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MILD combustion versus conventional bluff-body flame of a premixed CH4/air jet in hot coflow

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  • Wang, G.
  • Si, J.
  • Xu, M.
  • Mi, J.

Abstract

The present work is to investigate the MILD (moderate and intense low-oxygen dilution) combustion of a premixed methane jet in hot coflow against its conventional counterpart, i.e., a typical bluff-body flame, under identical inlet and boundary conditions. This paper demonstrates that the MILD combustion develops as a stable ‘flame’ lifting far downstream from the nozzle while the conventional flame evolves immediately behind the bluff body. More specifically, all chemical reactions are found to occur far more slowly over a greatly larger reaction zone for the MILD combustion than for the conventional one. Also, for the MILD combustion, the laminar flame speed (SL) is very small, far below the local flow speed (Ux), whereas chemical and mixing times are compatible so that the Damköhler number Da ∼1.0. In contrast, the conventional combustion takes place with SL ≥ Ux and Da = 10–1000. Moreover, the MILD combustion eventually emits little NOx, only less than 3% of the emission from the conventional counterpart. Fundamentally, the MILD combustion produces the NOx emission mainly through the N2O-intermediate and NNH routes while the thermal NOx mechanism dominates the conventional flame. In addition, this paper provides a comprehensive explanation to each of the above differences.

Suggested Citation

  • Wang, G. & Si, J. & Xu, M. & Mi, J., 2019. "MILD combustion versus conventional bluff-body flame of a premixed CH4/air jet in hot coflow," Energy, Elsevier, vol. 187(C).
    • Handle: RePEc:eee:energy:v:187:y:2019:i:c:s0360544219316184
    DOI: 10.1016/j.energy.2019.115934
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    References listed on IDEAS

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    1. Mi, Jianchun & Li, Pengfei & Zheng, Chuguang, 2011. "Impact of injection conditions on flame characteristics from a parallel multi-jet burner," Energy, Elsevier, vol. 36(11), pages 6583-6595.
    2. Cheong, Kin-Pang & Li, Pengfei & Wang, Feifei & Mi, Jianchun, 2017. "Emissions of NO and CO from counterflow combustion of CH4 under MILD and oxyfuel conditions," Energy, Elsevier, vol. 124(C), pages 652-664.
    3. Kruse, Stephan & Kerschgens, Bruno & Berger, Lukas & Varea, Emilien & Pitsch, Heinz, 2015. "Experimental and numerical study of MILD combustion for gas turbine applications," Applied Energy, Elsevier, vol. 148(C), pages 456-465.
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    2. Orati, Edson & Veríssimo, Anton S. & Rocha, Ana Maura A. & Costa, Fernando S. & Carvalho, João A., 2022. "Experimental investigation of flameless combustion of biodiesel," Energy, Elsevier, vol. 255(C).
    3. Zhao, Zhenghong & Zhang, Zewu & Zha, Xiaojian & Gao, Ge & Li, Xiaoshan & Wu, Fan & Luo, Cong & Zhang, Liqi, 2023. "Internal association between combustion behavior and NOx emissions of pulverized coal MILD-oxy combustion affected by adding H2O," Energy, Elsevier, vol. 263(PD).
    4. Fordoei, Esmaeil Ebrahimi & Boyaghchi, Fateme Ahmadi, 2022. "Influence of wall thermal conditions on the ignition, flame structure, and temperature behaviors in air-fuel, oxygen-enhanced, and oxy-fuel combustion under the MILD and high-temperature regimes," Energy, Elsevier, vol. 255(C).
    5. Shaker, Ahmad & Fordoei, E. Ebrahimi & Boyaghchi, Fateme Ahmadi, 2023. "Study of NO emission from CH4-air, oxygen-enriched, and oxy-CH4 combustion under HTC and MILD regimes: Impact of wall thermal condition in different oxidant temperature and dilution level," Energy, Elsevier, vol. 277(C).
    6. Ren, Shoujun & Yang, Haolin & Wang, Xiaohan, 2021. "The oxygen-deficient combustion and its effect on the NOx emission in a localized stratified vortex-tube combustor," Energy, Elsevier, vol. 235(C).

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