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Research Papers: Fuel Combustion

A Comparison of Methyl Decanoate and Tripropylene Glycol Monomethyl Ether for Soot-Free Combustion in an Optical Direct-Injection Diesel Engine

[+] Author and Article Information
Cosmin E. Dumitrescu

Department of Mechanical
and Aerospace Engineering,
West Virginia University,
275 Engineering Science Building,
Morgantown, WV 26506
e-mail: cosmin.dumitrescu@mail.wvu.edu

A. S. Cheng

School of Engineering,
San Francisco State University,
1600 Holloway Avenue,
San Francisco, CA 94132
e-mail: ascheng@sfsu.edu

Eric Kurtz

Ford Motor Co.,
1 American Road,
Dearborn, MI 48126
e-mail: ekurtz@ford.com

Charles J. Mueller

Sandia National Laboratories,
7011 East Avenue,
Livermore, CA 94550
e-mail: cjmuell@sandia.gov

1Corresponding author.

Contributed by the Internal Combustion Engine Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received February 20, 2017; final manuscript received February 27, 2017; published online April 10, 2017. Assoc. Editor: Stephen A. Ciatti.

J. Energy Resour. Technol 139(4), 042210 (Apr 10, 2017) (13 pages) Paper No: JERT-17-1087; doi: 10.1115/1.4036330 History: Received February 20, 2017; Revised February 27, 2017

Oxygenated fuels have beneficial effects for leaner lifted-flame combustion (LLFC), a nonsooting mode of mixing-controlled combustion associated with lift-off length equivalence ratios below approximately 2. A single-cylinder heavy-duty optical compression-ignition engine was used to compare neat methyl decanoate (MD) and T50, a 50/50 blend by volume of tripropylene glycol monomethyl ether (TPGME) and #2 ultralow sulfur emissions-certification diesel fuel (CF). High-speed, simultaneous imaging of natural luminosity (NL) and chemiluminescence (CL) were employed to investigate the ignition, combustion, and soot formation/oxidation processes at two injection pressures and three dilution levels. Additional Mie scattering measurements observed fuel-property effects on the liquid length of the injected spray. Results indicate that both MD and T50 effectively eliminated engine-out smoke emissions by decreasing soot formation and increasing soot oxidation during and after the end of fuel injection. MD further reduced soot emissions by 50–90% compared with T50, because TPGME could not completely compensate for the aromatics in the CF. Despite the low engine-out soot emissions, both fuels produced in-cylinder soot because the equivalence ratio at the lift-off length never reached the nonsooting limit. With respect to the other engine-out emissions, T50 had up to 16% higher nitrogen oxides (NOx) emissions compared with MD, but neither fuel showed the traditional soot-NOx trade-off associated with conventional mixing-controlled combustion. In addition, T50 had up to 15% and 26% lower unburned hydrocarbons (HC) and CO emissions, respectively, compared with MD.

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References

Figures

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Fig. 1

Optical engine schematic. Intensified and nonintensified cameras are used for chemiluminescence and natural luminosity, respectively.

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Fig. 2

MD and T50 injection-rate profiles

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Fig. 3

Molecular structure of one isomer of tripropylene glycol monomethyl ether (C10H22O4) and methyl decanoate (C11H22O2)

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Fig. 4

Schematics of the optical-engine imaging setup as configured for measuring liquid length. The cutaway overview (a) shows how a laser sheet is directed via the piston mirror through the piston window into the combustion chamber and is aligned with the plane of the fuel jets. The close-up view (b) shows how a notch in the piston bowl-rim enables optical access to the piston bowl when the piston is near TDC.

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Fig. 5

Effect of fuel, injection pressure, and intake O2 concentration on exhaust-LII intensity and filter smoke number (top row), and the relative reduction in smoke emissions of MD relative to T50 (bottom row). The error bars represent the minimum and maximum average values on three separate optical-engine runs.

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Fig. 6

Apparent heat release rate (AHRR) for 80-MPa and 180-MPa injection pressure cases

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Fig. 7

Liquid length under noncombusting conditions for 80-MPa and 180-MPa injection pressure cases

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Fig. 8

NL (left column) and CL (right column) images for MD at 18% XO2 and 80-MPa fuel-injection pressure. The dot in the center of each image and the circular border denote the injector tip and piston bowl-rim, respectively. Values shown on each image frame are (clockwise from top-left): CAD after TDC, fired-cycle number, image number, and time after start of injection.

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Fig. 9

Sample instantaneous and simultaneous overlaid NL and CL images acquired at different crank angles during the combustion process, for 18 mol % O2 charge dilution and at 80- and 180 MPa fuel injection pressure. The fuel in each row of images is indicated on the left-most image of the row. See text for details regarding the different areas and lines shown in the figure. Also shown on each image frame are (clockwise from top-left): CAD after TDC, fired-cycle number, image number, and time after start of injection.

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Fig. 10

Spatially integrated natural luminosity (SINL)

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Fig. 11

Effect of fuel on the SINL level at similar operating conditions (a) and effect of injection pressure on SINL level at similar dilution level (b)

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Fig. 12

Effect of fuel, injection pressure, and intake-O2 concentration on H and the equivalence ratio at H, ϕ(H)

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Fig. 13

Effect of fuel, injection pressure, and intake-O2 concentration on NOx emissions (top row), and the relative increase in NOx emissions of T50 relative to MD (bottom row). NOx emissions for MD at both injection pressures are nearly identical and thus appear as a single trendline. The error bars represent the minimum and maximum average values on three separate optical-engine runs.

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Fig. 14

Effect of fuel, injection pressure, and intake-O2 concentration on HC and CO emissions (top row), and the relative decrease in HC and CO emissions of T50 relative to MD (bottom row). The error bars represent the minimum and maximum average values on three separate optical-engine runs.

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