force zoom-in

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Fig. 4

Inter-ring pressures and ring in-groove motion for second ring fluttering case (case 1)

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Fig. 5

Inter-ring pressures and ring in-groove motion for no second ring fluttering case (case 2)

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Fig. 6

Second land pressure for cases 1 and 2

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Fig. 7

Instantaneous gas flow across the second ring: (a) gas flow across second ring end gap and (b) gas flow across second ring sides

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Fig. 8

Simplistic illustration of ring bottom seating stability

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Fig. 14

Instantaneous gas flow through top ring end gap

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Fig. 9

Simplistic illustration of ring top seating stability

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Fig. 10

Cross-over point between in-cylinder and second land pressures

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Fig. 11

Inter-ring gas pressures and ring in-groove locations for the ring lift case

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Fig. 12

Instantaneous gas flow through second ring end gap and ring face

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Fig. 13

Inter-ring gas pressures and ring in-groove locations for cross-over case




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