Research Papers: Fuel Combustion

High-Speed Rainbow Schlieren Deflectometry of n-Heptane Sprays Using a Common Rail Diesel Injector

[+] Author and Article Information
Eileen M. Mirynowski

Department of Mechanical Engineering,
University of Alabama,
Tuscaloosa, AL 35487
e-mail: emmirynowski@crimson.ua.edu

Ajay K. Agrawal

Department of Mechanical Engineering,
University of Alabama,
Tuscaloosa, AL 35487
e-mail: aagrawal@eng.ua.edu

Joshua A. Bittle

Department of Mechanical Engineering,
University of Alabama,
Tuscaloosa, AL 35487
e-mail: jbittle@eng.ua.edu

1Corresponding author.

Contributed by the Internal Combustion Engine Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received February 22, 2017; final manuscript received April 4, 2017; published online June 27, 2017. Assoc. Editor: Stephen A. Ciatti.

J. Energy Resour. Technol 139(6), 062205 (Jun 27, 2017) (9 pages) Paper No: JERT-17-1092; doi: 10.1115/1.4036959 History: Received February 22, 2017; Revised April 04, 2017

More precise measurements of the fuel injection process can enable better combustion control and more accurate predictions resulting in a reduction of fuel consumption and toxic emissions. Many of the current methods researchers are using to investigate the transient liquid fuel sprays are limited by cross-sensitivity when studying regions with both liquid and vapor phases present (i.e., upstream of the liquid length). The quantitative rainbow schlieren technique has been demonstrated in the past for gaseous fuel jets and is being developed here to enable study of the spray near the injector. In this work, an optically accessible constant pressure flow rig (CPFR) and a modern common rail diesel injector are used to obtain high-speed images of vaporizing fuel sprays at elevated ambient temperatures and pressures. Quantitative results of full-field equivalence ratio measurements are presented as well as more traditional measurements such as vapor penetration and angle for a single condition (13 bar, 180 °C normal air) using n-heptane injected through a single hole (0.1 mm diameter) common rail fuel injector at 1000 bar fuel injection pressure. This work serves as a proof of concept for the rainbow schlieren technique being applied to vaporizing fuel sprays, and full details of the image-processing routine are provided. The ability of the imaging technique combined with the constant pressure flow rig make this approach ideal for generating large data sets in short periods of time for a wide range of operating conditions.

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Fig. 1

Constant pressure flow rig (CPFR) illustration. Fuel is injected axial from left to right with the injector tip just visible in left side of window [14].

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Fig. 2

Rainbow schlieren optical setup schematic showing example deflected light path

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Fig. 3

Sample images of spray showing ensemble averaging processes. Images are 1.5 ms after start of injection prior to reaching quasi-steady conditions.

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Fig. 4

Example screen shots (no postprocessing) used for calibration of distances as a function of hue recorded by the camera. Note: Injector tip is visible on left of image and region used for calibration is highlighted in center.

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Fig. 5

Raw hue calibration data for 2.5 mm symmetric filter as filter is manually traversed through entire width. Error bars represent ±2σ over the region sampled for calibration (outlined in Fig. 4).

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Fig. 6

Flipped and curve fit results of calibration for 2.5 mm filter converting measured hue to deflection distance at the filter. Error bars represent ±2σ over the region sampled for calibration (outlined in Fig. 4).

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Fig. 7

Illustration of light ray deflection geometry (not to scale). The dashed line shows light path if no fuel present and a conceptual path required to get back to focal point; the solid line shows deflected path passing through different color in filter.

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Fig. 8

Contour plots showing transient evolution of center plane equivalence ratio. Region near injector is not resolved due to spatial resolution issues.

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Fig. 10

Axial variation in centerline and cross section average equivalence ratio as well as spray cone angle once the spray has become steady. Only every fifth point is shown to make distinguishing plots simpler.

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Fig. 9

Radial variation in equivalence ratio at various axial locations once the spray has become steady

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Fig. 12

Time evolution in vapor penetration distance

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Fig. 11

Axial variation in centerline and cross section average equivalence ratio as well as spray cone angle at 0.5 ms aSOI. Only every fifth point is shown to make distinguishing plots simpler.



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