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Internal Combustion Engines

Soot Evolution With Cyclic Crank-Angle-Resolved Two-Color Thermometry in an Optical Diesel Engine Fueled With Biodiesel Blend and ULSD

[+] Author and Article Information
Kan Zha, Radu-Catalin Florea, Marcis Jansons

 Wayne State University, Detroit, MI 48202

J. Eng. Gas Turbines Power 134(9), 092803 (Jul 18, 2012) (7 pages) doi:10.1115/1.4006710 History: Received November 19, 2011; Revised November 21, 2011; Published July 17, 2012; Online July 18, 2012

Biodiesel is a desirable alternative fuel for the diesel engine due to its low engine-out soot emission tendency. When blended with petroleum-based diesel fuels, soot emissions generally decrease in proportion to the volume fraction of biodiesel in the mixture. While comparisons of engine-out soot measurements between biodiesel blends and petroleum-based diesel have been widely reported, in-cylinder soot evolution has not been experimentally explored to the same extent. To elucidate the soot emission reduction mechanism of biodiesel, a single-cylinder optically-accessible diesel engine was used to compare the in-cylinder soot evolution when fueled with ultra-low sulfur diesel (ULSD) to that using a B20 biodiesel blend (20% vol./vol. biodiesel ASTM D6751-03A). Soot temperature and KL factors are simultaneously determined using a novel two-color optical thermometry technique implemented with a high-speed CMOS color camera having wide-band Bayer filters. The crank-angle resolved data allows quantitative comparison of the rate of in-cylinder soot formation. High-speed spray images show that B20 has more splashing during spray wall impingement than ULSD, distributing rebounding fuel droplets over a thicker annular ring interior to the piston bowl periphery. The subsequent soot luminescence is observed by high-speed combustion imaging and soot temperature and KL factor measurements. B20 forms soot both at low KL magnitudes over large areas between fuel jets, and at high values among remnants of the fuel spray, along its axis and away from the bowl edge. In contrast, ULSD soot luminescence is observed exclusively as pool burning on the piston bowl surfaces resulting from spray wall impingement. The soot KL factor evolution during B20 combustion indicates earlier and significantly greater soot formation than with ULSD. B20 combustion is also observed to have a greater soot oxidation rate, which results in lower late-cycle soot emissions. For both fuels, higher fuel injection pressure led to lower late-cycle soot KL levels. The apparent rate of heat release (ARHR) analysis under steady skip-fire conditions indicates that B20 combustion is less sensitive to wall temperature than that observed with ULSD due to a lesser degree of pool burning. B20 was found to have both a shorter ignition delay and shorter combustion duration than ULSD.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental setup

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Figure 2

Relative error percentage and absolute error between two-color method and measured black body temperature

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Figure 3

Averaged firing cycles for ULSD under a command injection pressure of 800 bars and gathered in three-fire/nine-skip pattern

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Figure 4

Averaged firing cycles for ULSD and B20 under an injection pressure of 800 bars

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Figure 5

Mass burn fraction of the averaged second firing cycles for ULSD and B20 under an injection pressure of 800 bars

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Figure 6

Crank-angle-resolved spray images between ULSD and B20 under an injection pressure of 800 bars, which shows splash height is higher for B20 than ULSD, shown in dashed red oval regions

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Figure 7

Spatial, crank-angle-resolved soot luminosity images from a single engine cycle, calculated soot temperature and KL factor under command injection pressure at 600 bars during start sequence

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Figure 8

Comparison of mean soot temperature and KL evolution of diesel engine cycles using ULSD and B20 fuels. Dashed lines represent total areas of the imaged zone for which solutions were obtained. Calculations are based on the images of Fig. 7.

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Figure 9

ARHR, needle lift, and soot KL summation comparison of two cycles shown in Fig. 7

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Figure 10

Summation of KL for each fuel under 400 bars, 600 bars, and 800 bars

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