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Characterization of the Structure of Turbulent Non-premixed Dimethyl Ether Jet Flames

Shen, Han
http://rave.ohiolink.edu/etdc/view?acc_num=osu1431017181

Abstract Details

2015, Master of Science, Ohio State University, Mechanical Engineering.
Dimethyl ether (DME) is a promising alternative to diesel fuel in compression-ignition engines and a possible substitute to natural gas in power-production applications. However, little is known about the fundamental combustion processes of DME-fueled systems under highly turbulent conditions. In this thesis, laser-based measurements are conducted to achieve a better understanding of DME combustion with a primary focus on the underlying flame structure. In a first set of measurements, the flame structure of turbulent DME flames is examined using hydroxyl (OH) planar laser-induced fluorescence (PLIF) imaging and compared and contrasted to well-characterized CH4 flames operating under nearly identical conditions. The reactive OH layer structure of the CH4- and DME-based turbulent non-premixed jet flame systems are investigated at equivalent Reynolds numbers and equivalent Damkohler numbers to better understand turbulence-chemistry interaction when using DME as a fuel. The results indicate notable differences in the visual structure of the OH fields. For example, the DME-based flames are less wrinkled and contorted and appear to be more “laminar like” over the full range of operating conditions. From the OH PLIF imaging, a detailed set of statistics are derived for each flame system including OH layer thickness, OH layer curvature, OH layer orientation, OH layer surface area, and number of OH layer “holes”. For equivalent Reynolds number conditions, the OH PLIF layers within the DLR flames are much more affected by the turbulence as indicated by a broader statistical distributions in all topological parameters and display a significantly higher level of local extinction than the DME flames as indicated by OH layer “holes”. For equivalent Damkohler numbers, the flame structure statistics of the DME flames are very similar to the DLR flames except for the degree of local extinction, where the DME flames are much less prone to OH layer breakage. These results indicate that DME flames appear to be affected less by the local turbulence than the DLR flames which may be due to more active low-temperature chemistry in the DME flames. The second set of experimental results is derived from a research collaboration with Sandia National Laboratories to compare direct numerical simulation (DNS) of a temporally-evolving jet flame with experimental measurements from a spatially-evolving jet flame operating under identical Reynolds and Damkohler numbers with significant levels of local flame extinction. Simultaneous OH/CH2O (formaldehyde) PLIF imaging is performed to characterize the spatial structure of the turbulent DME flames, where the OH PLIF imaging yields information regarding the high-temperature reactive layer structure and the CH2O PLIF imaging yields information regarding the low-temperature, partial oxidation structure. First, the structure of the flames is in qualitative agreement, displaying similar extinction and re-ignition patterns in both the DNS and the experiments. Joint OH/CH2O statistics from the DNS and the experiments are found to agree very well indicating a strong anti-correlation between OH and CH2O. As one example, an alignment index defined in terms of the OH and CH2O gradients was computed from both DNS and experimental results. For both DNS and experimental results, the probability density function (PDF) of the alignment index peaked at -1 at all time (DNS) and spatial (experiments) instances, indicating that the gradients of OH and CH2O are opposed, even under very low Damkohler number conditions. Finally, the [OH] x [CH2O] product imaging is evaluated as a surrogate for peak heat release rate and is found to be an excellent surrogate of the peak heat release rate in the DNS results. This agreed qualitatively with observed experimental results that showed that the OH and CH2O PLIF images overlapped only in very small spatial regions, presumably demarcating the regions between fuel oxidation and primary heat release. This result is consistent with the statistical results of the alignment index that indicate that the OH and CH2O gradients are opposed, i.e., as CH2O is consumed, OH is formed. The OH/CH2O product imaging which is used to predict peak hear release rate agrees with the simulation extremely well.
Jeffrey Sutton (Advisor)
Seung Hyun Kim (Committee Member)
80 p.
Mechanical Engineering
Dimethyl ether, combustion, turbulent, laser diagnostics

Recommended Citations

Citations

  • Shen, H. (2015). Characterization of the Structure of Turbulent Non-premixed Dimethyl Ether Jet Flames [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1431017181

    APA Style (7th edition)

  • Shen, Han. Characterization of the Structure of Turbulent Non-premixed Dimethyl Ether Jet Flames. 2015. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1431017181.

    MLA Style (8th edition)

  • Shen, Han. "Characterization of the Structure of Turbulent Non-premixed Dimethyl Ether Jet Flames." Master's thesis, Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1431017181

    Chicago Manual of Style (17th edition)

osu1431017181
859
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This open access ETD is published by The Ohio State University and OhioLINK.