令和５年度原子力規制庁委託成果報告書

東京電力福島第一原子力発電所事故時の水素爆発における可燃性有機ガスの影響に関する調査

長岡技術科学大学
令和６年３月

目

次

１．事業名

1

２．事業目的1

３．事業内容1

３．１ 概要1

３．２ 実施内容

2４．試験成果4

４．１ 火炎色等確認試験

4４．１．１ 試験装置

4４．１．２ 試験条件とプロセス

5４．１．３ 試験結果と考察

5

４．２ 水素等燃焼試験

14４．２．１ 試験装置

14４．２．２ 試験条件とプロセス

15

４．２．３ 試験結果と考察

16① 水素燃焼試験16

② 混合気体燃焼試験
５．最新の知見2339

５．１ 最新知見の論文リスト

39

５．２ 論文の概要

43

６．まとめ

62

７．参考文献63

１．事業名
令和５年度原子力施設等防災対策等委託費（東京電力福島第一原子力発電所事故時の水素爆発における可燃性有機ガスの影響に関する調査）事業

２．事業目的東京電力福島第一原子力発電所（以下「１F」という。）事故等を踏まえた重大事故時の対策や
安全評価手法並びに安全対策の高度化に関連する技術的知見を取得する。本事業では、１F１号機及び３号機の原子炉建屋において発生した爆発現象に関して、水素濃度等及び可燃性有機ガスの影響を把握することを目的に、水素及び可燃性有機ガス濃度、初期ガス温度をパラメータ
として、火炎色等確認試験 （拡散燃焼試験）及び予混合燃焼試験を計画し実施する。

３．事業内容３．１ 概要本事業では、水素及び可燃性有機ガスの燃焼による水素燃焼時の挙動を把握するため、水素及び可燃性有機ガスの濃度、初期ガス温度等をパラメータとして、下記に示す燃焼試験等を実施する。
（１）火炎色等確認試験（拡散燃焼試験）の計画及び実施（２）水素等燃焼試験（予混合燃焼試験）の計画及び実施（３）水素及び混合気体燃焼に関する最新知見の収集（４）報告書の作成
試験の条件設定に関しては、原子力規制庁が実施した令和４年度原子力施設等防災対策等
委託費（東京電力福島第一原子力発電所事故時の水素爆発における可燃性有機ガスの影響に関する調査）事業の結果を参考とする。

1

３．２ 実施内容
３．２．１ 火炎色等確認試験（拡散燃焼）の計画及び実施
水素ガス及び可燃性有機ガスの火炎色等確認試験の計画及び試験を行う。燃焼試験では、水
素ガス及び可燃性有機ガス流量を調整し、拡散燃焼を一定時間維持する。なお、試験の計画及び実施では、東京電力福島第一原子力発電所事故の調査・分析に係る中間取りまとめ[1,2]を参考とする。
試験条件及び測定項目を以下に示す。
・試験条件
試験装置：ガス流量を調整し、拡散燃焼を一定時間維持
燃焼状態：拡散燃焼
水素濃度：0 vol% ～ 100 vol%可燃性有機ガス（メタン）濃度：0 vol% ～ 100 vol%不活性ガス（窒素）濃度：0 vol% ～ 50 vol%・測定項目
水素ガス及び可燃性有機ガスの流量及び温度、記録用カメラによる燃焼挙動（火炎色及び煙・煤等）、赤外線放射温度計等による火炎の温度分布
３．２．２ 水素等燃焼試験（予混合燃焼）の計画及び実施
水素ガス、可燃性有機ガス及び空気の混合気体による燃焼試験の計画及び試験を行う。水素等燃焼試験としては、次の 2 種類の燃焼試験（①水素燃焼試験、②混合気体（水素、可燃性有機ガス及び空気）燃焼試験）とする。燃焼時の挙動を把握するため、口径 30cm 以上の観察窓を有し、燃焼時の系内全体の挙動を観察・記録できる試験装置を用いて試験を行う。なお、試験の計画及び実施では、東京電力福島第一原子力発電所事故の調査・分析に係る中間取りまとめ[1,2]を参考とする。
① 水素燃焼試験
デフラグレーション（deflagration、爆燃）を考慮した燃焼時の挙動を把握する試験を実施する。
試験パラメータは水素濃度及び初期温度とし、6 ケース実施する。ここでは、1 ケースあたり 3 回の試験を行う。
試験条件及び測定項目を以下に示す。
・試験条件
試験装置：密閉型で、燃焼時圧力上昇に耐え、口径 30cm の観察窓を有する
燃焼状態：予混合燃焼
着火位置：中央部
水素濃度：10 vol%、15 vol%、20 vol%初期温度：25 ℃、75 ℃
2・測定項目
水素ガスの濃度及び温度、燃焼時の系内の圧力変化、
高速度カメラによる燃焼挙動等②混合気体（水素、可燃性有機ガス及び空気）燃焼試験①の水素燃焼試験の結果を踏まえ、水素燃焼時の可燃性有機ガス（メタン）の影響を把握する
ため、水素濃度、可燃性有機ガス濃度及び空気の混合気体による燃焼時の圧力変化並びに高速度カメラによる燃焼挙動等を測定する。試験パラメータは、ガス濃度（水素及び可燃性有機ガス）
及び初期温度とし、12 ケース実施する。ここで、混合気体の当量比は 1 以下とする。
試験条件及び測定項目を以下に示す。
・試験条件（試験装置、燃焼状態、着火位置は①と同様）
水素濃度：10 vol%、15 vol%、20 vol%可燃性有機ガス（メタン）濃度：0 vol%、1 vol%、2 vol%初期温度：25 ℃、75 ℃
・測定項目
水素ガス及び可燃性有機ガスの濃度及び温度、燃焼時の系内の圧力変化、
高速度カメラによる燃焼挙動等
３．２．３ 水素及び混合気体燃焼に関する最新知見の収集
原子力発電所事故時の水素及び混合ガスの燃焼挙動に関する研究の最新動向を調査し、今後の事故分析に資するようにまとめる。調査範囲は文献及び海外研究機関の実験施設等とし、必要に応じて海外研究者と意見交換を実施する。
３．２．４ 報告書の作成
上記３．２．１～３について報告書にまとめる。報告書には、成果のみならず各試験における前提条件及びプロセスも記載する。

3

４．試験成果
４．１ 火炎色等確認試験
４．１．１ 試験装置
本試験では、水素/メタン混合気、水素/メタン/窒素混合気を取り扱い、内径 11 ㎜のブンゼン
バーナーを用いて、拡散噴流火炎を形成させる。水素濃度、メタン濃度、窒素濃度、ガス総流量を変化させて試験を実施し、燃焼挙動を観察すると共に火炎の温度分布等を測定する。
図１はブンゼンバーナーを示したものであり、管の内径は 11 ㎜、外径は 13 ㎜、長さは 97 ㎜である。

図１ ブンゼンバーナー

図２ 燃焼試験システム
4

図２は燃焼試験システムを示したものである。火炎の画像は、デジタルカメラ（Nikon D5600）を用いて、シャッター速度 1/15 s、F 値 7.1、ISO 感度 4000 及び有効画素数 2416 万画素で撮影した。火炎の温度分布は、赤外線サーモグラフィカメラ（アビオニクス InfReC R300BP-OF）を用いて測定した。このとき、放射率は R タイプ熱電対（線径 100 µm）による火炎温度から設定した。ガスが水素のみの場合は、微量（1-2%）のメタンを添加した。
４．１．２ 試験条件とプロセス
ブンゼンバーナーに流入させる混合気は、初期温度 25℃（298 K）、初期圧力 1 気圧（101.3 kPa）、所定の水素濃度（0～100 vol%）、所定のメタン濃度（0～100 vol%）、所定の窒素濃度（0～50 vol%）とした。ガス総流量は、1.0 L/min、2.0 L/min とした。このとき、平均流速は、それぞれ、0.18 m/s、0.35 m/s である。ブンゼンバーナーに流入させる水素、メタン、窒素の流量は、デジタルマスフロ
ーコントローラー（アズビル F4Q）で制御した。
ブンゼンバーナーに流入させる混合気における水素濃度、メタン濃度、窒素濃度は、表１の通りである。
表１ 水素濃度、メタン濃度、窒素濃度
100-0-0, 90-10-0, 70-30-0, 50-50-0,
H2-CH4-N2[%]

30-70-0, 10-90-0, 0-100-0
75-0-25，67.5-7.5-25，52.5-22.5-25，37.5-37.5-25，
22.5-52.5-25，7.5-67.5-25，0-75-25
50-0-50，45-5-50，35-15-50，25-25-50，
15-35-50，5-45-50，0-50-50

４．１．３ 試験結果と考察
水素/メタン混合気を取り扱い、ガス総流量が 1.0 L/min のときの拡散火炎の直接写真を示したのが図３である。水素濃度が高いときは、火炎を確認することが困難である。メタン濃度が高くなると、薄オレンジ色の輝炎が観察される。これは遊離した炭素から発せられるものである。また、バーナー出口近傍では、青色の炎が観察される。これは CH 発光によるものである[3]。
図４は、ガス総流量が 2.0 L/min のときの直接写真である。全体として、火炎は長くなる。水素濃度が高いとき、薄い赤い炎が観察される。これは水蒸気の発光によるものである。なお、この薄い赤い炎は、暗室における試験において確認されるものであり、屋外では水素火炎を目視で確認することは困難である。
図５と図６は、ガス総流量が 1.0 L/min と 2.0 L/min のときの温度分布を示したものである。水素濃度が高いときの方が、温度は高くなる。また、ガス総流量が大きくなると、若干ではあるが温度は高くなる。
5水素/メタン/窒素混合気を取り扱い、窒素濃度が 25 %、ガス総流量が 1.0 L/min と 2.0 L/min のときの拡散火炎の直接写真を示したのが図７と図８である。混合気に窒素が加わる、つまり燃料である水素とメタンの濃度が低下することにより、火炎は短くなり、火炎の色は薄くなる。図９と図１０は、ガス総流量が 1.0 L/min と 2.0 L/min のときの温度分布を示したものである。混合気に窒素が加わることにより、温度は低下する。
窒素濃度をさらに高くし、50 % とする。図１１と図１２は、ガス総流量が 1.0 L/min と 2.0 L/minのときの直接写真を示したものであり、図１３と図１４は温度分布を示したものである。窒素濃度がさらに高くなると、火炎はさらに短くなり、火炎の色はさらに薄くなる。
火炎の最高温度を示したのが図１５である。ガス総流量が大きくなると、最高温度は若干上昇する。また、窒素濃度が高くなると、最高温度は低下する。これは、供給される燃料（水素とメタン）の量が少なくなるからである。さらに、水素濃度が高い方が、最高温度は高くなる。これは、水素
火炎温度の方がメタン火炎温度より高いからである。
拡散燃焼の試験では、全ての条件において、煙の発生は確認されなかった。一方、煤について
は、メタンが燃料に含まれる場合、薄オレンジ色の輝炎が観察されていることから、その発生が確認された。また、拡散火炎の上にスチール板を置いて試験を行い、その表面に煤が付着していることを確認した。

6図３ 火炎の直接写真（ガス総流量 1.0 L/min、水素濃度 0～100 vol%、メタン濃度 0～100 vol%、窒素濃度 0 vol%）図４ 火炎の直接写真（ガス総流量 2.0 L/min、水素濃度 0～100 vol%、メタン濃度 0～100 vol%、窒素濃度 0 vol%）7

図５ 火炎の温度分布（ガス総流量 1.0 L/min、水素濃度 0～100 vol%、メタン濃度 0～100 vol%、窒素濃度 0 vol%）図６ 火炎の温度分布（ガス総流量 2.0 L/min、水素濃度 0～100 vol%、メタン濃度 0～100 vol%、窒素濃度 0 vol%）8

図７ 火炎の直接写真（ガス総流量 1.0 L/min、水素濃度 0～75 vol%、メタン濃度 0～75 vol%、窒素濃度 25 vol%）図８ 火炎の直接写真（ガス総流量 2.0 L/min、水素濃度 0～75 vol%、メタン濃度 0～75 vol%、窒素濃度 25 vol%）9

図９ 火炎の温度分布（ガス総流量 1.0 L/min、水素濃度 0～75 vol%、メタン濃度 0～75 vol%、窒素濃度 25 vol%）図１０ 火炎の温度分布（ガス総流量 2.0 L/min、水素濃度 0～75 vol%、メタン濃度 0～75 vol%、窒素濃度 25 vol%）10

図１１ 火炎の直接写真（ガス総流量 1.0 L/min、水素濃度 0～50 vol%、メタン濃度 0～50 vol%、窒素濃度 50 vol%）図１２ 火炎の直接写真（ガス総流量 2.0 L/min、水素濃度 0～50 vol%、メタン濃度 0～50 vol%、窒素濃度 50 vol%）11

図１３ 火炎の温度分布（ガス総流量 1.0 L/min、水素濃度 0～50 vol%、メタン濃度 0～50 vol%、窒素濃度 50 vol%）図１４ 火炎の温度分布（ガス総流量 2.0 L/min、水素濃度 0～50 vol%、メタン濃度 0～50 vol%、窒素濃度 50 vol%）12

図１５ 火炎の最高温度（ガス総流量 1.0～2.0 L/min、水素濃度 0～100 vol%、メタン濃度 0～100 vol%、窒素濃度 0～50 vol%）13

４．２ 水素等燃焼試験
４．２．１ 試験装置
本試験では、①水素/空気混合気（水素燃焼試験）、②水素/メタン/空気混合気（混合気体燃焼試験）を取り扱い、水素濃度とメタン濃度を変化させて、口径 30 cm の観察窓を有する密閉型
容器内で燃焼試験を実施する。容器内に予混合気を充填し、中心点火することにより、球状のデフラグレーション（deflagration、爆燃）を観察し、水素濃度による燃焼時の挙動及びメタン濃度による水素燃焼への影響を把握する。ここでは、シュリーレン法により、火炎伝播の様子や火炎面形状を高速度撮影する。また、容器内の圧力変化を測定する。
図１６は密閉型燃焼容器を示したものであり、表２はその基本仕様を示したものである。

表２ 密閉型燃焼容器の基本仕様

容器

観察窓

図１６ 密閉型燃焼容器

図１７ 燃焼試験システム
14

容積

73 L

材質

SUS

直径

300 mm

厚み

140 mm数4図１７は燃焼試験システムを示したものである。燃焼容器には、ガス供給ライン、排気ライン、
真空引きラインを設け、ガス供給ラインと排気ラインのすべての弁は、遠隔から電気的に操作できるように設定している。真空引きやガス供給時の容器内部圧力の測定用としてピエゾ抵抗センサ（Keller PAA-23Y）、容器内部の混合気温度の測定用にシース熱電対（T-type）を設置している。
燃焼時の容器内の急激な圧力変化を取得するため、圧電センサ（Kistler 6045A）を燃焼器上部に設けたポートに直接取り付け、圧電センサ用チャージアンプ（Kistler 5918A）より出力された電圧を
データロガー（キーエンス NR-600）によってサンプリング周波数 10 kHz で記録した。また、火炎形状および動的な伝播挙動を広範囲に取得するため、直径 350 mm の凹面鏡を有するシュリー
レン法測定装置（溝尻光学工業所 SL-350）により観察した。シュリーレン画像は、高速度ビデオ
カメラ (Photron FASTCAM SA-X) を用いて、撮影速度 10000 fps、シャッター速度 20 µs、および
解像度 1024×1024 pixels で撮影した。
４．２．２ 試験条件とプロセス
燃焼容器に充填する混合気は、初期温度 25℃（298 K）、75℃（348 K）、初期圧力 1 気圧（101.3kPa）、所定の水素濃度（10 vol%、15 vol%、20 vol%）、所定のメタン濃度（0 vol%、1 vol%、2 vol%）とした。所定の水素濃度とメタン濃度になるように、分圧に関するドルトンの法則に基づいて気体を混合した。
燃焼試験では、容器内に①水素/空気混合気、②水素/メタン/空気混合気を充填した後、電極により容器の中心で点火し、高速度ビデオカメラによるシュリーレン撮影、及び圧電センサによる圧力測定を行った。燃焼試験は、①で 6 ケース、②で 12 ケース、全体で 18 ケース実施し、燃焼時の系内の燃焼挙動と圧力変化を把握した。なお、試験条件は表３の通りである。
表３ 試験条件

初期温度

水素濃度

メタン濃度

初期温度

水素濃度

メタン濃度

［℃］

［％］

［％］

［℃］

［％］

［％］

10

0

10

0

10

1

10

1

10

2

10

2

15

0

15

0

15

1

15

1

15

2

15

2

20

0

20

0

20

1

20

1

20

2

20

2

25

75

15

４．２．３ 試験結果と考察①水素燃焼試験
球状のデフラグレーションの伝播の様子を示したのが図１８（上部）である。ここで、初期温度は25℃、初期圧力は 1 気圧、水素濃度は 10 vol%であり、メタン濃度は 0 vol%である。点火後 0.1 msのシュリーレン画像、及び火炎半径 𝑟𝑟b = 2 cm、4 cm、6 cm、8 cm、10 cm のときの画像が示されている。火炎半径の増加と共に火炎面にセルが形成され、それが発達して複雑な形状になる様子が観察されている。このセルの形成は予混合火炎の固有不安定性に起因するものである[4]。

また、球状の火炎が全体として上方へ移動することが確認される。これは浮力によるものであり、燃焼速度が小さい予混合火炎で顕著に現れる挙動である。本試験では、口径 30 cm の観察窓を有する燃焼容器を用いていることから、この条件下での浮力の影響を示すことが出来ている。燃焼現象を把握するには、十分広い観察窓を有する燃焼容器を用いる必要がある。
容器内の圧力変化を示したのが図１８（下部）である。燃焼反応が進行すると共に、容器内圧力は急激に上昇する。燃焼反応が完了した後、圧力は降下する。これは、燃焼容器から周囲への熱損失により既燃ガス温度が低くなるからである。なお、図中の火炎半径が最も大きいとき、容器内圧力は初期圧力より 1 割程度高くなっている[5]。つまり、火炎を可視化した図（上部の図）は、圧力が上昇しきる前の時間帯のものである。
初期温度が 25℃、水素濃度が 15 vol% と 20 vol% のときのシュリーレン画像を示したのが、図１９と図２０の上部である。水素濃度が高くなると共に、火炎の伝播速度は増大している。これは予混合火炎の燃焼速度が大きくなるからである[6]。また、容器内の最大圧力は上昇する（図１９と図２０の下部参照）。これは断熱火炎温度が高くなるからである[7]。なお、水素濃度 20 vol% における燃焼後の圧力変化が大きいのは、火炎温度が高いため周囲への熱損失が大きくなるからである。
初期温度が 75℃、水素濃度が 10 vol%、15 vol%、20 vol% のときのシュリーレン画像を示したのが、図２１から図２３の上部である。初期温度が高くなると、火炎の伝播速度は増大する。これは反応速度が増大し、燃焼速度が大きくなるからである。また、火炎面の凹凸は滑らかになっている。
これは固有不安定性のレベルが低下するからである。さらに、容器内の最大圧力は、水素濃度が低いとき上昇し、水素濃度が高いとき下降する（図２１から図２３の下部参照）。これは、燃焼時における周囲への熱損失によるものである[8]。

16図１８ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 25℃、初期圧力 1 気圧、水素濃度 10 vol%、メタン濃度 0 vol%）17

図１９ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 25℃、初期圧力 1 気圧、水素濃度 15 vol%、メタン濃度 0 vol%）18

図２０ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 25℃、初期圧力 1 気圧、水素濃度 20 vol%、メタン濃度 0 vol%）19

図２１ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 75℃、初期圧力 1 気圧、水素濃度 10 vol%、メタン濃度 0 vol%）20

図２２ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 75℃、初期圧力 1 気圧、水素濃度 15 vol%、メタン濃度 0 vol%）21

図２３ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 75℃、初期圧力 1 気圧、水素濃度 20 vol%、メタン濃度 0 vol%）22

②混合気体燃焼試験
初期温度が 25℃、水素濃度 10 vol%、メタン濃度 1 vol%、2 vol% におけるデフラグレーションのシュリーレン画像と容器内圧力変化を示したのが図２４（メタン濃度 1 vol%）と図２５（メタン濃度 2vol%）である。ここで、混合気体の当量比は、メタン濃度 0 vol%、1 vol%、2 vol% において、それぞれ、0.265、0.375、0.487 である。メタン濃度が高くなると共に、火炎の伝播速度は増大し、容器内の最大圧力は上昇する。前者は予混合火炎の燃焼速度が大きくなることによるもので、後者は断熱火炎温度が高くなることによるものである。
水素濃度が 15 vol% のときの試験結果を示したのが図２６（メタン濃度 1 vol%）と図２７（メタン濃度 2 vol%）である。ここで、混合気体の当量比は、メタン濃度 0 vol%、1 vol%、2 vol% において、それ
ぞれ、0.420、0.539、0.660 である。また、水素濃度が 20 vol% の試験結果を示したのが図２８（メタン濃度 1 vol%）と図２９（メタン濃度 2 vol%）である。ここで、混合気体の当量比は、それぞれ、0.595、0.723、0.855 である。メタン濃度が高くなると共に、火炎の伝播速度は増大する。これは混合気の当量比が高くなり、予混合火炎の燃焼速度が大きくなるからである。
初期温度が 75℃、水素濃度が 10 vol%、15 vol%、20 vol% のときのシュリーレン画像を示したのが、図３０から図３５の上部である。初期温度が高くなると、火炎の伝播速度は増大する。また、容器内の最大圧力は、水素濃度が低いとき上昇し、水素濃度が高いとき下降する（図３０から図３５の下部参照）。これらの傾向は、初期温度が 25℃の場合と同様である。
図３６は、初期温度が 25℃のときの容器内の最大圧力を示したものである。水素濃度及びメタン濃度が高くなると共に、単調に上昇する。最大圧力の上昇は、水素爆発による破壊力を強めることに直結するものである。初期温度が 75℃のときの容器内の最大圧力を示したのが図３７である。また、表４は、初期温度が 25℃、75℃のときの容器内の最大圧力を示している。本試験では、
1 ケースあたり 3 回の試験を行っており、表４に示した最大圧力は平均値である。それゆえ、図１８から図３５に示した最大圧力と若干の違いが生じている。初期温度が高くなると、容器内の最大圧
力は、水素濃度が低いとき上昇し、水素濃度が高いとき下降する。これは、燃焼時間が長いと熱損失が増大することによるものである[8]。

23図２４ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 25℃、初期圧力 1 気圧、水素濃度 10 vol%、メタン濃度 1 vol%）24

図２５ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 25℃、初期圧力 1 気圧、水素濃度 10 vol%、メタン濃度 2 vol%）25

図２６ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 25℃、初期圧力 1 気圧、水素濃度 15 vol%、メタン濃度 1 vol%）26

図２７ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 25℃、初期圧力 1 気圧、水素濃度 15 vol%、メタン濃度 2 vol%）27

図２８ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 25℃、初期圧力 1 気圧、水素濃度 20 vol%、メタン濃度 1 vol%）28

図２９ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 25℃、初期圧力 1 気圧、水素濃度 20 vol%、メタン濃度 2 vol%）29

図３０ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 75℃、初期圧力 1 気圧、水素濃度 10 vol%、メタン濃度 1 vol%）30

図３１ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 75℃、初期圧力 1 気圧、水素濃度 10 vol%、メタン濃度 2 vol%）31

図３２ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 75℃、初期圧力 1 気圧、水素濃度 15 vol%、メタン濃度 1 vol%）32

図３３ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 75℃、初期圧力 1 気圧、水素濃度 15 vol%、メタン濃度 2 vol%）33

図３４ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 75℃、初期圧力 1 気圧、水素濃度 20 vol%、メタン濃度 1 vol%）34

図３５ デフラグレーションのシュリーレン画像と容器内圧力変化（初期温度 75℃、初期圧力 1 気圧、水素濃度 20 vol%、メタン濃度 2 vol%）35

図３６ 容器内の最大圧力（初期温度 25℃、初期圧力 1 気圧、水素濃度 10～20 vol%、メタン濃度 0～2 vol%）36

図３７ 容器内の最大圧力（初期温度 75℃、初期圧力 1 気圧、水素濃度 10～20 vol%、メタン濃度 0～2 vol%）表４ 容器内の最大圧力（初期温度 25℃、75℃）

37東京電力福島第一原子力発電所の水素爆発における 3 号機 3 階天井部の梁の損傷に関して、大梁とその周囲の床板に 300～500kPa（ゲージ圧）程度の圧力が 20～40ms 程度の間作用すると、大梁に観察された変形と同程度の変形が生じうるとの報告がある[1]。本試験で得られた結果（図３８、図３９）と中間取りまとめに記載されている解析結果には、整合性が有るものと考えられる。

図３８ 容器内の最大圧力（初期温度 75℃）

図３９ 容器内の圧力変化（初期温度 75℃、初期圧力 1 気圧、水素濃度 15 vol%、メタン濃度 1 vol%）38

５．最新の知見
水素及び混合気体燃焼に関する最新知見を収集し、拡散燃焼及び予混合燃焼に関する知見を整理した。それらは、以下の通りである。
５．１ 最新知見の論文リスト
水素/可燃性有機ガス拡散燃焼（噴流）
1.
Karbasi, M., Wierzba, I., The effects of hydrogen addition on the stability limits of methane jet
diffusion flames, International Journal of Hydrogen Energy, Vol. 23 (1998), pp. 123-129, DOI:
10.1016/S0360-3199(97)00031-1.
2.
Burbano, H. J., Amell, A. A., Garcia, J. M., Effects of hydrogen addition to methane on the flame
structure and CO emissions in atmospheric burners, International Journal of Hydrogen Energy,Vol. 33 (2008), pp. 3410-3415, DOI: 10.1016/j.ijhydene.2008.04.020.
3.
Wu, L., Kobayashi, N., Li, Z., Huang, H., Li, J., Emission and heat transfer characteristics ofmethane-hydrogen hybrid fuel laminar diffusion flame, International Journal of Hydrogen Energy,Vol. 40 (2015), pp. 9579-9589, DOI: 10.1016/j.ijhydene.2015.05.096.
4.
Wu, L., Kobayashi, N., Li, Z., Huang, H., Experimental study on the effects of hydrogen addition on
the emission and transfer characteristics of laminar methane diffusion flames with oxygenenriched air, International Journal of Hydrogen Energy, Vol. 41 (2016), pp. 2023-2036, DOI:
10.1016/j.ijhydene.2015.10.132.
5.
Patel, V., Shah, R., Effect of hydrogen enrichment on combustion characteristics of methane
swirling and non-swirling inverse diffusion flame, International Journal of Hydrogen Energy, Vol.
44 (2019), pp. 28316-28329, DOI: 10.1016/j.ijhydene.2019.09.076.
6.
Oztuna, S., Buyukakin, M. K., Effects of hydrogen enrichment of methane on diffusion flame
structure and emissions in a back-pressure combustion chamber, International Journal of
Hydrogen Energy, Vol. 45 (2020), pp. 5971-5986, DOI: 10.1016/j.ijhydene.2019.09.187.

39

（対向流）
7.
Liu, Y., Zhang, J., Ju, D., Shi, L., Han, D., Second-law thermodynamics analysis on non-premixed
counterflow methane flames with hydrogen addition, Journal of Thermal Analysis andCalorimetry, Vol. 139 (2020), pp. 2577-2583, DOI: 10.1007/s10973-019-08583-0.
8.
Khare, R., Vlavakis, P., Langenthal, T. V., Loukou, A., Khosravi, M., Kramer, U., Trimis, D.,Experimental investigation of the effect of hydrogen addition on the sooting limit and structureof methane/air laminar counterflow diffusion flames, Fuel, Vol. 324, 124506 (2022), DOI:
10.1016/j.fuel.2022.124506.
9.
Eckart, S., Rong, F. Z., Hasse, C., Krause, H., Scholtissek, A., Combined experimental andnumerical study on the extinction limits of non-premixed H2/CH4 counterflow flames withvarying oxidizer composition, International Journal of Hydrogen Energy, Vol. 48 (2023), pp.
14068-14078, DOI: 10.1016/j.ijhydene.2022.12.061.
10.
Prieler, R., Moser, M., Eckart, S., Krause, H., Hochenauer, C., Machine learning techniques topredict the flame state, temperature and species concentrations in counter-flow diffusion flames
operated with CH4/CO/H2-air mixtures, Fuel, Vol. 326, 124915 (2022), DOI:
10.1016/j.fuel.2022.124915.
（層流）
11.
Kim, J. S., Park, J., Kwon, O. B., Yun, J. H., Keel, S. I., Kim, T. K., Preferential diffusion effects on
NO formation in Methane/Hydrogen-air diffusion flames, Energy & Fuels, Vol. 22 (2008), pp. 278283, DOI: 10.1021/ef700505a.
12.
Gao, J., Hossain, A., Nakamura, Y., Flame base structures of micro-jet hydrogen/methane
diffusion flames, Proceedings of the Combustion Institute, Vol. 36 (2017), pp. 4209-4216, DOI:
10.1016/j.proci.2016.08.034.
13.
Antar, E., Delavande, J., Robert, E., Experimental characterization of diffusive-thermal
instabilities in CO2-diluted H2-CH4-CO unstrained diffusion flames, Combustion and Flame, Vol.
250, 112636 (2023), DOI: 10.1016/j.combustflame.2023.112636.
14.
Seok, B. H., Kim, J. S., Yoon, S. H., Hwang. J., Park, D. G., Study on behavior and emission of
methane/hydrogen diffusion flame with applied DC electric field, Journal of Advanced Marine40

Engineering and Technology, Vol. 47 (2023), pp. 211-218,
DOI: 10.5916/jamet.2023.47.5.211.
（乱流）
15.
Gnentedem, C., Awakem, D., Obounou, M., Fouda, H. P. E., Njomo, D., Application of a reduced
mechanism by computational singular perturbation method to the calculation of the ignition
delays of turbulence diffusion flame CH4/H2/N2, Journal of Energy Resources Technology, Vol.
142, 062302 (2020), DOI: 10.1115/1.4045478.
16.
Hafid, M., Hebbir, N., Lacroix, M., Joly, P., CFD modellimg of a turbulent CH4/H2/N2 jet diffusion
flame with detailed chemistry, Heat and Mass Transfer, Vol. 59 (2023), pp. 583-598, DOI:
10.1007/s00231-022-03283-2.
水素/可燃性有機ガス/空気予混合燃焼（燃焼速度）
17.
Bradley, D., Lawes, M., Mumby, R., Burning velocity and Markstein length blending laws formethane/air and hydrogen/air blends, Fuel, Vol. 187 (2017), pp. 268–275, DOI:
10.1016/j.fuel.2016.09.032.
18.
Shang, R., Zhuang, Z., Yang, Y., Li, G., Laminar flame speed of H2/CH4/air mixtures with CO2 andN2 dilution, International Journal of Hydrogen Energy, Vol. 47 (2022), pp. 32315–32329, DOI:
10.1016/j.ijhydene.2022.07.099.
19.
Hasche, A., Navid, A., Krause, H., Eckart, S., Experimental and numerical assessment of theeffects of hydrogen admixtures on premixed methane-oxygen flames, Fuel, Vol. 352, 128964(2023), DOI: 10.1016/j.fuel.2023.128964.
20.
Al-Khafaji, M., Yang, J., Tomlin, A. S., Thompson, H. M., Boer, G., Liu, K., Morsy, M. E., Laminarburning velocities and Markstein numbers for pure hydrogen and methane/hydrogen/air mixturesat elevated pressures, Fuel, Vol. 354, 129331 (2023), DOI: 10.1016/j.fuel.2023.129331.
（乱流）
21.
Park, J., Minamoto, Y., Shimura, M., Tanahashi, M., Effects of hydrogen enrichment on CH4/Air
turbulent swirling premixed flames in a cuboid combustor, International Journal of Hydrogen
41

Energy, Vol. 45 (2020), pp. 9039–9051, DOI: 10.1016/j.ijhydene.2019.12.175.
22.
Hazim Shehab, Hiroaki Watanabe, Yuki Minamoto, Ryoichi Kurose, Toshiaki Kitagawa,Morphology and structure of spherically propagating premixed turbulent hydrogen - air flames,
Combustion and Flame, Vol. 238, 111888 (2021), DOI: 10.1016/j.combustflame. 2021.111888
（超音速）
23.
Chaumeix, N., Pichona, S., Lafossea, F., Paillarda, C. E., Role of chemical kinetics on thedetonation properties of hydrogen /natural gas/air mixtures, International Journal of Hydrogen
Energy, Vol. 32 (2007), pp. 2216–2226, DOI: 10.1016/j.ijhydene.2007.04.008.
24.
Ciccarelli, G., Chaumeix, N., Mendiburu, A. Z., N’Guessan, K., Comandini, A., Fast-flame limit forhydrogen/methane-air mixtures, Proceedings of the Combustion Institute, Vol. 37 (2019), pp.
3661–3668, DOI: 10.1016/j.proci.2018.06.045.
（動的挙動）
25.
Kiymaz, T. B., Boncu, E., Guleryuz, D., Karaca, M., Yilmaz, B., Allouis, C., Gokalp, I., Numericalinvestigations on flashback dynamics of premixed methane-hydrogen-air laminar flames,
International Journal of Hydrogen Energy, Vol. 47 (2022), pp. 25022–25033, DOI:
10.1016/j.ijhydene.2022.05.230.
26.
Bayramoglu, K, Bahlekeh, A., Masera, K., Numerical investigation of the hydrogen, ammonia andmethane fuel blends on the combustion emissions and performance, International Journal of
Hydrogen Energy, Vol. 48 (2023), pp. 39586–39598, DOI: 10.1016/j.ijhydene.2023.06.079.
27.
Giannotta, A., Cherubini, S., Palma, P. D., The effect of hydrogen enrichment on thermoacoustic
instabilities in laminar conical premixed methane/air flames, International Journal of Hydrogen
Energy, Vol. 48 (2023), pp. 37654–37665, DOI: 10.1016/j.ijhydene.2023.06.118.
（球状火炎）
28.
Okafor, E. C., Hayakawa, A., Nagano, Y., Kitagawa, T., Effects of hydrogen concentration onpremixed laminar flames of hydrogen-methane-air, International Journal of Hydrogen Energy, Vol.
39, Issue 5 (2014), pp. 2409–2417, DOI: 10.1016/j.ijhydene.2013.11.128.
29.
Wang, X. R., Zhang, Y., Li, T., Ma, Y., Zhang, J., Xu, C., Investigation of cellularization
42

characteristics of hydrogen-methane-ethanol expanding spherical flame at elevated pressures,
Combustion and Flame, Vol. 255, 112866 (2023), DOI: 10.1016/j.combustflame.2023.112866.
30.
Ma, Q., Zhang, Q., Chen, J., Huang, Y., Shi, Y., Effects of hydrogen on combustion characteristics
of methane in air, International Journal of Hydrogen Energy, Vol. 39 (2014), pp. 11291–11298,
DOI: 10.1016/j.ijhydene.2014.05.030.
31.
Lei, B., Wei, Q., Pang, R., Xiao, J., Kuznetsov，M., Jordan, T., The effect of hydrogen addition on
methane/air explosion characteristics in a 20-L spherical device, Fuel, Vol. 338, 127351 (2023),
DOI: 10.1016/j.fuel.2023.127351.
（長岡技術科学大学）
32.
Katsumi, T., Aida, T., Aiba, K., Kadowaki, S., Outward propagation velocity and acceleration
characteristics in hydrogen-air deflagration, International Journal of Hydrogen Energy, Vol. 42(2017), pp. 7360–7365, DOI: 10.1016/j.ijhydene.2016.06.165.
33.
Katsumi, T., Kumada, M., Noguchi, H., Zenba, A., Sato, D., Yamagata, H., Kadowaki, S., Effects ofinert-gas addition on the dynamic behavior and propagation characteristics of spherically
expanding hydrogen-air flames, Journal of Thermal Science and Technology, Vol. 18, No. 2, 2300310 (2023), DOI: 10.1299/jtst.23-00310.
34.
Kadowaki, S., Katsumi, T., Sato, D., Noguchi, H., Zemba, A., Iwanaga, K., Abe, S., Characteristics ofspherically expanding hydrogen-methane-air lean premixed flames in a closed chamber: aiming toelucidate the hydrogen explosion at Fukushima Daiichi Nuclear Power Station, MechanicalEngineering Letters, Vol. 10, 23-00586, (2024), DOI: 10.1299/mel.23-00586.
５．２ 論文の概要
水素/可燃性有機ガス拡散燃焼（噴流）
1.
The effects of hydrogen addition on the stability limits of methane jet diffusion flames
The flame stability limits of confined jet diffusion flames (JDFs) flowing into a co-axial oxidizing
stream was studied both experimentally and analytically. Methane and hydrogen and their mixtures
were used as the fuel. The experiments were conducted with two different jet diameters and within
a wide range of co-flowing stream velocities and hydrogen concentrations in methane or air stream.
43

The hydrogen diffusion flame was found to have a much larger region of stable operation than themethane JDF. Higher stability of the methane JDFs was achieved by the addition of hydrogen toeither the jet fuel or the surrounding air stream. A hysteresis phenomena were observed in thereattachment process of lifted flames. It was found that the conditions prior to ignition of theflame, such as the value of co-flowing stream and jet velocities and position of the ignitor, havesignificant effect on the type of flame stabilization mechanism and flame blowout limits. The
optimum ignition conditions for achieving higher blowout limits were investigated. The blowout
limits of lifted JDFs were significantly affected by the velocity of co-flowing stream. The present
study also reports the results of the calculation of the blowout limits of lifted JDFs using as acriterion the ratio of mixing time scale to characteristic combustion time scale. The agreement of
the experimental and calculated data was satisfactory.
2.
Effects of hydrogen addition to methane on the flame structure and CO emissions inatmospheric burners
Hydrogen addition to methane will have an important role to reach a fully developed hydrogen
economy. The effects of this addition on the flame structure and CO emissions were evaluated in
two different atmospheric burners. Four fuels with the following composition were used: 100%CH4,
2%H2+98%CH4, 6%H2+94%CH4 and 15%H2+85%CH4. In a single-port atmospheric burner, adecreasing trend in the height of the blue cone with hydrogen addition was determined. The
increase in the laminar burning velocity was identified as the main effect on the behavior of thisparameter. In a drilled-port atmospheric burner, a significant reduction in CO emissions withhydrogen addition was achieved under two operating conditions: (1) keeping the primary air ratio
constant and (2) keeping the primary air ratio and the thermal input constant. The results obtained
were consistent with previous experimental studies. This reduction is attributed to a higher
concentration of OH radicals as a result of hydrogen addition.
3.
Emission and heat transfer characteristics of methane-hydrogen hybrid fuel laminar diffusion
flame
The effect of adding hydrogen to methane on the emission and heat transfer characteristics
of a laminar diffusion flame was investigated. The total input thermal energy for each test was
kept constant. The results showed that adding hydrogen increased the temperature, decreased
the flame length, and significantly increased the soot-free length fraction. CO and CO2 emission
decreased with the addition of hydrogen. The more efficient oxidation of CO to CO2 at higherhydrogen fractions was the main contributor to the reduction of CO, whereas decreased carbon
input was the dominant factor for the reduction of CO2. The NOx emission increased owing to theincrease of prompt, thermal NOx formation and NNH pathway. The ratio of radiative heat flux tototal heat flux decreased, and the radiative heat flux did not exceed 5% of the total heat flux. The
addition of hydrogen improved the total heat flux by approximately 20%.
44

4.
Experimental study on the effects of hydrogen addition on the emission and transfer
characteristics of laminar methane diffusion flames with oxygen-enriched air
The effects of hydrogen addition on the emission and heat transfer characteristics of oxygenenriched laminar methane diffusion flames were investigated in a laboratory-scale furnace with aco-axial burner. The volume fraction of hydrogen in the methane-hydrogen blend was varied from
0% to 50%, and the oxygen concentration was varied from 25% to 35%. Results showed that theaddition of hydrogen led to an increase in the soot-free length and flame temperature while thedegree of increase was less at higher oxygen concentrations. Adding hydrogen chemicallyenhanced the oxidation of CO to CO2, and this chemical effect was stronger when the oxygen
concentration increased. NOx emissions increased significantly with the addition of hydrogen, while
the rate of this increase decreased with greater oxygen concentrations. The total heat flux
increased with the addition of hydrogen, while the rate of this increase was less at higher oxygen
concentrations. Although the radiative heat flux increased with higher oxygen concentrations, it
did not exceed 6% of the total heat flux at 35% O2. Moreover, adding hydrogen decreased theradiative heat flux; this decrease was significant at higher oxygen concentrations.
5.
Effect of hydrogen enrichment on combustion characteristics of methane swirling and nonswirling inverse diffusion flame
Influence of hydrogen addition on appearance of swirling and non-swirling inverse diffusion
flame (IDF) along with emissions characteristics are investigated experimentally. The combustion
characteristics including flame length, axial and radial temperature variation, and noise level are
analyzed for hydrogen addition in methane by mass basis for constant energy input and by volume
basis for constant volumetric fuel flow rate. Hydrogen addition in methane IDF produces shorter
flame by compressing entrainment zone, mixing zone, reaction zone, and post-combustion zone.
Hydrogen addition shift these zones towards fuel and air exit from the burner. Enrichment ofmethane with hydrogen on a mass basis up to 6% reduces CO emission considerably and increases
NOx emission moderately. Effect of H2 addition on combustion and emission characteristics ismore prominent in nonswirling IDF. Combustion noise is augmented with the hydrogen addition andthe magnitude of sound level depends on the hydrogen concentration.
6.
Effects of hydrogen enrichment of methane on diffusion flame structure and emissions in a
back-pressure combustion chamber
In the present study, the effects of hydrogen enrichment of methane are investigatednumerically from the diffusion flame structure and emissions aspect. Fluent code is utilized as thesimulation tool. In the first part of the study, four experiments were conducted using natural gas
as fuel. A non-premixed burner and a back-pressure boiler were utilized as the experimental setup.
45

The natural gas fuel consumption rate was changed between 22 Nm3/h and 51 Nm3/h. After theexperimental studies, the numerical simulations were performed. The non-premixed combustion
model with the steady laminar flamelet model (SFM) approach was used for the calculations. The
methane-air extinction mechanism was utilized for the calculation of the chemical species. The
numerical results were verified with the experimental results in terms of the flue gas emissions
and flue gas temperature values. In the second part of the study, four different hydrogen-enrichedmethane combustion cases were simulated using the same methane-air extinction mechanism,
which included the hydrogen oxidation mechanism as a sub mechanism. The same energy input(432 kW) was supplied into the boiler for all the studied cases. The obtained results show that thehydrogen addition to methane significantly change the diffusion flame structure in the combustion
chamber. The hydrogen-enriched flames become broader and shorter with respect to the puremethane flame. This provides better mixing of the reactants and combustion products in the flame
regions due to the use of a back-pressure boiler. In this way, the maximum flame temperature
values and thermal NO emissions are reduced in the combustion chamber, when the hydrogen
addition ratio is less than 15% by mass. The maximum temperature value is calculated as 2030 K
for the case with 15% hydrogen addition ratio by mass, while it is 2050 K for the case withouthydrogen enrichment. Therefore, it is determined that the hydrogen-enriched methane combustion
in a back-pressure combustion chamber has the potential of reducing both the carbon and thermal
NO emissions.
（対向流）
7.
Second-law thermodynamics analysis on non-premixed counterflow methane flames withhydrogen addition
Natural gas is an attractive alternative fuel because of its environment-friendly nature, andhydrogen addition is considered as an efficient method to improve the methane combustion
performance in combustion engines. In this study, the exergy destruction characteristics in nonpremixed counterflow methane flames are numerically studied based on the second law ofthermodynamics. The irreversible processes during combustion, such as heat conduction, massdiffusion and chemical reactions, are studied, and it is found that heat conduction is the dominantfactor in exergy destruction. Additionally, the exergy destruction from each source shows two
peaks, and their overall impact causes the total exergy destruction to exhibit three peaks.
Moreover, the effects of hydrogen addition on exergy destruction from each source are evaluated.
The effect of hydrogen addition on the exergy destruction from heat conduction is insignificant,and the exergy destruction from mass diffusion increases with hydrogen addition. For the exergy
destruction from chemical reactions, the carbon-containing reactions are key to the first peak of
the exergy destruction rate, whereas the H2-O2 system reactions are more important for thesecond peak. The contribution of chemical reactions to the overall exergy destruction decreases
46with H2 addition.
8.
Experimental investigation of the effect of hydrogen addition on the sooting limit and structureof methane/air laminar counterflow diffusion flames
The influence of hydrogen (H2) addition on the sooting limit and structure of methane/air
laminar counterflow diffusion flames has been studied. Soot limits have been obtained using thelaser light scattering technique for CH4∕H2 mixtures with H2 concentration varying from 0–20%
by volume in the fuel mixture for different strain rates. The resulting soot limit map shows asignificant increase in the fuel concentration at the soot limit with increasing amounts of H2. To
understand this trend, temperature and species concentration profiles have been measured andcompared under the influence of H2 addition in (a) an incipiently sooting and (b) in a sooting
CH4/air flame. Flame temperatures have been measured using a thin-wire S-type thermocouple
and species profiles have been measured using the gas chromatography technique (GC). The
results indicate a significant decrease in the amounts of higher hydrocarbons such as benzene
and naphthalene (which are considered important soot precursors) with an increase in H2
concentration for the sooting flame. To explain this decrease in the concentration of higherhydrocarbons, pathway analysis has been performed to elucidate the influence of H2 on theformation and consumption of soot forming species.
9.
Combined experimental and numerical study on the extinction limits of non-premixed H2/CH4
counterflow flames with varying oxidizer composition
Chemical reaction mechanisms with detailed kinetics are an important topic in combustion
science and an essential prerequisite for the accurate modeling of reactive flows in combustors.
Besides isolating and studying individual reactions, the development of reaction mechanisms isoften based on well-defined experimental observables, such as the laminar burning velocity andthe ignition delay time. While many optimization targets are associated with premixed combustion,
the extinction strain rate (ESR) of non-premixed flames in the counterflow configuration is anotherwell-defined experimental observable which, however, often receives less attention. In order toreduce the scarcity of corresponding datasets for the emerging fuel hydrogen and its blends withmethane, this work reports ESR measurements for H2, CH4/H2 and CH4 counterflow diffusion
flames considering a variation of the oxygen content in the oxidizer stream between 14 % and 21 %.
The experimental investigation is complemented by calculations with a 1D counterflow modelutilizing a temperature-control continuation method in order to determine the extinction limits
numerically. The simulations are performed with six different well-established chemical reaction
mechanisms. It is shown from both, experimental and numerical results, that with the substitutionof CH4 by H2 the ESR increases and further, that the ESR decreases with a reduction of theoxygen content in the oxidizer stream. In addition, decreasing flame temperatures are observed at
extinction as the H2 content increases. Overall, all mechanisms are able to qualitatively recover47

the trends found for varying H2 contents, fuel mole fraction, and oxygen content in the oxidizer.
However, significant quantitative deviations are observed between the numerical results regarding
the ESR values and the deviations are larger than for other important flame characteristics, suchas the laminar burning velocity. The results suggest that the ESR could be a useful optimization
target for further improving chemical reaction mechanisms which underlines the importance ofdatasets such as the one presented in this work.
10.
Machine learning techniques to predict the flame state, temperature and species concentrations
in counter-flow diffusion flames operated with CH4/CO/H2-air mixtures
The usage of artificial intelligence (AI) is increasing in many fields of research, since complex
physical problems can be ‘learned’ and reproduced by AI methods. Thus, instead of numericallysolving partial differential equations, describing the physical processes in detail, appropriate AI
methods can be used to decrease the calculation time significantly. In the present study, artificial
neural networks (ANNs) were used to predict temperature and species concentrations in a laminar
counter-flow diffusion flame. To improve the accuracy of the ANNs, a support vector machine(SVM) was used to subdivide the wide range of operating conditions (air–fuel ratio, strain rate, fuelmixture) into ‘flame’ and ‘no flame’ cases. Due to classification with the SVM the prediction
performance of the ANNs was optimized and an average error to the reference values (GRI3.0)
below 10 K for all cases was detected, whereas the calculation time was decreased by a factor of
about 4,800 (solving the transport equations with GRI3.0).
（層流）
11.
Preferential diffusion effects on NO formation in Methane/Hydrogen-air diffusion flames
A numerical study in methane/hydrogen diffusion flames has been conducted to clarify thepreferential diffusion effects of H2 and H with detailed chemistry. The composition of fuel issystematically changed from pure methane to pure hydrogen through the molar addition of H2 tomethane. A comparison was made by employing three species diffusion models, i.e., mixtureaveraged species diffusion and the suppression of the diffusivities of H and H2. The behavior of
maximum flame temperatures with the three species diffusion models is not explained by the scalardissipation rate but the nature of chemical kinetics such as the behaviors of chain carrier radicalsof H, O, and OH. It is found that the preferential diffusion of H radical into the reaction zone curbs
the populations of the chain carrier radicals and then flame temperature while that of H2 into thereaction zone produces the reduction of the scalar dissipation rate and the population of chain
carrier radicals and these force the flame temperature to decrease. These preferential diffusion
effects of H2 and H are also compared among NO emission behaviors through the three species
diffusion models. Under all flame conditions, Fenimore NO is much more remarkable compared tothermal NO. It is also seen that the preferential diffusion of H radical into the reaction zone
48

suppresses the thermal and Fenimore NO while that of H2 into the reaction zone increases them.
To facilitate the details of those NO behaviors through preferential diffusion effects of H2 and H,
importantly contributing reaction steps to the production and destruction of Fenimore NO are
addressed.
12.
Flame base structures of micro-jet hydrogen/methane diffusion flames
In this study, a comparison of flame base structures of hydrogen/methane–air diffusion flames
formed over a tiny-jet is made numerically for both isothermal and thermal conductive burnerconditions, in order to clarify the fuel dependent flame stabilization mechanisms. It is found that,
unlike a methane flame, the flame base of a hydrogen flame always attaches to the burner. The
analyses indicate that the dominant intermediate-consumption steps have significantly lower
activation energies for the hydrogen flame as compared to a methane flame. More importantly,
one of the HO2 production reactions (R43f: H + O2 + M → HO2 + M), which has a dominant rolein sustaining reactivity at the flame base, shows a negative temperature dependence, causing theheat release rate in the flame base kernel to increase as the burner wall temperature decreases.
With a thermal conductive burner (thermal conductivity of 16 W/m-K) over a wide range of fueljet velocities (0.5–4.0 m/s), it is found that the burner tip is heated to a significantly higher
temperature by a hydrogen flame due to its unique stabilization mechanism. The mixing effects ofhydrogen and methane are then considered. It is found that the burner tip temperature can be
reduced by adding methane into the fuel flow. This is because, according to the investigation of
the structures of the hydrogen/methane jet diffusion flames, the reaction rate of R43f is
suppressed due to the included intermediates (e.g., CH3, CH2O) consumption steps of methane.
It is expected that the flame attachment feature associated with the flame base structure can beeasily controlled by mixing hydrogen and methane, making it possible to control the burner tip
temperature in advance.
13.
Experimental characterization of diffusive-thermal instabilities in CO2-diluted H2-CH4-CO
unstrained diffusion flames
The combustion of multi-fuel mixtures is experimentally studied for the first time in unstrained
diffusion flames, where the parasitic hydrodynamic effects present in common research burners
are negligible. A broad range of H2–CO–CH4 fuels highly diluted in CO2 is investigated to provide
an understanding of the intrinsic diffusive-thermal instabilities (DTIs) that onset in low calorificbiomass-derived syngas. For each fuel blend, the burning intensity or the Damköhler number (Da)is gradually reduced, going through the marginal stability state where DTIs first appear, down to
the lean extinction limit. Flame stability limits are provided. From the large difference between the
Lewis numbers of the multiple fuel species (Lei), the cells that onset due to H2 are seen to interact
and compete with the pulsations from CO and CH4, leading to superimposed cellular-pulsating
instabilities. These are thoroughly characterized by measuring the pulsations amplitude, frequency,49

cell size, number of cells, and fraction of the flame sheet actively burning. An effective fuel Lewis
number (Le F,eff) calculated from the fuel mixture composition is introduced and used along with
the Damköhler number to map the DTIs observed. At lower Le F,eff and D a , the cellular attributesof the superimposed instabilities dominate, while at larger Lewis numbers and the near marginal
stability state, pulsations prevail.
14.
Study on behavior and emission of methane/hydrogen diffusion flame with applied DC electric
fieldThis experimental study investigates the effect of DC electric fields on flame behavior andemissions in non-premixed hydrogen/methane flames using a co-flow burner. The study considers
varying hydrogen mole fractions of 0.1, 0.3, and 0.5, and different fuel flow velocities of 2.0, 6.3,
and 8.0 cm/s. To introduce DC electric fields, a high voltage terminal was connected to the fuelnozzle, while the ground terminal was connected to an upper mesh located above the flame. The
applied DC voltages ranged from Vdc = -10 kV to +10 kV. The study reveals that the addition ofhydrogen reduces flame height. Furthermore, when subjected to DC electric fields, the flames
exhibit movement towards the lower potential side, displaying stable and oscillating behaviors dueto the Lorentz force acting on positive ions within the flames. The concentrations of CO and CO2
exhibit insignificant changes with varying hydrogen mole fractions. However, when exposed topositive voltage, CO, CO2, and NOX emissions are reduced. This research provides a detailed
analysis of flame/flow behavior and emission characteristics when hydrogen and DC electric fields
are introduced, providing valuable insights into the control of flame behavior and pollutant
emissions.
（乱流）
15.
Application of a reduced mechanism by computational singular perturbation method to thecalculation of the ignition delays of turbulence diffusion flame CH4/H2/N2This work presents an application of a reduced chemical kinetic mechanism using
computational singular perturbation (CSP) based on the significant indices of the modes on theevolution of species and the degree of participation of reactions. With this approach, themechanism of Yang and Pope is reduced to 22 reversible reactions (RR22). In this study, thetabulation of ignition delays is made with Yang and Pope mechanism, GRI 3.0, and the reduced
mechanism RR22; the results obtained show a good agreement among the three mechanisms. The“Modèle Intermittent Lagrangien” (MIL) necessary to calculate the chemical source term of thetransport equation of the species requires the library of ignition delays determined above and aprobability density function (PDF) of the mixture fraction presumed by a beta distribution. The
scalar variance, one of the key parameters for the determination of the presumed beta function,
is obtained by solving its own transport equation with the unclosed scalar dissipation rate modeled50

using either an algebraic model or a transport equation. All these models are introduced in thecomputational fluid dynamics “Code-Saturne” to simulate a turbulent CH4/H2/N2 jet flame (DLR
Flame A) performed at the Deutsches Zentrum für Luft-und Raumfahrt (DLR), or German
Aerospace Center. A set of comparisons is made and the results of simulations show a good
agreement among the three mechanisms as well with the experimental data.
16.
CFD modellimg of a turbulent CH4/H2/N2 jet diffusion flame with detailed chemistry
A CFD model based on the Reynolds Averaged Navier–Stokes (RANS) approach combined witha detailed chemical kinetic mechanism to investigate a turbulent CH4/H2/N2 jet diffusion flame isdeveloped. The CFD governing equations of momentum, mass, and energy in the turbulent field
were solved in conjunction with the standard k−ε turbulence model. The laminar flamelet conceptthat views the turbulent diffusion flame as an ensemble of laminar diffusion flamelets is adopted.
The coupling between turbulence and chemistry is achieved by the statistical description of threeparameters namely (1) mixture fraction (Z), (2) variance of mixture fraction (Z”2) and (3) scalardissipation rate (χ). The flamelet model consists of two steps namely (a) the generation of a setof laminar flamelet solutions and (b) the integration of the laminar flamelet solutions with
presumed-shape Probability Density Function (PDF). The GRI Mech-3.0 mechanism that involves
53 species and 325 reactions is adopted. The effect of various parameters such as C1ε constantin the turbulent dissipation transport equation on the numerical solution is highlighted. Also, thecomparison between the CFD model results and the experimental data of velocity, temperatureand mass fractions of species (CH4, H2, N2, H2O, CO2, O2 and CO) along the centreline as wellas on the radial position of x/D = 5, 40 are presented. Generally, the CFD results show a good
agreement with the experimental data, and the presented approach in this paper is an accurate
promising alternative to LES and DNS approaches for the modelling of non-premixed turbulent
configurations.
水素/可燃性有機ガス/空気予混合燃焼（燃焼速度）
17.
Burning velocity and Markstein length blending laws for methane/air and hydrogen/air blends
Because of the contrasting chemical kinetics of methane and hydrogen combustion, thedevelopment of blending laws for laminar burning velocity, ul, and Markstein length for constituent
mixtures of CH4/air and H2/air presents a formidable challenge. Guidance is sought through astudy of analytical expressions for laminar burning velocity. For the prediction of burning velocitiesof blends, six blending laws were scrutinized. The predictions were compared with the measured
burning velocities made by Hu et al. under atmospheric conditions [1]. These covered equivalence
ratios ranging from 0.6 to 1.3, and the full fuel range for H2 addition to CH4. This enabled51

assessments to be made of the predictive accuracy of the six laws. The most successful law is
one developed in the course of the present study, involving the mass fraction weighting of the
product of ul, density, heat of reaction and specific heat, divided by the thermal conductivity ofthe mixture. There was less success from attempts to obtain a comparably successful blending
law for the flame speed Markstein length, Lb, despite scrutiny of several possibilities. Details are
given of two possible approaches, one based on the fractional mole concentration of the deficient
reactant. A satisfactory empirical law employs mass fraction weighting of the product ulLb.
18.
Laminar flame speed of H2/CH4/air mixtures with CO2 and N2 dilution
The laminar flame speeds of H2/CH4/air mixtures with CO2 and N2 dilution were systematicinvestigated experimentally and numerically over a wide range of H2 blending ratios (75 vol%) with
CO2 (67 vol%) and N2 (67 vol%) dilution in the fuels. The experimental measurements wereconducted via the Bunsen flame method incorporating the Schlieren technique under the conditionof equivalence ratios from 0.8 to 2.0. To gain an insightful understanding of the experimental
observations, detailed numerical simulation was carried out using Chemkin-Pro with GRI3.0-Mech.
The experimental measurements were also used to validate the corresponding performance of asemiempirical correlation derived through asymptotic analysis method coupled with the reduced
chemistry mechanism. The results showed that at lower H2 fraction (xH2 < 0.5), the laminar flame
speeds of H2/CH4/air mixtures displayed great linearly increase with the growth of H2 fractions.
The combustion of mixtures with low H2 contents was dominated by CH4 conversion which was
mainly controlled by the increasing OH radicals produced from the key oxidation reactions of H +O2 = O + OH. With the further increase of H2 fractions, the methane-dominated combustion
gradually transformed into the methane-inhibited hydrogen combustion, resulting to the growth oflaminar flame speeds was dramatical and non-linear. Due to the larger heat capacity and chemical
kinetic effect, CO2 presented a stronger dilution effect on reducing the laminar flame speeds thanN2. With the addition of CO2, the increasing stronger competition for H radical through CO + OH
= CO2 + H with H + O2 = O + OH due to the significant reduction of H mole fractions, leading to
the larger decrease of laminar flame speeds of mixtures. Besides, although the contribution ofthermal effect of CO2 decreased near the equivalence ratio, the thermal effect of CO2 still
preformed the dominated contribution to the total dilution effect. A comparison between theexperimental data and estimated results using the semiempirical correlation showed that, thecorrelation using new modified coefficients provided the satisfactorily accuracy predictions on thelaminar flame speeds of diluted H2/CH4/air mixtures at lower xH2 (xH2 < 0.5) and lower xdilution(xdilution = 0.25). The estimated results were generally located within a deviation range of ±20%errors except for two unsatisfactory eases occurred at conditions of xH2 = 0.75 and xCO2 = 0.67.
The considerably poor predictions were attributed to the significantly variation of the chemical
kinetics under high H2 content and large CO2 dilution conditions.
19.
52

Experimental and numerical assessment of the effects of hydrogen admixtures on premixed
methane-oxygen flames
Thermal utilization of hydrogen is becoming increasingly important as the climate change
progresses. Fossil fuels such as natural gas are replaced by green hydrogen in the natural gas gridto reduce CO2 emissions. However, the switch to hydrogen causes significant changes in
combustion properties, such as higher flame temperatures or higher burning velocities. As a result,
this change in flame properties impacts application processes. In order to prevent a reduction inquality, the processes must be optimally adapted to the fuel switch. Therefore, the combustion
properties of the gas mixture have to be investigated in more detail. In this work a premixed oxyfuel combustion of hydrogen-methane mixtures under atmospheric conditions has been
investigated. Therefore, two scenarios are of further interest, low hydrogen admixture (0 vol-%, 10
vol-%, 20 vol-%, and 35 vol-%) and high hydrogen admixture (50 vol-%, 75 vol-%, 95 vol-%/100
vol-%). In this study, a premixed burner is utilized at three different burner powers with a maximum
power of 1.2 kW. The flame characteristics has been analyzed by optical (chemilumicence and OHPLIF), spectroscopic, and thermal measurements. This study aims to determine the change inflame shape, the temperature profiles at different flame heights, and the species formed in the
combustion zone. For this purpose, various compositions of hydrogen-methane-oxygen mixturesat different equivalence ratios ϕ = 0.8–1.2 are experimentally investigated at atmosphericconditions. The effect of hydrogen addition to the methane-oxygen flame has been numericallyconsidered utilizing three different mechanisms (GRI 3.0, Glarborg, and Aramco). The adiabatic
flame temperature, laminar burning velocity and radical formation have been studied numericallyfor different gas compositions.
20.
Laminar burning velocities and Markstein numbers for pure hydrogen and methane/hydrogen/air
mixtures at elevated pressures
Spherically expanding flame propagations have been employed to measure flame speeds for
H2/CH4/air mixtures over a wide range of H2 fractions (30 %, 50 %, 70 and 100 % hydrogen by
volume), at initial temperatures of 303 K and 360 K, and pressures of 0.1, 0.5 and 1.0 MPa. The
equivalence ratio (ϕ) was varied from 0.5 to 2.5 for pure hydrogen and from 0.8 to 1.2 formethane/hydrogen mixtures. Experimental laminar burning velocities and Markstein numbers formethane/hydrogen/air mixtures at high pressures, which are crucial for gas turbine applications,are very rare in the literature. Moreover, simulations using three recent chemical kinetic
mechanisms (Konnov-2018 detailed reaction, Aramco-2.0-2016 and San Diego Methane detailed
mechanism (version 20161214)) were compared against the experimentally derived laminar burning
velocities. The maximum laminar burning velocity for 30 % and 50 % H2 occurs at ϕ = 1.1. However,it shifts to ϕ = 1.2 for 70 % H2 and to ϕ = 1.7 for a pure H2 flame. The laminar burning velocities
increased with hydrogen fraction and temperature, and decreased with pressure. Unexpectedbehaviour was recorded for pure H2 flames at low temperature and ϕ = 1.5, 1.7 wherein ul did not53

decrease when the pressure increased from 0.1 to 0.5 MPa. Although, the measurement
uncertainty is large at these conditions, the flame structure analysis showed a minimum decline in
the mass fractions of the active species (H, O, and OH) with the rise in the initial pressure.
Markstein length (Lb) and Markstein number (Mab and Masr) varied non-monotonically withhydrogen volume fraction, pressure and temperature. There was generally good agreement
between simulations and experimentally derived laminar burning velocities, however, forexperiments of rich-pure hydrogen at high initial pressures, the level of agreement decreased but
remained within the limits of experimental uncertainty.
（乱流）
21.
Effects of hydrogen enrichment on CH4/Air turbulent swirling premixed flames in a cuboid
combustor
Effects of H2-enrichment on structures of CH4/air turbulent swirling premixed flames affectedby high intensity turbulence in a gas turbine model combustor are investigated by conducting
direct numerical simulations. Two stoichiometric mixture conditions, of which volume ratio of
CH4:H2 = 50:50 and 80:20, are simulated by considering a reduced chemistry (25 species and 111
reactions). Results showed qualitatively different flame shapes and reaction zone characteristics
between the cases. For the higher H2-ratio case, the flame is stabilized both in the inner and outer
shear layers. For the lower H2-ratio case, the flame is stabilized only in the inner shear layer andextinction occurs in the outer shear layer. Comparison of the reaction zone characteristics with
unstrained and strained laminar flames in phase space showed that H2 mass fraction for the lower
H2-ratio case and reaction rate profiles for both cases deviate from the corresponding laminarvalues. Analysis of fuel species conservation equation suggests that the turbulent transports aresubstantially influential to determine local and global flame structures. These findings would be
useful for designing practical H2-enriched gas turbine combustor in the aspect of flame structures
under high intensity turbulence.
22.
Morphology and structure of spherically propagating premixed turbulent hydrogen - air flames
Three-dimensional direct numerical simulations of spherically propagating premixed turbulent
stoichiometric hydrogen-air flames with detailed chemistry and detailed diffusion are employed toclarify the influence of turbulence-flame interactions with respect to flame structure andmorphology. Four cases are considered within the corrugated flamelets and the thin reaction zone
regimes. The most significant fuel consumption and heat release rates occur at the negativelycurved flamelets. Furthermore, the increments in burning velocity are lower than the increments
in flame surface area, which is due to the reduction in the local burning intensity at the positivelycurved flamelets. The morphology of intense reaction zones is quantified using Minkowski
functionals and their shapes include ”tubes”, ”pancakes”and more complex shapes, which are
54

compared to their counterparts in planar flames. As turbulence level increases, the number of
locally defined intense reaction zones increases, and their boundaries expand to cover more
extensive parts of the flame front. However, intense reaction zones’ geometrical dimensions do
not significantly differ for each flame as it propagates. Local turbulence properties are obtainedfor each intense reaction zone. The conditional averages of local Taylor microscale and local
Kolmogorov scale, conditioned based on the shape finders, are investigated. The conditional
averages of the local Taylor microscale scale correlate with the planarity and filamentary of intense
reaction zones. Therefore, turbulent motions at Taylor microscale size have a significant role incharacterizing turbulence-flame interactions relevant to flame morphology and relevant to the
local flame thickness and reaction layers of developing-flames. On the other hand, local
Kolmogorov scales’ turbulent motions show weaker or no such correlations. There is a dissidence
between global turbulence statistics and local ones representing the interactions at the flame front.
Local turbulence-flame interactions of Taylor microscale sizes occur at specific length scales,depending on the flame size and irrelevant of eddies with other length scales.
（超音速）
23.
Role of chemical kinetics on the detonation properties of hydrogen /natural gas/air mixtures
The first part of the present work is to validate a detailed kinetic mechanism for the oxidationof hydrogen–methane–air mixtures in detonation waves. A series of experiments on auto-ignition
delay times have been performed by shock tube technique coupled with emission spectrometryfor H2/CH4/O2 mixtures highly diluted in argon. The CH4/H2 ratio was varied from 0 to 4 and theequivalence ratio from 0.4 to 1. The temperature range was from 1250 to 2000K and the pressure
behind reflected shock waves was between 0.15 and 1.6MPa. A correlation was proposed between
temperature (K), concentration of chemical species (molm−3) and ignition delay times. The
experimental auto-ignition delay times were compared to the modelled ones using four different
mechanisms from the literature: GRI [Smith PG, Golden DM, Frenklach M, Moriarty NW, Goldenberg
M, et al. (http://www.me.berkeley.edu/gri_mech/)], Marinov et al. [Aromatic and polycyclicaromatic hydrocarbon formation in a laminar premixed n-butane flame. Combust Flame 1998;
114:192–213], Hughes et al. [(http://www.chem.leeds.ac.uk/Combustion/Combustion.html)],
Konnov [Detailed reaction mechanism for small hydrocarbons combustion. Release 0.5(http://homepages.vub.ac.be/∼akonnov/), 2000]. A large discrepancy was generally found between
the different models. Konnov’s model, which auto-ignition delay times predictions were the closest
to the measured ones, has been selected to calculate ignition delay times in the detonation waves.
The second part of the study concerned the experimental determination of the detonation
properties, namely detonation velocity and cell size. Effect of the initial composition, hydrogen tomethane ratio and the amount of oxygen in the mixture, as well as the initial pressure on thedetonation velocity and on the cell size were investigated. The ratio of methane/(methane +55hydrogen) varied between 0 and 0.6 for two different equivalence ratios (0.75 and 1) while theinitial pressure was fixed to 10 kPa. A correlation was established between the characteristic cellsize and the ignition delay time behind the leading shock of the detonation. It was clearly shownthat methane has an important inhibitor effect on the detonation of these combustible mixtures.
24.
Fast-flame limit for hydrogen/methane-air mixtures
Flame acceleration experiments were performed in a 10 cm inner-diameter tube filled withevenly spaced 0.43 blockage ratio orifice plates. The critical mixture composition required for flame
acceleration to a fast-flame was measured for four methane/hydrogen fuel-air mixtures at initial
temperatures of 298K, 423K, and 573K. These conditions provide a large range in the Zeldovich
number between 12 and 28, where the Zeldovich number was calculated from the laminar burning
velocity obtained from 1-D flame simulations. The data collapsed very well when the expansion
ratio across the flame (calculated at the critical condition) was plotted versus the Zeldovich
number. This is consistent with correlation proposed by Dorofeev [7], that was based on
experimental data obtained over a narrower Zeldovich number range. For pure hydrogen fuel, thecritical expansion ratio was found to be between 2 and 4, and for pure methane the criticalexpansion ratio was as high as 8, for an initial temperature of 573K.
（動的挙動）
25.
Numerical investigations on flashback dynamics of premixed methane-hydrogen-air laminarflamesInjecting hydrogen into the natural gas network to reduce CO2 emissions in the EU residential
sector is considered a critical element of the zero CO2 emissions target for 2050. Burning natural
gas and hydrogen mixtures has potential risks, the main one being the flame flashback phenomenon
that could occur in home appliances using premixed laminar burners. In the present study, twodimensional transient computations of laminar CH4 + air and CH4 + H2 + air flames are performed
with the open-source CFD code Open FOAM. A finite rate chemistry based solver is used tocompute reaction rates and the laminar reacting flow. Starting from a flame stabilized at the rimof a cylindrical tube burner, the inlet bulk velocity of the premixture is gradually reduced to observe
flashback. The results of the present work concern the effects of wall temperature and hydrogen
addition on the flashback propensity of laminar premixed methane-hydrogen-air flames. Completesequences of flame dynamics with gradual increases of premixture velocity are investigated. At
the flame flashback velocities, strong oscillations at the flame leading edge emerge, causing broken
flame symmetry and finally flame flashback. The numerical results reveal that flashback tendency
increase with increasing wall temperature and hydrogen addition rate.
26.
Numerical investigation of the hydrogen, ammonia and methane fuel blends on the combustion
56

emissions and performance
The co-combustion of traditional methane gas and alternative fuels importance to reduce
emissions in combustion has increased in recent years. The literature proves the successful
operations of ammonia and hydrogen as diesel engine fuels. However, there is not sufficient
information about the combustion of methane along with ammonia and hydrogen. In this study, theeffects of the combustion of methane-hydrogen and methane-ammonia-hydrogen fuel mixture on
system performance and emissions are numerically investigated. Firstly, the effects of methane
and 5%, 10%, and 15% hydrogen mixture are investigated. Then, methane and 5% fixed hydrogenratio with 5% ammonia, 10% ammonia, and 15% ammonia mixtures are examined. The numericalmodel is validated against the literature data using the Sandia D model with a difference of 5.9%
at x/d = 0.5. As a result of the study, 15% hydrogen addition to methane increased the maximum
combustion chamber temperature by 100 K. However, with the addition of 15% of ammonia, thetemperature is dropped by 200 K and the peak temperature location is slightly shifted away fromthe injection point. A 10% enhancement of hydrogen content rate will cause a 28% increase inthermal NOX emission and a 10% increment in the ammonia content of the fuel blend has caused
to 3000 ppm enhancement in NOX emission. With the addition of %5, 10%, and %15 ammonia massfraction to methane and hydrogen blend fuel at the axial location of x/d = 0.444, the NOx emission
production rate has been increased by 1970, 3010, and 3790 ppm, respectively. In addition, the
15% hydrogen addition to methane (85% methane/15% hydrogen) and 5% hydrogen plus 15% ammonia
addition to methane (80% methane/5% hydrogen/15% ammonia) reduced the CO2 emission by 30.7%
and 14% compared to neat methane (100% methane) combustion. To sum up, this study shows thatthe use of methane-ammonia-hydrogen as a diesel engine fuel reduces combustion emissions.
27.
The effect of hydrogen enrichment on thermoacoustic instabilities in laminar conical premixed
methane/air flames
We perform a conceptual study about the linear stability of a hydrogen-enriched methane-air
premixed laminar flame inside a cylindrical duct with both ends open. The flame and acoustic
subsystems are coupled using the Flame Transfer Function (FTF). The power output is set to a
constant value and the hydrogen molar fraction of the fuel mixture is varied. We show that addinghydrogen reduces the flame length and impacts the FTF in two ways: (i) gain drop-off shifts
towards higher frequencies and (ii) phase lag reduces. Then, we compute the eigenvalues of thethermoacoustic system varying the hydrogen molar fraction. We show that adding hydrogen to thefuel mixture can stabilize linearly unstable systems and vice versa, depending on the duct natural
frequencies. The results show that the hydrogen molar fraction can be a tunable parameter forcontrolling thermoacoustic instabilities.

57

（球状火炎）28.
Effects of hydrogen concentration on premixed laminar flames of hydrogen-methane-air
The unstretched laminar burning velocities and Markstein numbers of spherically propagatinghydrogen-methane-air flames were studied at a mixture pressure of 0.10 MPa and a mixture
temperature of 350 K. The fraction of hydrogen in the binary fuel was varied from 0 to 1.0 at
equivalence ratios of 0.8, 1.0 and 1.2. The unstretched laminar burning velocity increased nonlinearly with hydrogen fraction for all the equivalence ratios. The Markstein number varied nonmonotonically at equivalence ratios of 0.8 and 1.0 and increased monotonically at equivalence ratioof 1.2 with increasing hydrogen fraction. Analytical evaluation of the Markstein number suggested
that the trends could be due to the effective Lewis number, which varied non-monotonically withhydrogen fraction at equivalence ratios of 0.8 and 1.0 and increased monotonically at 1.2. The
propensity of flame instability varied non-monotonically with hydrogen fraction at equivalence
ratios of 0.8 and 1.0.
29.
Investigation of cellularization characteristics of hydrogen-methane-ethanol expanding sphericalflame at elevated pressures
The incorporation of ethanol into hydrocarbon fuels for use is attracting increasing interestand it is necessary to investigate its inherent flame instability for better application in combustion
units. The instability of hydrogen-methane-ethanol spherically expanding flame has been
investigated at an initial temperature of 400 K, initial pressures of (2–4 bar), ethanol fraction of(20%, 50%, 80%), and equivalence ratios (Ф) of (0.7–1.4) using the constant volume combustion
chamber (CVCC). High-speed schlieren technology was used to record flame propagation images.
The effects of hydrodynamic and thermal-diffusion effect on the inherent instability of the flame
were investigated. As the ethanol ratio increased, the hydrodynamic effect was enhanced. The
thermal-diffusion effect was discovered to stabilize the flame surface under all conditions, as
judged jointly by the effective Lewis number and the critical Lewis number. The critical conditions(critical radius and Peclet number) at the onset of instability were evaluated, and it was found thatthe flames were more prone to flame instability at higher pressures. The critical Peclet number
increased with the increase in the equivalence ratio when the ethanol ratio was 20%, and showed
the opposite trend when the ethanol ratio was 50% and 80%. In addition, as the ethanol ratio
increases, the stability of the lean mixtures flame increases, while the rich mixtures flame suffersfrom early on- set of instability. The theoretical and experimental results were consistent, withsome differences at Ф = 1.4. An empirical correlation formula for the critical Peclet number (Pec) and Markstein number (M b) was further proposed (Pe c = 18.03 M b + 214.78). Finally, theKarlovitz number was used to study the instability behavior of the flame. The critical Karlovitz
number (Ka c) decreased with increasing M b and the tendency of the flame to suffer frominstability diminished, and the following correlation was obtained Ka c = 0.05635 ×exp (−0.13852
58M b). Furthermore, the flame was more unstable in rich mixtures, this was consistent with theconclusion of instability derived from the critical radius.
30.
Effects of hydrogen on combustion characteristics of methane in air
The explosion process of multi-component gas mixture is extremely complex and may cause
serious disaster effects. The safety issue concerning explosion of multi-component gas mixtureis urgent to be investigated on account of its wide range of applications. In current work, series ofexperiments were performed in a 20 L spherical explosion vessel at initial conditions of 1 atm and
293 K, involving methane-hydrogen/air mixtures. The proportion of hydrogen in fuels varied from
0% to 100%. It was observed that peak temperature is always behind the peak pressure in arrival
time whatever the fuel equivalence is. Experimental values of peak overpressure are lower thanadiabatic ones due to heat loss. It was also founded that the hydrogen addition can raise explosion
pressure and temperature in experiment but slightly decrease that in adiabatic condition, and boththe increase in experiment and the decrease in adiabatic show a linear correlation versus the
proportion of hydrogen. Hence the deviation between the experimental results and the adiabatic
results decreases as the hydrogen proportion rises. Moreover, the positive effect of hydrogen
addition on (dp/dt)max is very slight at low hydrogen proportion, while the effect becomes much
more pronounced at higher hydrogen contents, showing an exponential growth. For each fuelcomposition throughout all experiments, the peak overpressure, peak temperature and (dp/dt)max
concerning fuel equivalence ratios of 0.6, 1 and 1.5 follow a same rule: Ф = 1 is the highest,
followed by Ф = 1.5 and Ф = 0.6. Finally, the MIEs of gaseous methane-hydrogen/air mixtures ata fuel equivalence ratio of 1.5 were measured as a function of hydrogen proportion. It shows asharp decrease as the fraction of hydrogen in fuel rises, from 118 mJ for methane-air to 0.12mJ
for hydrogen-air. It is also observed that the MIE of multi-component gas mixtures can beapproximately figured as the linear weighted sum of the MIE of each component; the weighting
factor is respectively the volume fraction of each component. This can be considered as auniversal method to obtain the MIE for a specific multi-component gas.
31.
The effect of hydrogen addition on methane/air explosion characteristics in a 20-L sphericaldevice
The addition of hydrogen to methane changes its deflagration characteristics and increases
the combustion rate. However, studies on the effect of hydrogen on methane deflagration remain
insufficient. Therefore, based on the CFD code GASFLOW-MPI, a four-step combustionmechanism model was established for methane/hydrogen mixtures. The deflagration
characteristics of a premixed combustible gas in a 20-L spherical device was numerically simulatedusing a methane/hydrogen/air equivalence ratio of 1 and hydrogen addition in the range of 0–50%;
subsequently.

The

results

werecomparedwithexperimental

data.

The

four-stepmethane/hydrogen combustion-mechanism could effectively reproduce the methane/hydrogen59

deflagration process on considering the heat losses. With an increase in hydrogen addition, thelaminar burning velocity increases, and the deflagration duration reduces. It decreases the
explosion heat loss and increased the maximum deflagration pressure. Under adiabatic simulation,
the maximum deflagration pressure decreased with an increase in hydrogen addition, in contrast
with

the

experimental

results.

This

indicates

that

the

heat-loss

effectofthemethane/hydrogen/air-mixture deflagration process should not be ignored. Moreover, the heatloss during the methane/hydrogen/air-mixture deflagration was mainly caused by thermal radiation.
Thus, the influence of the thermal-radiation and convective heat-transfer mechanisms should beconsidered in the numerical simulations of methane/hydrogen/air-mixture deflagration.
（長岡技術科学大学）
32.
Outward propagation velocity and acceleration characteristics in hydrogen-air deflagration
Propagation characteristics of hydrogen-air deflagration need to be understood for an accurate
risk assessment. Especially, flame propagation velocity is one of the most important factors.
Propagation velocity of outwardly propagating flame has been estimated from burning velocity ofa flat flame considering influence of thermal expansion at a flame front; however, this conventional
method is not enough to estimate an actual propagation velocity because flame propagation isaccelerated owing to cellular flame front caused by intrinsic instability in hydrogen-air deflagration.
Therefore, it is important to understand the dynamic propagation characteristics of hydrogen-air
deflagration. We performed explosion tests in a closed chamber which has 300 mm diameter
windows and observed flame propagation phenomena by using Schlieren photography. In the
explosion experiments, hydrogen-air mixtures were ignited at atmospheric pressure and room
temperature and in the range of equivalence ratio from 0.2 to 1.0. Analyzing the obtained Schlieren
images, flame radius and flame propagation velocity were measured. As the result, cellular flame
fronts formed and flame propagations of hydrogen-air mixture were accelerated at the all
equivalence ratios. In the case of equivalent ratio 0.2, a flame floated up and could not propagate
downward because the influence of buoyancy exceeded a laminar burning velocity. Based uponthese propagation characteristics, a favorable estimation method of flame propagation velocity
including influence of flame acceleration was proposed. Moreover, the influence of intrinsic
instability on propagation characteristics was elucidated.
33.
Effects of inert-gas addition on the dynamic behavior and propagation characteristics ofspherically expanding hydrogen-air flames
To investigate the effects of inert-gas addition on the dynamic behavior and propagation
characteristics of spherically expanding hydrogen-air flames, the experiments of premixed
combustion were performed in a closed chamber. The dynamic behavior of premixed flames wascaught by high-speed Schlieren imaging, and the flame radius and propagation velocity were60

measured by analyzing the Schlieren photography. When the flame radius was sufficiently small,smooth flame surface was observed, where the flame stretch affected strongly the propagation
velocity. From the correlation between the propagation velocity and flame stretch rate, weestimated the propagation velocity of unstretched flame and the Markstein length including
thermal-expansion effects. When the flame radius was large, on the other hand, cellular surface
induced by intrinsic instability was observed, and then the flame acceleration was confirmed. As
the results, the critical flame radius corresponding to the occurrence of flame acceleration andthe increment coefficient of propagation velocity were obtained. It was found that the increment
coefficient became larger at low equivalence ratios, which was because the diffusive-thermal
instability became stronger. Under the conditions of high concentration of inert gas, the increment
coefficient of propagation velocity became smaller. This was because the burning velocity became
lower by increasing the inert-gas concentration. Moreover, we obtained the increment coefficient
normalized by the propagation velocity of unstretched flame. The normalized increment coefficientincreased as the inert-gas concentration became higher, which indicated that the addition of inert
gas promoted the instability of hydrogen flames. Based on the dynamic behavior and propagation
characteristics of premixed flames, the parameters of flame acceleration model depending on theinert-gas concentration were obtained, and then the flame propagation velocity was predicted.
34.
Characteristics of spherically expanding hydrogen-methane-air lean premixed flames in a closed
chamber: aiming to elucidate the hydrogen explosion at Fukushima Daiichi Nuclear Power Station
In the hydrogen explosion at Fukushima Daiichi Nuclear Power Station, the presence offlammable organic compounds together with hydrogen in reactor buildings was suggested. Aiming
to elucidate the explosion characteristics, we performed the experiments of spherically expandinghydrogen-methane-air lean premixed flames in a closed chamber, where methane was adopted asa representative of flammable organic compounds. At sufficiently small flame radii, smooth flame
surface was observed. The addition of methane to hydrogen-air mixtures generated the increasein the propagation velocity of unstretched flame. At large flame radii, cellular surface induced byintrinsic instability was found, and the flame acceleration was confirmed. The parameters of flame
acceleration model were estimated, and then the flame propagation velocity depending on the
flame radius was predicted. The normalized increment coefficient became larger at low equivalence
ratios, owing to stronger diffusive-thermal instability. Under the same hydrogen concentration, themethane addition generated the increase in the maximum pressure in a closed chamber. The
maximum pressure of experiments was lower than that of calculations, which was because of heatloss during premixed combustion. Under the same methane concentration, the pressure ratio ofexperiments and calculations was lower when the flame propagation velocity was smaller. This was
because of larger heat loss. The obtained results were valuable information to elucidate thehydrogen explosion at Fukushima Daiichi Nuclear Power Station.
61

６．まとめ本事業では、１F１号機及び３号機の原子炉建屋において発生した爆発現象に関して、水素濃度等及び可燃性有機ガスの影響を把握することを目的に、水素及び可燃性有機ガス濃度、初期
ガス温度をパラメータとして、火炎色等確認試験 （拡散燃焼試験）及び予混合燃焼試験を計画し実施した。そして，以下の結果と知見を得た。
（拡散燃焼）
・燃料にメタンが含まれている場合、薄オレンジ色の輝炎が観察されると共に、バーナー出口近傍
では青色の炎が観察される。前者は遊離した炭素から発せられるものであり、後者は CH 発光によるものである。
・燃料が水素のみの場合、薄い赤い炎が観察される。これは暗室における試験において確認されるものであり、屋外では水素火炎を目視で確認することは困難である。
・ガス総流量が大きくなると、最高温度は若干上昇する。また、水素濃度が高い方が、最高温度は高くなる。これは、水素火炎温度の方がメタン火炎温度より高いからである。
・燃料に窒素を添加すると、火炎の色は薄くなり、火炎温度は低下する。
（予混合燃焼）・火炎半径の増加と共に火炎面にセルが形成され、それが発達して複雑な形状になる。セルの形
成は、火炎の固有不安定性によるものである。このセルの形成は従来の燃焼実験[5,9,10]でも観察され、JAEA の研究グループの数値計算[11]においても確認されている。
・水素濃度が高くなると共に、火炎の伝播速度は増大する。これは予混合火炎の燃焼速度が大きくなるからである。また、容器内の最大圧力は上昇する。これは混合気の発熱量が大きくなり、火
炎温度が高くなるからである。
・メタン濃度が高くなると共に、火炎の伝播速度は増大し、容器内の最大圧力は上昇する。前者は予混合火炎の燃焼速度が大きくなることによるもので、後者は火炎温度が高くなることによるものである。
・初期温度が高くなると、火炎の伝播速度は増大する。これは予混合火炎の燃焼速度が大きくなるからである。
・容器内の最大圧力は、水素濃度及びメタン濃度が高くなる（つまり当量比が大きくなる）と共に、
ほぼ単調に上昇する。これは混合気の発熱量が大きくなり、火炎温度が高くなるからである。最大圧力の上昇は、水素爆発による破壊力の強化に結び付くことから、１F の水素爆発における可燃性有機ガスの影響を精査することは非常に重要である。
・容器内圧力変化（時間履歴）の結果を、中間取りまとめ[1]に示されている解析結果と比較し、3号機 3 階天井部の梁の損傷に関して，両者に整合性が有ることを確認した。
・本事業で得られた成果の一部は、英文学術雑誌に掲載されている[12]。
62（今後の展望）
・海外の関連する組織との交流が必要である。フランスの関連組織 ICARE/CNRS は、本事業にも関係するガス爆発の分野において、水蒸気を含めたガスを扱える密閉型容器を用いて実験を遂行しており、世界でもガス爆発特性に関する知見を有する数少ない研究機関の一つである。この研究機関と水素爆発に係わる情報を交換すると共に、共同での水素爆発試験の実施等を検討することが有用である。
・水素-メタン-空気予混合気の燃焼を取り扱っているが、不活性ガスとしての水蒸気や窒素の添加の影響を調べることが必要である。不活性ガス添加に係る知見は、１F の水素爆発のメカニズムを把握し防爆対策を施す上で、非常に重要な情報となる。
・本事業では、実験室レベルでの水素爆発の基本的な現象を観察している。実機等における爆発現象を把握することは、次のステップとなる。その際、スケールの効果を考慮することが肝要である。
上記に加えて、水素及び混合気体燃焼に関する最新知見を収集し、拡散燃焼及び予混合燃焼に関する知見を整理した。これらの知見は、１F 事故における水素爆発のメカニズムを考察する上で、また水素爆発における可燃性有機ガスの影響を精査する上で、有用な情報になるものである。

７．参考文献[1] 原子力規制委員会, 東京電力福島第一原子力発電所事故の調査・分析に係る中間取りまとめ, 2021 年 3 月 5 日, https://www.nra.go.jp/data/000345595.pdf.
[2] 原子力規制委員会, 東京電力福島第一原子力発電所事故の調査・分析に係る中間取りまとめ（2023 年版）, 2023 年 3 月 7 日, https://www.nra.go.jp/data/000425218.pdf，
https://www.nra.go.jp/data/000425219.pdf.
[3] 新岡嵩, 河野通方, 佐藤順一, 燃焼現象の基礎 (2001), p. 180, オーム社.
[4] Williams, F. A., Combustion Theory, Second Edition (1985), p. 349, Addison-Wesley, CA.
[5] Katsumi, T., Kobayashi, H., Aida, T., Aiba, K., Kadowaki, S., Outward propagation velocity andacceleration characteristics in hydrogen-air deflagration, International Journal of Hydrogen
Energy, Vol. 42 (2017), pp. 7360-7365.
[6] Lewis, B. and Elbe, G., Combustion, Flames and Explosions of Gases, Third Edition (1987),
p. 396, Academic Press, Orlando, FL.
[7] Law, C. K., Combustion Physics (2006), p. 41, Cambridge University Press, NY.
[8] Lei, B., Wei, Q., Pang, R., Xiao, J., Kuznetsov，M., Jordan, T., The effect of hydrogen addition
on methane/air explosion characteristics in a 20-L spherical device, Fuel, Vol. 338, 127351(2023).
63

[9] Lamoureux, N., Chaumeix, N., Paillard, C. E., Laminar flame velocity determination for H2air-He-CO2 mixtures using the spherical bomb method, Experimental Thermal and Fluid
Science, Vol. 27 (2003), pp. 385–393.
[10] Okafor, E. C., Hayakawa, A., Nagano, Y., Kitagawa, T., Effects of hydrogen concentration onpremixed laminar flames of hydrogen-methane-air, International Journal of Hydrogen
Energy, Vol. 39, Issue 5 (2014), pp. 2409–2417.
[11] Thwe Thwe Aung, Terada, A., Hino R., Nagaishi, R., and Kadowaki, S., Simulation of the selfpropagating hydrogen-air premixed flame in a closed-vessel by an open-source CFD code,
Journal of Nuclear Science and Technology, Vol. 59, No. 5 (2022), pp. 573-579.
[12] Kadowaki, S., Katsumi, T., Sato, D., Noguchi, H., Zemba, A., Iwanaga, K., Abe, S.,
Characteristics of spherically expanding hydrogen-methane-air lean premixed flames in aclosed chamber: aiming to elucidate the hydrogen explosion at Fukushima Daiichi Nuclear
Power Station, Mechanical Engineering Letters, Vol. 10, 23-00586 (2024).

64本報告書は、原子力規制委員会原子力規制庁からの委託により実施した業務の成果をとりまとめたものです。
本報告書に関する問い合わせは、原子力規制庁までお願いします。