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

Effect of Premixed Fuel Preparation for Partially Premixed Combustion With a Low Octane Gasoline on a Light-Duty Multicylinder Compression Ignition Engine

[+] Author and Article Information
Adam B. Dempsey

Oak Ridge National Laboratory,
Fuels, Engines, and Emissions Research Center,
National Transportation Research Center,
2360 Cherahala Boulevard,
Knoxville, TN 37932
e-mail: dempsab@gmail.com

Scott Curran, Robert Wagner

Oak Ridge National Laboratory,
Fuels, Engines, and Emissions Research Center,
National Transportation Research Center,
2360 Cherahala Boulevard,
Knoxville, TN 37932

William Cannella

Chevron Energy Technology Company,
6001 Bollinger Canyon Road,
San Ramon, CA 94583

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 28, 2015; final manuscript received March 25, 2015; published online May 12, 2015. 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 137(11), 111506 (Nov 01, 2015) (12 pages) Paper No: GTP-15-1067; doi: 10.1115/1.4030281 History: Received February 28, 2015; Revised March 25, 2015; Online May 12, 2015

Gasoline compression ignition (GCI) concepts with the majority of the fuel being introduced early in the cycle are known as partially premixed combustion (PPC). Previous research on single- and multicylinder engines has shown that PPC has the potential for high thermal efficiency with low NOx and soot emissions. A variety of fuel injection strategies have been proposed in the literature. These injection strategies aim to create a partially stratified charge to simultaneously reduce NOx and soot emissions while maintaining some level of control over the combustion process through the fuel delivery system. The impact of the direct injection (DI) strategy to create a premixed charge of fuel and air has not previously been explored, and its impact on engine efficiency and emissions is not well understood. This paper explores the effect of sweeping the direct injected pilot timing from −91 deg to −324 deg ATDC, which is just after the exhaust valve closes (EVCs) for the engine used in this study. During the sweep, the pilot injection consistently contained 65% of the total fuel (based on command duration ratio), and the main injection timing was adjusted slightly to maintain combustion phasing near top dead center. A modern four cylinder, 1.9 l diesel engine with a variable geometry turbocharger (VGT), high pressure common rail injection system, wide included angle injectors, and variable swirl actuations was used in this study. The pistons were modified to an open bowl configuration suitable for highly premixed combustion modes. The stock diesel injection system was unmodified, and the gasoline fuel was doped with a lubricity additive to protect the high pressure fuel pump and the injectors. The study was conducted at a fixed speed/load condition of 2000 rpm and 4.0 bar brake mean effective pressure (BMEP). The pilot injection timing sweep was conducted at different intake manifold pressures, swirl levels, and fuel injection pressures. The gasoline used in this study has relatively high fuel reactivity with a research octane number of 68. The results of this experimental campaign indicate that the highest brake thermal efficiency (BTE) and lowest emissions are achieved simultaneously with the earliest pilot injection timings (i.e., during the intake stroke).

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Figures

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Fig. 1

Stock GM 1.9 l piston compared to the modified piston

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Fig. 2

Multicylinder GM 1.9 l engine schematic. The DI injectors are shown on an angle for illustrative purposes but are mounted vertically in the cylinder head.

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Fig. 3

Fuel system configuration for measurement and conditioning for high pressure DI of gasoline

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Fig. 4

Response of combustion phasing (CA50) to changes in the main injection timing for a pilot injection timing of −91 deg ATDC. Base settings: swirl ratio of 2.5, intake pressure of 1.15 bar, and injection pressure of 550 bar.

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Fig. 5

Response of combustion phasing (CA50) to changes in the main injection timing for a pilot injection timing of −324 deg ATDC. Base settings: swirl ratio of 2.5, intake pressure of 1.15 bar, and injection pressure of 550 bar.

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Fig. 6

(Left) Illustration of the relationship between pilot start of injection timings and the intake valve lift. (Right) Injector hole spray axis and piston locations for the pilot injection timings.

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Fig. 7

(Top) Main injection timing and (bottom) combustion phasing (CA50) for cylinder #1 as a function of the pilot injection timing for three different swirl ratios. Base settings: intake pressure of 1.15 bar and injection pressure of 550 bar.

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Fig. 8

Cylinder pressure and AHRR results from cylinder #1 during the pilot injection timing sweep at the baseline settings. Base settings: swirl ratio of 2.5, intake pressure of 1.15 bar, and injection pressure of 550 bar.

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Fig. 9

(Top) BSCO emissions and (bottom) BSHC emissions as a function of the pilot injection timing for three different swirl ratios. Base settings: intake pressure of 1.15 bar and injection pressure of 550 bar.

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Fig. 10

Combustion efficiency as a function of the pilot injection timing for three different swirl ratios. Base settings: intake pressure of 1.15 bar and injection pressure of 550 bar.

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Fig. 11

BSNOx emissions as a function of the pilot injection timing for three different swirl ratios. Base settings: intake pressure of 1.15 bar and injection pressure of 550 bar.

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Fig. 12

BTE as a function of the pilot injection timing for three different swirl ratios. Base settings: intake pressure of 1.15 bar and injection pressure of 550 bar.

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Fig. 13

(Top) BSCO emissions and (bottom) BSHC emissions as a function of the pilot injection timing for three different injection pressures. Base settings: intake pressure of 1.15 bar and swirl ratio of 2.5.

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Fig. 14

Combustion efficiency as a function of the pilot injection timing for three different injection pressures. Base settings: intake pressure of 1.15 bar and swirl ratio of 2.5.

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Fig. 15

BSNOx emissions as a function of the pilot injection timing for three different injection pressures. Base settings: intake pressure of 1.15 bar and swirl ratio of 2.5.

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Fig. 16

BTE as a function of the pilot injection timing for three different injection pressures. Base settings: intake pressure of 1.15 bar and swirl ratio of 2.5.

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Fig. 17

Response of combustion phasing (CA50) to changes in the intake pressure for a pilot injection timing of −324 deg ATDC. Base settings: swirl ratio of 2.5 and injection pressure of 550 bar.

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Fig. 18

(Top) BSCO emissions and (bottom) BSHC emissions as a function of the pilot injection timing for three different intake pressures. Base settings: swirl ratio of 2.5 and injection pressure of 550 bar.

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Fig. 19

Combustion efficiency as a function of the pilot injection timing for three different intake pressures. Base settings: swirl ratio of 2.5 and injection pressure of 550 bar.

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Fig. 20

BSNOx emissions as a function of the pilot injection timing for three different intake pressures. Base settings: swirl ratio of 2.5 and injection pressure of 550 bar.

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Fig. 21

BET as a function of the pilot injection timing for three different intake pressures. Base settings: swirl ratio of 2.5 and injection pressure of 550 bar.

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Fig. 22

Cylinder pressure and AHRR results for all four cylinders at the final operating condition. Settings: swirl ratio of 2.0, intake pressure of 1.05 bar, and injection pressure of 700 bar.

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