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Research Papers: Internal Combustion Engines

On the Reduction of Combustion Noise by a Close-Coupled Pilot Injection in a Small-Bore Direct-Injection Diesel Engine

[+] Author and Article Information
Stephen Busch

Sandia National Laboratories,
Livermore, CA 94551
e-mail: sbusch@sandia.gov

Kan Zha

Sandia National Laboratories,
Livermore, CA 94551
e-mail: kzha@sandia.gov

Alok Warey

General Motors,
Warren, MI 48093
e-mail: alok.warey@gm.com

Francesco Pesce

General Motors,
Torino 10129, Italy
e-mail: francesco_concetto.pesce@gm.com

Richard Peterson

General Motors,
Warren, MI 48093
e-mail: richard.peterson@gm.com

Contributed by the IC Engine Division of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received January 27, 2016; final manuscript received February 3, 2016; published online April 12, 2016. Editor: David Wisler.The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Eng. Gas Turbines Power 138(10), 102804 (Apr 12, 2016) (13 pages) Paper No: GTP-16-1041; doi: 10.1115/1.4032864 History: Received January 27, 2016; Revised February 03, 2016

For a pilot–main injection strategy in a single-cylinder light-duty diesel engine, the dwell between the pilot- and main-injection events can significantly impact combustion noise. As the solenoid energizing dwell decreases below 200 μs, combustion noise decreases by approximately 3 dB and then increases again at shorter dwells. A zero-dimensional thermodynamic model has been developed to capture the combustion noise reduction mechanism; heat release (HR) profiles are the primary simulation input and approximating them as top-hat shapes preserves the noise reduction effect. A decomposition of the terms of the underlying thermodynamic equation reveals that the direct influence of HR on the temporal variation of cylinder pressure is primarily responsible for the trend in combustion noise. Fourier analyses reveal the mechanism responsible for the reduction in combustion noise as a destructive interference in the frequency range between approximately 1 kHz and 3 kHz. This interference is dependent on the timing of increases in cylinder pressure during pilot HR relative to those during main HR. The mechanism by which combustion noise is attenuated is fundamentally different from the traditional noise reduction that occurs with the use of long-dwell pilot injections, for which noise is reduced primarily by shortening the ignition delay of the main injection. Band-pass filtering of measured cylinder pressure traces provides evidence of this noise reduction mechanism in the real engine. When this close-coupled pilot noise reduction mechanism is active, metrics derived from cylinder pressure such as the location of 50% HR, peak HR rates, and peak rates of pressure rise cannot be used reliably to predict trends in combustion noise. The quantity and peak value of the pilot HR affect the combustion noise reduction mechanism, and maximum noise reduction is achieved when the height and steepness of the pilot HR profile are similar to the initial rise of the main HR event. A variation of the initial rise rate of the main HR event reveals trends in combustion noise that are the opposite of what would happen in the absence of a close-coupled pilot. The noise reduction mechanism shown in this work may be a powerful tool to improve the tradeoffs among fuel efficiency, pollutant emissions, and combustion noise.

Copyright © 2016 by ASME
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References

Figures

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Fig. 1

Experimentally determined combustion noise (with 2σ error bars to show cycle-to-cycle variations) for a pilot–main injection strategy with constant CA50 and IMEPg = 9 bar; details of experiments are given in Ref. [18]

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Fig. 2

Top-hat HR profiles used as simulation inputs

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Fig. 3

Simulated combustion noise (computed according to the routine provided in Ref. [27]) for the HR profiles shown in Fig. 2

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Fig. 4

Decomposition of simulated cylinder pressure into individual terms for the combustion-dwell variation

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Fig. 5

Decomposition of Pheat into PHR and Pwall for the variation of combustion dwell

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Fig. 6

Simulated SPLs for the variation of combustion dwell for all dwells shown in Fig. 3. The thick black line represents the spectrum for the minimum noise case.

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Fig. 7

Ramped step functions and pressure signatures representing PHR for the pilot and main HR events for a large (0.54 ms) combustion dwell

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Fig. 8

Ramped step functions and pressure signatures representing PHR for the pilot and main HR events for a short (0.080 ms), noise-minimized combustion dwell

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Fig. 9

Ramped step functions and pressure signatures representing PHR for the pilot and main HR events for zero combustion dwell

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Fig. 10

Ensemble-averaged, measured cylinder pressures with and without band-pass filtering; details of the associated engine experiments are given in Ref. [18]. In this figure, dwell refers to injector-solenoid energizing dwell.

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Fig. 11

Simulated combustion noise for HR profiles shown in Fig. 2; the HR profiles are block shifted to change CA50

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Fig. 12

Combustion noise versus dP/max for HR profiles shown in Fig. 2; the HR profiles are block shifted to change CA50

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Fig. 13

Combustion noise for HR profiles shown in Fig. 2; the pilot HR profile is scaled by a different factor for each curve

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Fig. 14

SPL for the noise-maximized combustion dwell (the dwell is the same for each scaling-factor) shown in Fig. 13

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Fig. 15

Band-pass filtered simulated cylinder pressures for a combustion dwell of 9 CAD and a scaled pilot HR event (see Fig. 13)

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Fig. 17

Combustion noise for the HR profiles shown in Fig. 16

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Fig. 16

HR profiles for the variation in initial main HR rise rate; the rise rate variation is performed separately for each of the three pilot HR profiles

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Fig. 20

Simulated combustion noise for four main HR rise rates (see Fig. 16)

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Fig. 19

Simulated cylinder pressures and band-pass filtered pressure traces for a close-coupled pilot (Fig. 16)

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Fig. 18

Simulated cylinder pressures and band-pass filtered pressure traces for the far pilot case (Fig. 16)

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Fig. 23

Comparison of cylinder pressure traces. The starts of HR events have been adjusted to approximate experimental data.

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Fig. 21

Generic, periodic stepped-ramp waveform P(t)

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Fig. 22

Amplitude and phase shift (unwrapped) characteristics of the FIR band-pass filter

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