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

Investigation of the Effect of Injection and Control Strategies on Combustion Instability in Reactivity-Controlled Compression Ignition Engines

[+] Author and Article Information
David T. Klos

Engine Research Center,
University of Wisconsin-Madison,
Madison, WI 53706
e-mail: dklos@wisc.edu

Sage L. Kokjohn

Engine Research Center,
University of Wisconsin-Madison,
Madison, WI 53706
e-mail: kokjohn@wisc.edu

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received May 19, 2015; final manuscript received July 28, 2015; published online August 18, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(1), 011502 (Aug 18, 2015) (9 pages) Paper No: GTP-15-1173; doi: 10.1115/1.4031179 History: Received May 19, 2015; Revised July 28, 2015

This paper uses detailed computational fluid dynamics (CFD) modeling with the kiva-chemkin code to investigate the influence of injection timing, combustion phasing, and operating conditions on combustion instability. Using detailed CFD simulations, a large design of experiments (DOE) is performed with small perturbations in the intake and fueling conditions. A response surface model (RSM) is then fit to the DOE results to predict cycle-to-cycle combustion instability. Injection timing had significant tradeoffs between engine efficiency, emissions, and combustion instability. Near top dead center (TDC) injection timing can significantly reduce combustion instability, but the emissions and efficiency drop close to conventional diesel combustion levels. The fuel split between the two direct injection (DI) injections has very little effect on combustion instability. Increasing exhaust gas recirculation (EGR) rate, while making adjustments to maintain combustion phasing, can significantly reduce peak pressure rise rate (PPRR) variation until the engine is on the verge of misfiring. Combustion phasing has a very large impact on combustion instability. More advanced phasing is much more stable, but produces high PPRRs, higher NOx levels, and can be less efficient due to increased heat transfer losses. The results of this study identify operating parameters that can significantly improve the combustion stability of dual-fuel reactivity-controlled compression ignition (RCCI) engines.

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References

Figures

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Fig. 1

Comparison of measured and predicted cylinder pressure and AHRR for RCCI combustion. The numbers on plot show gasoline percentages (by mass) ranging from 82% to 89%. The experiments are from Hanson et al. [6].

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Fig. 2

Comparison of measured and predicted GIE, NOx, and soot emissions for RCCI combustion over a gasoline percentage sweep from 82% to 89%. The experiments are from Hanson et al. [6].

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Fig. 3

RSM-predicted output to CFD output

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Fig. 4

Full factorial RSM-predicted outputs to the LHS CFD output

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Fig. 5

Comparison of measured and RSM-predicted results for RCCI combustion using the standard deviation shown in Table 4

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Fig. 6

Predicted variation of IMEP, CA50, GIE, and PPRR as a function of injection timing for a single injection strategy (top) and a double injection strategy (bottom)

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Fig. 7

Predicted average values of IMEP, CA50, GIE, and PPRR as a function of injection timing for a single injection strategy (top) and a double injection strategy (bottom)

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Fig. 8

Average heat loss percent at different injection timings for a single and double injection strategies

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Fig. 9

Predicted variation (top) and average values (bottom) as a function of injection timing from −20 to −10 deg ATDC for a single injection strategy

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Fig. 10

Constant-volume ignition delay calculations illustrating the effect of equivalence ratio and PRF number on ignition delay [11]

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Fig. 11

Predicted variation of IMEP, CA50, and PPRR at different fuel mass splits for double injection

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Fig. 12

Predicted cycle average PPRR at different fuel mass splits

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Fig. 13

Predicted variation of IMEP, CA50, PPRR, and GIE as a function of combustion phasing

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Fig. 14

Predicted average value of IMEP, PPRR, and EICO as a function of combustion phasing

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Fig. 15

PPRR COV as a function of combustion phasing

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