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

The Effect of In-Cylinder Turbulence on Lean, Premixed, Spark-Ignited Engine Performance

[+] Author and Article Information
Baine Breaux

Hiltner Combustion Systems,
Ferndale, WA 98248
e-mail: bbb@hiltnercombustionsystems.com

Chris Hoops

Hiltner Combustion Systems,
Ferndale, WA 98248
e-mail: cmh@hiltnercombustionsystems.com

William Glewen

Hiltner Combustion Systems,
Ferndale, WA 98248
e-mail: wjg@hiltnercombustionsystems.com

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 17, 2015; final manuscript received December 15, 2015; published online March 1, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(8), 081504 (Mar 01, 2016) (11 pages) Paper No: GTP-15-1530; doi: 10.1115/1.4032418 History: Received November 17, 2015; Revised December 15, 2015

The intensity and structure of in-cylinder turbulence is known to have a significant effect on internal combustion engine performance. Changes in flow structure and turbulence intensity result in changes to the rate of heat release, cylinder wall heat rejection, and cycle-to-cycle combustion variability. This paper seeks to quantify these engine performance consequences and identify fundamental similarities across a range of high-speed, medium-bore, lean-burn, spark-ignited reciprocating engines. In-cylinder turbulence was manipulated by changing the extent of intake port-induced swirl as well as varying the level of piston-generated turbulence. The relationship between in-cylinder turbulence and engine knock is also discussed. Increasing in-cylinder turbulence generally reduces combustion duration, but test results reveal that increasing swirl beyond a critical point can cause a lengthening of burn durations and greatly reduced engine performance. This critical swirl level is related to the extent of small-scale, piston-generated turbulence present in the cylinder. Increasing in-cylinder turbulence generally leads to reduced cycle-to-cycle variability and increased detonation margin (DM). The overall change in thermal efficiency was dependent on the balance of these factors and wall heat transfer, and varied depending on the operational constraints for a given engine and application. Single cylinder engine test data, supported with three-dimensional computational fluid dynamics (CFD) results, are used to demonstrate and explain these basic combustion engine principles.

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Figures

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Fig. 2

Representative piston geometries with low (top) and high (bottom) squish velocities

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Fig. 1

Cylinder head configuration (a) and swirl coefficients as a function of valve lift (b) for high BMEP PC

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Fig. 4

Burn durations (a) and COV of IMEP and heat rejection (b) for the high BMEP PC engine as a function of PC fueling rate

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Fig. 7

Measured 10–90% burn durations (a), CFD-simulated turbulence kinetic energy (b), and measured unburned hydrocarbon emissions (c) as a function of swirl number for varying squish velocities in the high BMEP open chamber engine

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Fig. 9

COV of IMEP as a function of squish velocity (a) and swirl number (b)

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Fig. 8

Engine heat rejection as a function of squish velocity (a) and swirl number (b)

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Fig. 10

DM as a function of squish velocity (a) and swirl number (b)

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Fig. 5

0–10% burn durations as a function of squish velocity (a) and swirl number (b)

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Fig. 6

10–90% burn durations as a function of squish velocity (a) and swirl number (b)

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Fig. 12

BTE as a function of squish velocity (a) and swirl number (b). Points with uniform 50% MFB location are connected with solid lines and points with uniform DM are connected with dashed lines.

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Fig. 3

Adjustment of AFR relative to CA50 in order to maintain fixed engine-out NOx emissions (a) and selection of operating points at fixed 50% MFB location for comparison using 10–90% burn durations as an example (b)

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Fig. 13

EPT as a function of squish velocity (a) and swirl number (b) at uniform combustion phasing (solid lines) and uniform DM (dashed lines)

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Fig. 14

Minimum obtainable NOx within a specified COV of IMEP limit as a function of squish velocity (a) and swirl number (b)

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Fig. 11

COV of PCP as a function of squish velocity (a) and swirl number (b)

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