Towards the development of an efficient low-NOx ammonia combustor for a micro gas turbine

Ekenechukwu C. Okafor, K. D.Kunkuma A. Somarathne, Akihiro Hayakawa, Taku Kudo, Osamu Kurata, Norihiko Iki, Hideaki Kobayashi

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Recent studies have demonstrated stable generation of power from pure ammonia combustion in a micro gas turbine (MGT) with a high combustion efficiency, thus overcoming some of the challenges that discouraged such applications of ammonia in the past. However, achievement of low NOx emission from ammonia combustors remains an important challenge. In this study, combustion techniques and combustor design for efficient combustion and low NOx emission from an ammonia MGT swirl combustor are proposed. The effects of fuel injection angle, combustor inlet temperature, equivalence ratio, and ambient pressure on flame stabilization and emissions were investigated in a laboratory high pressure combustion chamber. An FTIR gas analyser was employed in analysing the exhaust gases. Numerical modeling using OpenFOAM was done to better understand the dependence of NO emissions on the equivalence ratio. The result show that inclined fuel injection as opposed to vertical injection along the combustor central axis resulted to improved flame stability, and lower NH 3 and NOx emissions. Numerical and experimental results showed that a control of the equivalence ratio upstream of the combustor is critical for low NOx emission in a rich-lean ammonia combustor. NO emission had a minimum value at an upstream equivalence ratio of 1.10 in the experiments. Furthermore, NO emission was found to decrease with ambient pressure, especially for premixed combustion. For the rich-lean combustion strategy employed in this study, lower NOx emission was recorded in premixed combustion than in non-premixed combustion indicating the importance of mixture uniformity for low NOx emission from ammonia combustion. A prototype liner developed to enhance the control and uniformity of the equivalence ratio upstream of the combustor further improved ammonia combustion. With the proposed liner design, NOx emission of 42ppmv and ammonia combustion efficiency of 99.5% were achieved at 0.3MPa for fuel input power of 31.44kW.

Original languageEnglish
Pages (from-to)4597-4606
Number of pages10
JournalProceedings of the Combustion Institute
Volume37
Issue number4
DOIs
Publication statusPublished - 2019 Jan 1

Keywords

  • Ammonia
  • Carbon-free fuel
  • Gas turbine
  • Low-NOx combustor

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Mechanical Engineering
  • Physical and Theoretical Chemistry

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