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Research Papers: Internal Combustion Engines

Tailoring Charge Reactivity Using In-Cylinder Generated Reformate for Gasoline Compression Ignition Strategies

[+] Author and Article Information
Isaac W. Ekoto

Sandia National Laboratories,
7011 East Vasco,
Livermore, CA 94551
e-mail: iekoto@sandia.gov

Benjamin M. Wolk

Tula Technology, Inc.,
2460 Zanker Road,
San Jose, CA 95131
e-mail: wolkb@tulatech.com

William F. Northrop

University of Minnesota,
Twin Cities,
Minneapolis, MN 55455
e-mail: wnorthro@umn.edu

Nils Hansen

Sandia National Laboratories,
7011 East Vasco,
Livermore, CA 94551
e-mail: nhansen@sandia.gov

Kai Moshammer

PTB Physikalisch-Technische Bundesanstalt
Braunschweig und Berlin,
Bundesallee 100,
Braunschweig 38116, Germany
e-mail: kai.moshammer@ptb.de

Contributed by the IC Engine Division of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received February 22, 2017; final manuscript received May 8, 2017; published online August 9, 2017. 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 nonexclusive, 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 139(12), 122801 (Aug 09, 2017) (10 pages) Paper No: GTP-17-1078; doi: 10.1115/1.4037207 History: Received February 22, 2017; Revised May 08, 2017

In-cylinder reforming of injected fuel during a negative valve overlap (NVO) recompression period can be used to optimize main-cycle combustion phasing for low-load low-temperature gasoline combustion (LTGC). The objective of this work is to examine the effects of reformate composition on main-cycle engine performance. An alternate-fire sequence was used to generate a common exhaust temperature and composition boundary condition for a cycle-of-interest, with performance metrics measured for these custom cycles. NVO reformate was also separately collected using a dump-valve apparatus and characterized by both gas chromatography (GC) and photoionization mass spectroscopy (PIMS). To facilitate gas sample analysis, sampling experiments were conducted using a five-component gasoline surrogate (iso-octane, n-heptane, ethanol, 1-hexene, and toluene) that matched the molecular composition, 50% boiling point, and ignition characteristics of the research gasoline. For the gasoline, it was found that an advance of the NVO start-of-injection (SOI) led to a corresponding advance in main-period combustion phasing as the combination of longer residence times and lower amounts of liquid spray piston impingement led to a greater degree of fuel decomposition. The effect was more pronounced as the fraction of total fuel injected in the NVO period increased. Main-period combustion phasing was also found to advance as the main-period fueling decreased. Slower kinetics for leaner mixtures were offset by a combination of increased bulk-gas temperature from higher charge specific heat ratios and increased fuel reactivity due to higher charge reformate fractions.

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Figures

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Fig. 1

Dump-sample collection sequence illustration

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Fig. 2

Main-period ensemble-averaged AHRR profiles for a cycle-of-interest (−65 CANVO SOI; 400 J/cycle) along with preconditioning and target-cycle preconditioning profiles

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Fig. 3

GC speciation results (left) broken down into surrogate fuel components, H2, and by carbon number as a fraction of NVO injection fuel energy for SOI = −65, −40, and −10 CANVO. The NVO-period AHR is also shown (right).

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Fig. 4

Main-period ensemble-averaged AHRR profiles for a sweep of NVO SOI with fixed NVO injection rates (265 J) and the engine fueled by RD587 gasoline (dashed) or the surrogate (solid)

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Fig. 5

ITE (top), CoV of IMEP (middle), and main-period CA10 (bottom) as a function of total cycle fuel energy and NVO SOI for the RD587 gasoline with NVO injected fuel energy fixed at 265 J

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Fig. 6

ITE (top), CoV of IMEP (middle), and main-period CA10 (bottom) as a function of total cycle fuel energy and NVO SOI for the RD587 surrogate with NVO injected fuel energy fixed at 265 J

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Fig. 7

Main-period CA10 for the RD587 gasoline (open symbols) and surrogate (filled symbols) as a function of NVO SOI for 400 J (triangles) and 600 J (squares) total injected fuel quantities

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Fig. 8

Main-period ensemble-averaged AHRR profiles for a sweep of NVO injection rates with fixed SOI (−40 CANVO) and the engine fueled by RD587 gasoline (dashed) or the surrogate (solid)

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Fig. 9

ITE (top), CoV of IMEP (middle), and main-period CA10 (bottom) as a function of the total cycle and NVO fuel injected for the RD587 gasoline with NVO SOI = −40 CANVO

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Fig. 10

ITE (top), CoV of IMEP (middle), and main-period CA10 (bottom) as a function of the total cycle and NVO fuel injected for the RD587 surrogate with NVO SOI = −40 CANVO

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Fig. 11

Main-period CA10 for the RD587 gasoline (open symbols) and surrogate (filled symbols) as a function of NVO injected fuel energy for 400 J (circles) and 600 J (diamonds) total injected fuel quantities

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Fig. 12

Auto-ignition delay time for mixtures of reformate and parent fuel at 850 K, 15 bar (solid lines, left y-axis) and 950 K, 22 bar (dashed lines, right y-axis)

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Fig. 13

Estimated temperature at −20 CA and γ during compression for the RD587 surrogate and PIMS-measured reformate

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Fig. 14

tign at 15 bar for the RD587 surrogate and PIMS-measured reformate for 400, 600, and 700 J of total fuel energy using the GC-measured oxidizer stream (9.5% O2, 4.8% CO2, 4.9% H2O, and 80.8% N2)

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