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    Exergy loss characteristics of DME/air and ethanol/air mixtures with temperature and concentration fluctuations under HCCI/SCCI conditions: A DNS study

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    Name:
    Zhang et al. - 2020 - Exergy loss characteristics of DMEair and ethanol.pdf
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    4.625Mb
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    PDF
    Description:
    Accepted manuscript
    Embargo End Date:
    2022-12-29
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    Type
    Article
    Authors
    Zhang, Jiabo
    Luong, Minh Bau cc
    Pérez, Francisco E.Hernández
    Han, Dong
    Im, Hong G. cc
    Huang, Zhen
    KAUST Department
    Clean Combustion Research Center
    Computational Reacting Flow Laboratory (CRFL)
    Mechanical Engineering Program
    Physical Science and Engineering (PSE) Division
    Date
    2020-12-29
    Embargo End Date
    2022-12-29
    Submitted Date
    2020-07-20
    Permanent link to this record
    http://hdl.handle.net/10754/666865
    
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    Abstract
    The exergy loss characteristics of combustion processes under homogeneous-charge compression ignition (HCCI) and stratified-charge compression ignition (SCCI) conditions are numerically investigated by analyzing two-dimensional (2-D) direct numerical simulation (DNS) data. Two fuels, dimethyl ether and ethanol, together with the initial conditions of different mean temperatures, and levels of temperature and concentration fluctuations relevant to HCCI/SCCI conditions were investigated. It is found that the prevalent deflagration mode significantly decreases the maximum exergy loss rates and spreads out the exergy loss rate for all the cases regardless of fuel types, temperature regimes, and temperature and/or concentration fluctuations. The primary irreversible sources of exergy loss are also identified. The chemical reaction is found to be the primary contributor to the total exergy loss, followed by heat conduction and mass diffusion, regardless of the fluctuation levels. It is also found that the relative change of exergy loss due to chemical reactions, ELchemrel, correlates strongly with the heat release fraction by deflagration. The maximum ELchemrel is found to be less than 10%. Chemical pathway analysis reveals that the exergy loss induced by low-temperature reactions, represented by the decomposition of hydroperoxy–alkylperoxy and the H-abstraction reactions of the fuel molecule, is much lower under the SCCI conditions than that under the HCCI conditions. Generally, the dominant reactions contributing to the exergy loss in the high-temperature regime are nearly identical for the HCCI and SCCI combustion. Key reactions, including the H2O2 loop reactions, the reactions of the H2–O2 mechanism, and the conversion reaction of CO to CO2, CO+OH=CO2+H, are found to contribute more than 50% of the total exergy loss. Due to locally higher reactivities by temperature and concentration fluctuations inducing deflagration dominance, these reactions occur at a relatively higher temperature (1600 K–1900 K) compared with the homogeneous zero-dimensional cases (∼1400 K), resulting in a net reduction in exergy loss.
    Citation
    Zhang, J., Luong, M. B., Pérez, F. E. H., Han, D., Im, H. G., & Huang, Z. (2021). Exergy loss characteristics of DME/air and ethanol/air mixtures with temperature and concentration fluctuations under HCCI/SCCI conditions: A DNS study. Combustion and Flame, 226, 334–346. doi:10.1016/j.combustflame.2020.12.028
    Sponsors
    The authors would like to thank Prof. Tianfeng Lu for providing the code to leverage between the reduced mechanism and the skeletal mechanism. This work was sponsored by the research funding from King Abdullah University of Science and Technology, and National Natural Science Foundation of China (Grant Nos. 51861135303 and 51776124). This research used the computational resources of the KAUST Supercomputing Laboratory (KSL).
    Publisher
    Elsevier BV
    Journal
    Combustion and Flame
    DOI
    10.1016/j.combustflame.2020.12.028
    Additional Links
    https://linkinghub.elsevier.com/retrieve/pii/S0010218020305770
    ae974a485f413a2113503eed53cd6c53
    10.1016/j.combustflame.2020.12.028
    Scopus Count
    Collections
    Articles; Physical Science and Engineering (PSE) Division; Mechanical Engineering Program; Clean Combustion Research Center

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