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Research Papers: Internal Combustion Engines

Optical Diagnostics of Late-Injection Low-Temperature Combustion in a Heavy-Duty Diesel Engine

[+] Author and Article Information
Thierry Lachaux

 Sandia National Laboratories, P.O. 969, MS9053, Livermore, CA 94551

Mark P. Musculus

 Sandia National Laboratories, P.O. 969, MS9053, Livermore, CA 94551mpmuscu@sandia.gov

Satbir Singh

Powertrain Systems Research Laboratory,  General Motors Research and Development, Warren, MI 48090

Rolf D. Reitz

Engine Research Center, Department of Mechanical Engineering, The University of Wisconsin, Madison, 1500 Engineering Drive, Madison, WI 53706

J. Eng. Gas Turbines Power 130(3), 032808 (Apr 02, 2008) (9 pages) doi:10.1115/1.2830864 History: Received October 23, 2007; Revised October 24, 2007; Published April 02, 2008

A late-injection, high exhaust-gas recirculation rate, low-temperature combustion strategy is investigated in a heavy-duty diesel engine using a suite of optical diagnostics: chemiluminescence for visualization of ignition and combustion, laser Mie scattering for liquid-fuel imaging, planar laser-induced fluorescence (PLIF) for both OH and vapor-fuel imagings, and laser-induced incandescence for soot imaging. Fuel is injected at top dead center when the in-cylinder gases are hot and dense. Consequently, the maximum liquid-fuel penetration is 27 mm, which is short enough to avoid wall impingement. The cool flame starts 4.5 crank angle degrees (CAD) after the start of injection (ASI), midway between the injector and bowl rim, and likely helps fuel to vaporize. Within a few CAD, the cool-flame combustion reaches the bowl rim. A large premixed combustion occurs near 9 CAD ASI, close to the bowl rim. Soot is visible shortly afterward, along the walls, typically between two adjacent jets. OH PLIF indicates that premixed combustion first occurs within the jet and then spreads along the bowl rim in a thin layer, surrounding soot pockets at the start of the mixing-controlled combustion phase near 17 CAD ASI. During the mixing-controlled phase, soot is not fully oxidized and is still present near the bowl rim late in the cycle. At the end of combustion near 27 CAD ASI, averaged PLIF images indicate two separate zones. OH PLIF appears near the bowl rim, while broadband PLIF persists late in the cycle near the injector. The most likely source of broadband PLIF is unburned fuel, which indicates that the near-injector region is a potential source of unburned hydrocarbons.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Engine cross-section schematic and optical diagnostics setup and field of view from the piston window (inset)

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Figure 2

Mass rate of injection and APHR. The boxed numbers 1, 2, and 3 represent the cool-flame phase, the premixed-combustion phase, and the mixing-controlled phase, respectively

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Figure 3

Liquid-phase (LMS, blue) and vapor-phase (BB-PLIF, green) fuels. The crankshaft angle is displayed on the top left corner and the LMS and BB-PLIF gains are on the bottom of each image. The small white dot marks the injector location and the thick white line indicates the location of bowl rim, 50mm from the injector.

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Figure 4

Liquid length extracted from the LMS instantaneous images

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Figure 5

Chemiluminescence averaged pictures. The crank angle is displayed on the top left corner while the relative gain is displayed at the bottom left corner. The small white dot marks the injector location and the thick white line indicates the location of bowl rim, 50mm from the injector.

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Figure 6

Natural luminosity intensity, plotted (a) along the jet centerline and (b) averaged along the centerline

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Figure 7

Instantaneous images from fuel and OH fluorescence (green) and laser-induced incandescence (red). The crank angle is displayed at the top left corner of the picture while the relative gains are displayed at the bottom. The small white dot marks the injector location and the thick white line indicates the location of bowl rim, 50mm from the injector. The vertical dashed line indicates the approximate separation of fluorescence from OH, on the right, and broadband sources (e.g., fuel), on the left.

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Figure 8

On-line (red) and off-line (green) ensemble-averaged OH-PLIF images. The crank angle is displayed on the top left corner while the relative gains are displayed on the bottom. The small white dot marks the injector location and the thick white line indicates the location of bowl rim, 50mm from the injector.

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Figure 9

Instantaneous images of simultaneous OH fluorescence (green) and chemiluminescence and∕or soot luminosity (red). Annotation is same as for Fig. 7.

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