2024/11/28 更新

写真a

オカフオー　エケネチユク　チジオケ
OKAFOR EKENECHUKWU CHIJIOKE
OKAFOR CHIJIOKE EKENECHUKWU
所属
工学研究院 機械工学部門 准教授
工学部 機械工学科（併任）
工学府 機械工学専攻（併任）
職名
准教授
連絡先
メールアドレス
電話番号
0928023147
ホームページ
外部リンク

学位

  • 工学博士　（九州大学、日本） （ 2015年9月   九州大学 ）

経歴

  • 九州大学 准教授

    2022年1月 - 現在

  • 産業技術総合研究所 客員研究員

    2022年1月 - 現在

    　 詳細を見る

  • 産業技術総合研究所 研究員

    2019年4月 - 2021年12月

  • 東北大学 研究員

    2015年10月 - 2019年3月

研究テーマ・研究キーワード

  • 研究テーマ：液体アンモニア噴霧特性解明に関する研究

    研究キーワード：噴霧、液体アンモニア、機械学習

    研究期間： 2024年3月 - 2027年3月

  • 研究テーマ：旋回流燃焼器におけるアンモニア・水素希薄火炎の排気ガス制御方法解明

    研究キーワード：燃焼、水素、アンモニア、保炎、ガスタービン、エミッション、

    研究期間： 2023年4月 - 2025年3月

  • 研究テーマ：酸素富化アンモニア火炎の層流及び乱流燃焼速度解明に関する研究

    研究キーワード：アンモニア、酸素富化燃焼、燃焼速度、

    研究期間： 2022年4月 - 2023年3月

  • 研究テーマ：アンモニア・天然ガス工業炉バーナー研究開発

    研究キーワード：工業炉、バーナー、アンモニア、天然ガス

    研究期間： 2022年4月

  • 研究テーマ：液体アンモニア噴霧燃焼ガスタービン技術研究開発

    研究キーワード：噴霧燃焼、液体アンモニア、ガスタービン、スワールバーナー、エミッション、

    研究期間： 2019年4月 - 2025年9月

  • 研究テーマ：アンモニア燃焼反応モデル構築・検証に関する研究

    研究キーワード：燃焼、アンモニア、反応機構、層流燃焼速度

    研究期間： 2015年10月 - 2019年3月

  • 研究テーマ：旋回流燃焼器におけるアンモニア直接燃焼に関する研究

    研究キーワード：燃焼、アンモニア、保炎、ガスタービン、スワールバーナー、エミッション、

    研究期間： 2015年10月 - 2019年3月

  • 研究テーマ：球状伝播CH4-H2-空気火炎の層流および乱流燃焼速度に及ぼす圧力および水素濃度の影響に関する研究。

    研究キーワード：燃焼、水素、メタン、燃焼速度、Markstein長さ、Markstein数, 火炎伸長, Lewis数

    研究期間： 2010年10月 - 2015年9月

受賞

  • 2023年度　日本燃焼学会　論文賞

    2023年11月   日本燃焼学会  

    　詳細を見る

    In this study, we investigated the effect of pressure on the characteristics of spherically propagating ammonia-methane-air premixed flames. A reduced reaction mechanism was developed based on the detailed reaction model developed in our previous study and optimized for conditions up to 0.5 MPa. At the time of this study, ammonia was beginning to attract attention again as a fuel, and there was a need to develop chemical reaction models for co-combustion of ammonia and hydrocarbons, however there were few measured data on ammonia flame properties under high pressure, which was necessary for optimization of the reaction models. In this study, the laminar burning velocity and Markstein length of ammonia-methane-air premixed flames containing more than 5% ammonia were measured for the first time under high pressure. In this article we present an extensive set of measured data obtained using a constant volume combustion chamber. These data and speciation data measured by other researchers were used to optimize the reduced reaction model in this study.
    The paper reveals the effect of pressure on the response of the laminar burning velocity to flame stretch rate. The Lewis number is insensitive to changes in pressure, however it was clarified that an increase in pressure enhances thermos-diffusive effects through the influence of an increase in the Zel'dovich number. On the other hand, it was shown that an accurate prediction of the laminar burning velocity and NO concentrations in ammonia flames through numerical simulations strongly depends on the prediction accuracy of O, H, and OH radical concentrations. The reduced reaction model has been optimized to accurately predict the laminar burning velocity and concentrations of OH, NO, and NH for ammonia-air and ammonia-methane-air flames over a wide range of conditions.

  • ASPACC 2021 Young Investigator Award

    2021年12月   Asia-Pacific section of the Combustion Institute  

    　詳細を見る

    受賞区分：国際学会・会議・シンポジウム等の賞 

  • 2021年　日本燃焼学会　奨励賞

    2021年11月   日本燃焼学会  

  • 2020年度　日本燃焼学会　論文賞

    2020年12月   日本燃焼学会  

    　詳細を見る

    Low-NOx NH3-air combustion power generation technology was developed by using a 50-kWe class micro gas-turbine system at the National Institute of Advanced Industrial Science and Technology (AIST), Japan, for the first time. Based on the global demand for carbon-free power generation as well as recent advances involving gas-turbine technologies, such as heat-regenerative cycles, rapid fuel mixing using strong swirling flows, and two-stage combustion with equivalence ratio control, we developed a low-NOx NH3-air non-premixed combustor for the gas-turbine system. Considering a previously performed numerical analysis, which proved that the NO reduction level depends on the equivalence ratio of the primary combustion zone in a NH3-air swirl burner, an experimental study using a combustor test rig was carried out. Results showed that eliminating air flow through primary dilution holes moves the point of the lowest NO emissions to the lesser fuel flow rate. Based on findings derived by using a test rig, a rich-lean low NOx combustor was newly manufactured for actual gas-turbine operations. As a result, the NH3 single fueled low-NOx combustion gas-turbine power generation using the rich-lean combustion concept succeeded over a wide range of power and rotational speeds, i.e., below 10–40 kWe and 75,000–80,000 rpm, respectively. The NO emissions were reduced to 337 ppm (16% O2), which was about one-third of that of the base system. Simultaneously, unburnt NH3 was reduced significantly, especially at the low electrical power output, which was indicative of the wider operating range with high combustion efficiency. In addition, N2O emissions, which have a large Global Warming Potential (GWP) of 298, were reduced significantly, thus demonstrating the potential of NH3 gas-turbine power generation with low environmental impacts.

  • 2019年度　日本燃焼学会　論文賞

    2019年11月   日本燃焼学会  

    　詳細を見る

    This paper focuses on the potential use of ammonia as a carbon-free fuel, and covers recent advances in the development of ammonia combustion technology and its underlying chemistry. Fulfilling the COP21 Paris Agreement requires the de-carbonization of energy generation, through utilization of carbon-neutral and overall carbon-free fuels produced from renewable sources. Hydrogen is one of such fuels, which is a potential energy carrier for reducing greenhouse-gas emissions. However, its shipment for long distances and storage for long times present challenges. Ammonia on the other hand, comprises 17.8% of hydrogen by mass and can be produced from renewable hydrogen and nitrogen separated from air. Furthermore, thermal properties of ammonia are similar to those of propane in terms of boiling temperature and condensation pressure, making it attractive as a hydrogen and energy carrier. Ammonia has been produced and utilized for the past 100 years as a fertilizer, chemical raw material, and refrigerant. Ammonia can be used as a fuel but there are several challenges in ammonia combustion, such as low flammability, high NOx emission, and low radiation intensity. Overcoming these challenges requires further research into ammonia flame dynamics and chemistry. This paper discusses recent successful applications of ammonia fuel, in gas turbines, co-fired with pulverize coal, and in industrial furnaces. These applications have been implemented under the Japanese ‘Cross-ministerial Strategic Innovation Promotion Program (SIP): Energy Carriers’. In addition, fundamental aspects of ammonia combustion are discussed including characteristics of laminar premixed flames, counterflow twin-flames, and turbulent premixed flames stabilized by a nozzle burner at high pressure. Furthermore, this paper discusses details of the chemistry of ammonia combustion related to NOx production, processes for reducing NOx, and validation of several ammonia oxidation kinetics models. Finally, LES results for a gas-turbine-like swirl-burner are presented, for the purpose of developing low-NOx single-fuelled ammonia gas turbine combustors.

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論文

  • Chemical kinetics of Lean − Rich − Lean fuel-air staged NH3/H2-air combustion for emission control 査読 国際共著

    Y. Vijrumbana, M. Srinivasarao, E.C. Okafor, B.R. Giri, V. M. Reddy

    Fuel   383   133813   2025年3月

    　詳細を見る

    記述言語：英語   掲載種別：研究論文（学術雑誌）  

    DOI： https://doi.org/10.1016/j.fuel.2024.133813

    DOI： https://doi.org/10.1016/j.fuel.2024.133813

    その他リンク： https://doi.org/10.1016/j.fuel.2024.133813

  • Flame stabilization and emission characteristics of ammonia combustion in lab-scale gas turbine combustors: Recent progress and prospects 査読 国際共著 国際誌

    Meng Zhang, Xutao Wei, Zhenhua An, Ekenechukwu C. Okafor, Thibault F. Guiberti, Jinhua Wang, Zuohua Huang

    Progress in Energy and Combustion Science   106   101193   2025年1月

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    記述言語：英語   掲載種別：研究論文（学術雑誌）  

    DOI： https://doi.org/10.1016/j.pecs.2024.101193

    その他リンク： https://doi.org/10.1016/j.pecs.2024.101193

  • Achieving High Flame Stability with Low NO And Zero N2O And NH3 Emissions During Liquid Ammonia Spray Combustion with Gas Turbine Combustors 査読 国際誌

    Okafor E.C., Kurata O., Yamashita H., Iki N., Inoue T., Jo H., Shimura M., Tsujimura T., Hayakawa A., Kobayashi H.

    Proceedings of the Combustion Institute   40   105340   2024年11月

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    担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

    Liquid ammonia spray direct injection is more desirable than gaseous ammonia injection in large scale gas turbine combustors because it enables a larger volumetric energy density and allows a reduction in cost and size of the fuel supply system. However, previous studies have shown that the large evaporative cooling effects of liquid ammonia droplets vaporization impair flame stabilization, and inhibit efficient control of emissions such as NO, N2O and unburned fuels. This article reports the development and testing of a novel two-stage gas turbine combustor for pure liquid ammonia spray, which achieves approximately zero N2O and unburned fuel emissions with NO emissions as low as 282 ppmv (@16% O2) in a 50 kW micro gas turbine combustor test rig. The combustor design focused on optimization of the secondary injection holes to prevent the dilution of the primary zone (PZ) by air injected into the secondary zone; improving mixture formation using a multi-nozzle twin-fluid atomizer; and elongation of the combustor length to allow sufficient fluid residence time for N2O reduction as well as droplets vaporization and combustion. It was found that the mitigation of PZ dilution resulted in a significant increase in the combustion temperature thereby encouraging efficient combustion of the liquid droplets. On the other hand, the multi-nozzle twin fluid atomizer resulted in a more uniform combustor wall temperature, a more efficient combustion and lower NOx emissions than a single-nozzle pressure swirl atomizer. It is considered that the multi-nozzle injector allowed for an improved droplets dispersion, which is necessary to mitigate large local heat extraction from the flame. These features of the combustor enabled a substantial improvement in liquid ammonia spray flame stability and a better simultaneous control of NO, N2O and unburned fuel emissions never reported before

    DOI： https://doi.org/10.1016/j.proci.2024.105340

    その他リンク： https://doi.org/10.1016/j.proci.2024.105340

  • Enhancement of liquid ammonia combustion by a twin-fluid atomizer 査読

    Kurata O., Okafor E.C., Yamashita H., Inoue T., Tsujimura T., Iki N., Hayakawa A., Kobayashi H.

    International Journal of Gas Turbine, Propulsion and Power Systems   15 ( 4 )   2024年7月

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    記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ASME International  

    The effects of atomizer type on flame stabilization and emissions from a liquid ammonia gas-turbine combustor were studied to explore the impact of enhanced fuel-air mixing. A twin-fluid atomizer is expected to enhance the mixing of atomized fuel and air, which may decrease the amount of unburnt fuel at the combustor outlet owing to improved combustion efficiency. Liquid ammonia was used as fuel, and the combustor pressure was 0.25 MPa abs. A low combustor pressure tends to encourage the partial vaporization of liquid ammonia in the mixing chamber of the twin-fluid atomizer. When the pressure of the mixing chamber was below the design value, a lower pressure, which may encourage flash boiling and hence rapid atomization, enabled a decrease in the emission of unburnt NH3 compared with that of the pressure-swirl atomizer. However, higher levels of unburned ammonia emissions were observed when the mixing chamber pressure reached the design value, suggesting that flash boiling, which promotes atomization, may enhance combustion efficiency.

    DOI： https://doi.org/10.38036/jgpp.15.4_v15n4tp02

  • Combustion and Emission Characteristics of an Ammonia Microgas Turbine Combustor With a Twin-Fluid Atomizer 査読 国際誌

    Jo H., Shimura M., Kurata O., Okafor E.C., Yamashita H., Inoue T., Tsujimura T., Iki N., Fan Y.

    Journal of Engineering for Gas Turbines and Power   146 ( 11 )   2024年6月   （ ISSN:0742-4795 eISSN:1528-8919 ）

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    記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Engineering for Gas Turbines and Power  

    In this study, combustion and emission characteristics in the test rig of microgas turbine with liquid ammonia fuel injection using the twin-fluid atomizers (TFAs) are investigated and compared with the previous result using the pressure-swirl atomizer (PSA). The combustion situation was simulated using the test rig of microgas turbine, and experiments were conducted by controlling the ratio of ammonia and methane to create a pure ammonia combustion situation. The TFA has spray cone angles of 60 deg, 90 deg, and 120 deg, and its combustion characteristics were analyzed and compared with the PSA. At 60 deg TFA, the blow-off of ammonia flame occurred before the pure ammonia combustion stage, and the flame blow-off occurred after the pure ammonia combustion at the 90 deg and 120 deg TFAs. This means that the blow-off of ammonia flame easily occurred when the spray cone angle of the atomizer is small, because the recirculation flow to the upstream of ammonia flame is weak. In addition, the 90 deg and 120 deg TFAs showed significantly reduced emissions of NO, N2O, and unburned NH3 compared to the 60 deg TFA and PSA. This can be concluded that a large spray cone angle forms a strong recirculation flow within the combustor, and emissions are reduced because the high-temperature zone sufficiently stays in the primary combustion zone.

    DOI： 10.1115/1.4065715

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書籍等出版物

  • Techno-Economic Challenges of Green Ammonia as an Energy Vector; Chapter 7: Applications

    De Vries N.; Okafor E. C.; Woo Y.; Giles A.; Valera-Medina A.（ 担当： 共著）

    2021年10月 

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    記述言語：英語   著書種別：学術書

    DOI： 10.1016/B978-0-12-820560-0.00007-2

  • Techno-Economic Challenges of Green Ammonia as Energy Vector; Chapter 6:Use of Ammonia for Heat, Power and Propulsion

    De Vries N.; Okafor E. C.; Guesta-Bozo M.; Xiao H.; Valera-Medina A.（ 担当： 共著）

    Academic Press  2021年10月 

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    記述言語：英語   著書種別：学術書

    DOI： 10.1016/B978-0-12-820560-0.00006-0

講演・口頭発表等

  • Combustion characteristics of hydrogen/oxygen/argon mixtures

    2023年12月 

    　詳細を見る

    開催年月日： 2023年12月

    記述言語：英語  

    国名：日本国  

  • Effects of light olefins, ethanol and ETBE on the laminar burning velocity and the Markstein lengths of premixed flames of multicomponent fuels consisting of gasoline components

    2023年12月 

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    開催年月日： 2023年12月

    記述言語：英語  

    国名：日本国  

  • The Development of Ammonia Combustion Technology for Gas Turbine Power Generation 招待 国際会議

    Ekenechukwu C. Okafor

    30th Korea Gas Saftey Seminar  2023年11月 

    　詳細を見る

    開催年月日： 2023年11月

    記述言語：英語   会議種別：口頭発表（一般）  

    国名：大韓民国  

  • Laminar burning velocity of hydrogen/oxygen/argon premixed laminar flames

    2023年11月 

    　詳細を見る

    開催年月日： 2023年11月

    記述言語：英語  

    国名：日本国  

  • Development of Liquid Ammonia Spray Combustion Technology for Gas Turbines 招待

    Ekenechukwu C. Okafor

    2023年9月 

    　詳細を見る

    開催年月日： 2023年9月

    記述言語：英語   会議種別：口頭発表（招待・特別）  

    国名：日本国  

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MISC

  • カーボンフリーアンモニア燃料の製造及び利用技術 : 福島再生可能エネルギー研究所における取り組み (特集 水素・脱炭素燃料の最新動向(その1))

    壹岐 典彦, 難波 哲哉, 倉田 修, Okafor Ekenechukwu, 辻村 拓

    日本ガスタービン学会誌   2021年3月

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    記述言語：日本語  

所属学協会

  • Combustion Institute

  • 日本ガスタービン学会

  • 日本燃焼学会

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  • 日本機会学会

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共同研究・競争的資金等の研究課題

  • Data-Driven Surrogate Modelling for Liquid Ammonia Direct Injection Spray Characteristics 国際共著

    2024年3月 - 2027年3月

    Royal Society, London  

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    担当区分：研究分担者 

  • Investigation of a novel lean-lean two-stage combustion strategy for the control of NOx from swirl combustors fueled with mixtures of ammonia and hydrogen.

    研究課題/領域番号：23K13263  2023年4月 - 2025年3月

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Early-Career Scientists

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    担当区分：研究代表者  資金種別：科研費

  • アンモニア・天然ガス用工業炉のバーナに関する研究開発

    2022年4月 - 2024年6月

    共同研究

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    担当区分：研究分担者  資金種別：その他産学連携による資金

FD参加状況

  • 2023年1月   役割：参加   名称：【シス情FD】若手教員による研究紹介⑦

    主催組織：部局

他大学・他機関等の客員・兼任・非常勤講師等

  • 2023年  Jiangsu University, China  区分:客員教員  国内外の区分:国外 

    学期、曜日時限または期間：2023年1月から2023年12月

  • 2022年  産業技術総合研究所  区分:客員教員  国内外の区分:国内 

    学期、曜日時限または期間：2022年1月から2026年1月まで