JP4141819B2 - Fuel cell system - Google Patents

Description

【００３１】
外気温度が低い状態、例えば氷点下（−５℃以下等）において燃料電池１１を運転時間ｔ（ｓ）に亘って作動させた際に生成される生成水総量ｍｗ（ｇ）は、水の分子量Ｍｗと、燃料電池１１を構成する電解質電極構造体２４の数（セル数）ｃｅｌｌとにより、例えば下記数式（２）に示すように記述される。
【００３２】
【数２】

【００３３】
ここで、生成水総量ｍｗの水を吸着するために必要とされる吸着材２８の吸着材量ｍａ（ｇ）は、吸着前の吸着率つまりパージ処理実行後における脱離後吸着率θｓと、吸着後における吸着後吸着率θｅと、吸着能γ（＝被吸着物質の飽和重量／吸着材２８の乾燥重量）とにより、例えば下記数式（３）に示すように記述される。
【００３４】
【数３】

【００３５】
例えば、ゼオライトからなる吸着材２８において、ｔ＝２０ｓとし、∫Ｉ・ｄｔ＝５００Ｃとし、ｃｅｌｌ＝４００とし、θｅ＝０．９とし、θｓ＝０．８とし、γ＝０．２とすると、ｍｗ≒２０ｇ、ｍａ≒１ｋｇとなり、燃料電池１１に搭載可能な吸着材２８の量であると判断することができる。
【００３６】
ここで、吸着材２８の吸着率θは、例えば下記数式（４）および図３に示すように、吸着材２８の温度Ｔおよび雰囲気の水蒸気分圧Ｐｗの関数とされる吸着等温曲線により記述される。
なお、図３に示すように、吸着材２８は、温度Ｔが低くなるほど被吸着物質（水）を吸着して水蒸気分圧Ｐｗを低下させ、温度Ｔが高くなるほど被吸着物質（水）を脱離して水蒸気分圧Ｐｗを増大させる。ここで、例えば氷点下（−５℃以下等）等の低温状態において、被吸着物質が吸着されることで吸着材２８の吸着率θが脱離後吸着率θｓから吸着後吸着率θｅへと変化した（例えば、図３に示す矢印Ａ）後に、温度Ｔが燃料電池１１の定格運転温度（例えば、７０〜８０℃程度）まで上昇すると、燃料電池１１のカソード２３は飽和水蒸気圧の状態もしくは飽和水蒸気圧近傍の状態であるため、例えば吸着率θの値は吸着後吸着率θｅに維持される（例えば、図３に示す矢印Ｂ）。そして、燃料電池１１の運転停止後に、温度Ｔが定格運転温度近傍の状態で、相対的に乾燥した空気が燃料電池１１のカソード２３に供給されると、吸着材２８に吸着された水が脱離され、吸着率θの値は脱離後吸着率θｓへと変化する（例えば、図３に示す矢印Ｃ）。
なお、低温状態において、吸着率θが脱離後吸着率θｓから吸着後吸着率θｅへと変化した（例えば、図３に示す矢印Ａ）後に、飽和水蒸気圧未満の状態で温度Ｔが上昇すると、吸着材２８に吸着された水が脱離されることで水蒸気分圧Ｐｗが増大し、吸着率θの値は脱離後吸着率θｓへと変化する（例えば、図３に示す矢印Ｄ）。
【００３７】
【数４】

【００３８】
燃料電池１１のカソード２３は飽和水蒸気圧の状態もしくは飽和水蒸気圧近傍の状態であり、飽和水蒸気圧は温度のみの関数で記述可能であることから、燃料電池１１の運転停止時における停止時水蒸気分圧Ｐｗｅは、例えば下記数式（５）に示すように、燃料電池１１の運転停止以前における運転温度Ｔｅのみにより記述される。
【００３９】
【数５】

【００４０】
上記数式（４），（５）により、燃料電池１１の運転停止時における吸着率θである吸着後吸着率θｅは、例えば下記数式（６）に示すように、燃料電池１１の運転停止以前における運転温度Ｔｅのみの関数となる。
【００４１】
【数６】

【００４２】
ここで、燃料電池１１の運転時におけるカソード２３の全圧力Ｐｔ（ｋＰａ）に対し、水蒸気モル分率Ｘｗは、例えば下記数式（７）に示すように記述され、水蒸気濃度Ｃ（ｐｐｍ）は、例えば下記数式（８）に示すように記述される。
【００４３】
【数７】

【００４４】
【数８】

【００４５】
例えば、燃料電池１１の運転停止時において、Ｔｅ＝９０℃とし、θｅ＝０．８とし、Ｐｔ＝１２０ｋＰａとし、パージ処理においてカソード２３に供給される空気の露点Ｔｄ＝１０℃とすれば、吸着等温曲線を示す適宜の理論式に基づく上記数式（５）により、Ｐｗｅ＝ｆ（９０）≒７０．１ｋＰａとなり、
水蒸気分圧収束値Ｐｗｐ＝ｆ（１０）≒１．２ｋＰａとなる。
さらに、上記数式（７），（８）により、燃料電池１１の運転停止以前における水蒸気濃度Ｃｅ＝１０^６・Ｘｗｅ＝１０^６・Ｐｗｅ／Ｐｔ
＝１０^６×７０．１／１２０＝５．８４×１０^５ｐｐｍとなり、水蒸気濃度収束値Ｃｐ＝１０^６×１．２／１２０＝１０^４ｐｐｍとなる。
【００４６】
パージ処理の実行時には、飽和状態近傍の水蒸気濃度Ｃｅによって燃料電池１１から水蒸気が排出され、水蒸気濃度（例えば、図５におけるカソード流路２６ａの出口水分濃度）および吸着率θは、例えば図５に示すように、吸着等温曲線に沿って低下し、水蒸気濃度収束値Ｃｐに収束するように変化する。この変化の過程における各時刻での水蒸気濃度Ｃｔに対し、（Ｃｔ−Ｃｐ）に相当する水の量が燃料電池１１から除去される。従って、燃料電池１１から除去される水分量ｍｗ’は、パージ処理にて供給される供給空気流量ｎａｉｒ（ｍｏｌ／ｓ）とパージ処理の実行を継続する時間ｔｐとに基づき、例えば下記数式（９）および図４に示すように記述される。
【００４７】
【数９】

【００４８】
これにより、例えば、吸着材２８の吸着材量ｍａ＝１ｋｇかつ供給空気流量ｎａｉｒ＝５ｍ^３／ｍｉｎの場合に、約２０ｇの水を燃料電池１１から除去するためにパージ処理の実行を継続する時間は約６ｓとなる。
【００４９】
一方、燃料電池１１の始動時にカソード２３において生成される生成水総量ｍｗは始動時の温度Ｔに応じて変化する。
このため、吸着材２８により吸着すべき水の必要吸着量は、適宜の熱収支シミュレーションによって理論的に算出可能であると共に、予め測定した始動時の温度Ｔと電流Ｉの時系列データに基づいて実験的に算出可能である。すなわち、複数の異なる始動時の温度Ｔ毎に対して、例えば図６に示すような温度Ｔと電流Ｉの経時変化を検出し、温度Ｔが摂氏０度になるまでの電流積算値（例えば、図６に示す斜線部Ｅ）を算出する。そして、例えば図７に示すような始動時の温度Ｔと電流積算値（∫Ｉ・ｄｔ）との関係を示すマップを作成し、このマップに対するマップ検索により電流積算値を算出し、上記数式（２）により生成水総量ｍｗを算出する。
【００５０】
さらに、パージ処理の実行を継続する時間は実験的に算出可能である。この場合には、先ず、例えば図８に示すような燃料電池１１の始動時の温度に応じた必要とされる吸着材２８の吸着率θ（脱離後吸着率θｓと同等）の変化を示すマップ等に基づき、必要とされる吸着率θを算出する。
次に、例えば図９に示すような燃料電池１１の運転停止以前における運転温度Ｔｅに対する吸着等温線図の水蒸気分圧を露点に変換して得たマップ等に基づき、必要とされる吸着率θに応じた露点を算出する。
そして、複数の異なる運転温度Ｔｅ毎に対し、パージ処理を実行した際のカソード流路２６ａの出口位置での露点の時間変化を検出し、例えば図１０に示すような露点の時間変化のマップ等を作成し、必要とされる露点に対応する時間をパージ処理の実行を継続する時間（パージ時間）とする。
これにより、例えば図１１に示すような燃料電池１１の始動時の温度に応じて変化するパージ時間の運転温度Ｔｅに対する依存性のマップ等に基づきパージ時間を設定することができる。
【００５１】
なお、燃料電池１１の次回の始動時における温度Ｔを推定する際には、例えば、前回の始動時における外気温度のデータや、過去の始動時における外気温度のデータや、今回の走行時における外気温度の時間変化および今回の始動時刻のデータや、今回の始動時における季節のデータや、例えば燃料電池１１を搭載した車両の仕向地やこの車両のナビゲーション装置等において算出される現在位置のデータ等に基づいて推定される温度のうち、最も低い温度を選択する。
さらに、前回の始動時から所定時間以上経過した時点においては、今回の始動時における燃料電池１１の温度（機関温度）を参照して、次回の始動時の温度Ｔを推定してもよい。
【００５２】
例えば、所望の地域の月別の最低気温のデータを記憶装置（図示略）に記憶し、今回の始動時における外気温度および始動時刻を検出し、この始動時刻における最低気温のデータと外気温度の検出値との偏差を算出する。
そして、今月に対して所定期間だけ前後の月における最低気温のデータのうち、最も低い最低気温を抽出し、この抽出した最低気温から偏差を減算して得た値を次回の始動時の温度Ｔとして設定する。
【００５３】
また、今回の始動時における燃料電池１１の温度が、前回の停止時に推定した温度Ｔよりも低く、氷点下である場合には、例えば燃料電池１１の始動時に、少なくとも生成される水を結露させずに水蒸気の状態で外部に排出することができる程度の空気量をカソード２３に供給するセーフモード処理を実行する。
【００５４】
以下に、燃料電池システム１０の始動（起動）時および停止時の動作について説明する。
先ず、図１２に示すステップＳ０１においては、燃料電池１１の運転モードが起動モードか否かを判定する。
この判定結果が「ＮＯ」の場合には、後述するステップＳ０７に進む。
一方、この判定結果が「ＹＥＳ」の場合には、ステップＳ０２に進む。
【００５５】
ステップＳ０２においては、今回の起動モードにおいて検出される温度Ｔ１（例えば、外気温度や、燃料電池１１の冷却水の温度や、燃料電池１１本体の温度等に応じた温度）が所定値＃Ｔ１（例えば、−５℃等）未満か否かを判定する。
この判定結果が「ＮＯ」の場合には、一連の処理を終了する。
一方、この判定結果が「ＹＥＳ」の場合には、ステップＳ０３に進む。
ステップＳ０３においては、パージ処理の実行を指示するパージフラグのフラグ値に「１」を設定する。
【００５６】
次に、ステップＳ０４においては、燃料電池１１の今回の起動後の起動モードにおいて検出される温度Ｔ１の最小値を最小温度Ｔ１’に設定する。
次に、ステップＳ０５においては、最小温度Ｔ１’と、後述するように燃料電池システム１０の前回の作動停止時に設定されて不揮発性メモリ（図示略）に格納された前回温度Ｔ１Ｂとのうち、何れか小さい方の値を、パージ時間算出用の温度Ｔ１”として設定する。
次に、ステップＳ０６においては、パージ時間算出用の温度Ｔ１”に応じて、例えば次回の始動時において検出される温度Ｔ１を推定し、吸着材２８の温度Ｔが、推定した温度Ｔ１から氷点下まで変化する期間中に燃料電池１１の発電により生成される水の量が、吸着材２８にて吸着可能となるまでに要するパージ時間ｔ１を算出し、後述するステップＳ１２に進む。
【００５７】
一方、ステップＳ０７においては、燃料電池１１の今回の起動後において運転時に検出される温度Ｔ２（例えば、外気温度や、燃料電池１１の冷却水の温度や、燃料電池１１本体の温度等に応じた温度）が所定値＃Ｔ２（例えば、−５℃等）未満か否かを判定する。
この判定結果が「ＮＯ」の場合には、後述するステップＳ１２に進む。
一方、この判定結果が「ＹＥＳ」の場合には、ステップＳ０８に進む。
ステップＳ０８においては、パージ処理の実行を指示するパージフラグのフラグ値に「１」を設定する。
【００５８】
次に、ステップＳ０９においては、燃料電池１１の今回の起動後において運転時に検出される温度Ｔ２の最小値を最小温度Ｔ２’に設定する。
次に、ステップＳ１０においては、最小温度Ｔ２’と、後述するように燃料電池システム１０の前回の作動停止時に設定されて不揮発性メモリ（図示略）に格納された前回温度Ｔ２Ｂとのうち、何れか小さい方の値を、パージ時間算出用の温度Ｔ２”として設定する。
次に、ステップＳ１１においては、パージ時間算出用の温度Ｔ２”に応じて、例えば吸着材２８の温度Ｔが上述したステップＳ１０にて推定した温度Ｔ２から氷点下まで変化する期間中に燃料電池１１の発電により生成される水の量が、吸着材２８にて吸着可能となるまでに要するパージ時間ｔ２を、例えば上述した図１１等に基づいて算出する。
【００５９】
そして、ステップＳ１２においては、燃料電池１１の運転モードが停止モードか否かを判定する。
この判定結果が「ＮＯ」の場合には、一連の処理を終了する。
一方、この判定結果が「ＹＥＳ」の場合には、ステップＳ１３に進む。
【００６０】
ステップＳ１３においては、パージフラグのフラグ値に「１」が設定されているか否かを判定する。
この判定結果が「ＹＥＳ」の場合には、後述するステップＳ１６に進む。
一方、この判定結果が「ＮＯ」の場合には、ステップＳ１４に進む。
ステップＳ１４においては、燃料電池１１の今回の起動後において検出される温度Ｔ１を、燃料電池１１の次回の起動時に利用する前回温度Ｔ１Ｂとして設定し、燃料電池１１の今回の起動後において運転時に検出される温度Ｔ２を、燃料電池１１の次回の起動後において利用する前回温度Ｔ２Ｂとして設定し、各前回温度Ｔ１Ｂ，Ｔ２Ｂを不揮発性メモリ（図示略）に格納し、ステップＳ１５に進む。
そして、ステップＳ１５においては、燃料電池システム１０の作動を停止して、一連の処理を終了する。
【００６１】
一方、ステップＳ１６においては、パージ時間ｔ１と、パージ時間ｔ２とのうち、何れか大きい方の値を、所定時間ｔ３として設定する。
そして、ステップＳ１７においては、所定時間ｔ３に亘ってパージ処理を実行する。
次に、ステップＳ１８においては、燃料電池１１の今回の起動後において設定された最小温度Ｔ１’を、燃料電池１１の次回の起動時に利用する前回温度Ｔ１Ｂとして設定し、燃料電池１１の今回の起動後において運転時に設定された最小温度Ｔ２’を、燃料電池１１の次回の起動後において利用する前回温度Ｔ２Ｂとして設定し、各前回温度Ｔ１Ｂ，Ｔ２Ｂを不揮発性メモリ（図示略）に格納する。
そして、ステップＳ１９においては、パージフラグのフラグ値に「０」を設定し、上述したステップＳ１５に進む。
【００６２】
すなわち、燃料電池システム１０の運転停止時には、次回の始動時に備えて、吸着材２８の吸着率θが所定の値となるようにパージ処理を実行する。ここで、パージ処理を実行する時間は、例えば、外気温度や燃料電池１１の冷却水の温度や燃料電池１１本体の温度等に応じた起動モードの最小温度Ｔ１’および運転時の最小温度Ｔ２’に応じて設定される各パージ時間ｔ１，ｔ２のうち、何れか大きい方の値を設定する。
【００６３】
上述したように、本実施の形態による燃料電池システム１０によれば、低温状態、例えば氷点下（−５℃以下等）における燃料電池１１の始動時であっても、発電により生成される生成水を吸着材２８により確実に吸着させることができ、例えばカソード流路２６ａやガス拡散層２３ｂで生成水が凍結してしまうことを防止し、燃料電池１１の発電を適切に継続させることができる。
さらに、燃料電池１１の次回の始動時に備えて吸着材２８の吸着率θを所定の値に設定するパージ処理において、予め低温状態での始動時に吸着すべき水の必要吸着量とパージ時間との関係を示す演算式やテーブル等をシミュレーションや実験に基づき設定することにより、効率良くパージ処理を実行することができる。
しかも、燃料電池１１の内部に配置された吸着材２８が水を吸着する際に吸着熱を発生することによって、低温状態の燃料電池１１の温度を所定温度（例えば、定格運転温度）まで上昇させるのに要する時間を短縮することができる。
【００６４】
なお、上述した本実施の形態においては、複数の粒子状の吸着材２８，…，２８が固体高分子電解質膜２１のカソード側の表面部に分散配置されているとしたが、これに限定されず、例えば図１３に示す本実施形態の第１変形例に係る燃料電池セル２７のように、複数の粒子状の吸着材２８，…，２８をカソード側のガス拡散層２３ｂ内に分散配置させてもよい。
また、例えば図１４に示す本実施形態の第２変形例に係る燃料電池セル２７のように、複数の粒子状の吸着材２８，…，２８をカソード流路２６ａ内に分散配置させてもよい。
さらに、例えば図１５に示す本実施形態の第３変形例に係る燃料電池セル２７のように、複数の粒子状の吸着材２８，…，２８をカソード側のガス拡散層２３ｂの表面部に分散配置させ、各吸着材２８，…，２８の表面上の適宜の領域がカソード流路２６ａ内に露出するようにしてもよい。
【００６５】
なお、本実施の形態においては、複数の粒子状の吸着材２８，…，２８を燃料電池１１内に配置するとしたが、これに限定されず、例えば、ゼオライトや、シリカゲルや、活性アルミナや、活性炭等からなり、反応ガスが流通可能な複数の気孔を有するシート状や板状等の吸着層を燃料電池セル２７のカソード側に設けてもよい。
【００６６】
なお、本実施の形態においては、燃料電池システム１０の作動停止時において、燃料電池１１の次回の始動時における温度Ｔを推定してパージ処理を実行するとしたが、これに限定されず、例えば車両停止時に各温度検出器１９ａ，１９ｂ，１９ｃから出力される検出信号に基づいて、適宜のタイミングでパージ処理を実行してもよい。
【００６７】
なお、本実施の形態においては、カソード加湿器１３および加湿器バイパス流路３５を省略してもよい。
【００６８】
【発明の効果】
以上説明したように、本発明の燃料電池システムによれば、氷点下において燃料電池が始動される場合であっても、発電により生成される水を吸着材によって確実に吸着させることができ、例えば生成される水の凍結によって反応ガスのガス流路や拡散層が閉塞されてしまうことを防止して、燃料電池の発電を適切に継続させることができる。
さらに、請求項３に記載の燃料電池システムによれば、氷点下において燃料電池を始動させる際の生成水量算出手段の算出精度を向上させることができ、脱離実行手段を効率よく実行させることができる。
【００６９】
さらに、請求項４に記載の燃料電池システムによれば、吸着材に比べて相対的に乾燥した気体を酸素極に供給することによって、吸着材に吸着された水を容易に脱離させることができる。
さらに、請求項５に記載の燃料電池システムによれば、燃料電池の発電により生成される水を効率よく吸着させることができる。
【００７０】
さらに、請求項６に記載の燃料電池システムによれば、燃料電池の発電により生成した水の吸着および脱離を効率よく行うことができると共に、燃料電池の温度を上昇させる際の温度上昇率を、吸着材による水の吸着によって発生する熱により向上させることができる。
さらに、請求項７に記載の燃料電池システムによれば、発電により生成される水を吸着材によって確実に吸着させることができると共に、燃料電池の大きさや重量が過剰に増大することを抑制することができる。
【図面の簡単な説明】
【図１】 本発明の一実施形態に係る燃料電池システムの構成図である。
【図２】 図１に示す燃料電池の構成を示す断面図である。
【図３】 吸着材の吸着率と吸着材の雰囲気における水蒸気分圧との関係を示す吸着等温線のグラフ図である。
【図４】 パージ処理の実行を継続する時間に応じた水蒸気濃度の変化を示すグラフ図である。
【図５】 パージ処理の実行前後における水蒸気濃度および吸着率の各計算値の時間変化を示すグラフ図である。
【図６】 燃料電池の発電時における電流と温度の変化を示すグラフ図である。
【図７】 燃料電池の始動時の温度に応じて変化する電流積算値の変化を示すグラフ図である。
【図８】 燃料電池の始動時の温度に応じて変化する必要とされる吸着材の吸着率の変化を示すグラフ図である。
【図９】 吸着材の吸着率と吸着材の雰囲気の露点との関係を示す吸着等温線のグラフ図である。
【図１０】 パージ処理の実行を継続する時間に応じた露点の変化を示すグラフ図である。
【図１１】 燃料電池の始動時の温度に応じて変化するパージ時間の燃料電池の運転温度に対する依存性を示すグラフ図である。
【図１２】 燃料電池システムの始動時および停止時の動作を示すフローチャートである。
【図１３】 本実施形態の第１変形例に係る燃料電池の構成を示す断面図である。
【図１４】 本実施形態の第２変形例に係る燃料電池の構成を示す断面図である。
【図１５】 本実施形態の第３変形例に係る燃料電池の構成を示す断面図である。
【符号の説明】
１０ 燃料電池システム
２２ アノード（燃料極）
２３ カソード（酸素極）
１９ａ 吸気温度検出器（温度検出手段）
１９ｂ 機関温度検出器（温度検出手段）
１９ｃ 媒体温度検出器（温度検出手段）
ステップＳ０６ 温度推定手段
ステップＳ０６、ステップＳ１１ 継続時間設定手段
ステップＳ１３ 脱離判定手段
ステップＳ１７ 脱離実行手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system including a fuel cell such as a solid polymer membrane fuel cell.
[0002]
[Prior art]
Conventionally, for example, a polymer electrolyte membrane fuel cell is configured by stacking a plurality of cells on a cell formed by sandwiching a polymer electrolyte membrane between a fuel electrode (anode) and an oxygen electrode (cathode) from both sides. A stack (hereinafter referred to as a fuel cell) is supplied with hydrogen as a fuel to the fuel electrode, air is supplied as an oxidant to the oxygen electrode, and hydrogen ions generated by a catalytic reaction at the fuel electrode, It passes through the solid polymer electrolyte membrane, moves to the oxygen electrode, and causes an electrochemical reaction with oxygen at the oxygen electrode to generate power.
By the way, in the fuel cell system including such a fuel cell, when the power generation operation of the fuel cell is started in a state where the outside air temperature is low, for example, below the freezing point (−5 ° C. or lower), the generated water generated by the power generation is solidified. As a result, the gas flow path and the diffusion layer of the reaction gas are blocked, and it may be difficult to continue power generation.
Conventionally, for example, the fuel cell is heated by an electric heater or the like, the heated coolant is supplied to the fuel cell, or the exothermic reaction of hydrogen and oxygen on the cathode catalyst or the anode catalyst. A method (for example, refer to Patent Document 1) is known.
[0003]
[Patent Document 1]
JP 2001-189164 A
[0004]
[Problems to be solved by the invention]
However, as in the fuel cell system according to the above prior art, when the temperature around the power generation unit of the fuel cell is raised from a low temperature state such as below freezing point to a temperature of 0 ° C or higher at which the frozen state is eliminated. Since the amount of heat required for this temperature increase increases with the heat capacity of the fuel cell, the time required for this temperature increase may be relatively long.
Here, for example, when the fuel cell system is mounted as a driving power source for a vehicle such as a fuel cell vehicle, the time required from when the ignition switch of the vehicle is turned on until the fuel cell can generate power, That is, there is a possibility that convenience may deteriorate due to a long time required for the vehicle to start.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a fuel cell system capable of continuing the power generation operation of the fuel cell even in a low temperature state such as below freezing point.
[0005]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object, the fuel cell system of the present invention according to claim 1 is a fuel electrode sandwiching a solid polymer electrolyte membrane from both sides (for example, the anode 22 in the present embodiment). And an oxygen electrode (for example, the cathode 23 in the present embodiment), as a reaction gas, a fuel containing hydrogen is supplied to the fuel electrode, an oxidant containing oxygen is supplied to the oxygen electrode, and an electrochemical reaction A fuel cell that generates electricity, an adsorbent disposed inside the fuel cell and capable of adsorbing and desorbing water, at least an environmental temperature related to a temperature around the fuel cell, a temperature of the fuel cell body, and the fuel Temperature detecting means for detecting any of the temperature of the cooling medium that cools the battery (for example, the intake air temperature detector 19a, the engine temperature detector 19b, the medium temperature detector 19c in the present embodiment), and Based on the detection result of the degree detecting means, The next start will be below freezing and determine whether it is necessary to adsorb water generated by power generation, According to the desorption determination means (for example, step S13 in the present embodiment) for determining whether or not water is desorbed from the adsorbent, and the determination result by the desorption determination means, When the fuel cell is stopped Desorption executing means for desorbing water from the adsorbent (for example, step S17 in the present embodiment) is provided.
[0006]
Furthermore, the fuel cell system of the present invention according to claim 2 provides the fuel cell. The next Temperature detected by the temperature detecting means at start-up Temperature estimation means for estimating the temperature estimated by the temperature estimation means Generated water amount calculating means (for example, Equation (2) in the present embodiment) for calculating the amount of water generated by power generation of the fuel cell over a period in which the temperature changes from a predetermined temperature below the freezing point to the freezing point, and the generation Based on the amount of water calculated by the water amount calculation unit and the temperature detected by the temperature detection unit when the determination process by the desorption determination unit is executed, a time for continuing the desorption execution unit is set. Continuation time setting means (for example, step S06 and step S11 in the present embodiment).
[0007]
Furthermore, the fuel cell system of the present invention according to claim 2 is characterized in that the power generation of the fuel cell is performed over a period in which the temperature detected by the temperature detecting means at the start of the fuel cell changes from a predetermined temperature below the freezing point to the freezing point. Generated water amount calculating means (for example, Equation (2) in the present embodiment), the amount of water calculated by the generated water amount calculating means, and the desorption determining means. Based on the temperature detected by the temperature detection means at the time of execution of the determination process, duration setting means for setting a time for continuing execution of the desorption execution means (for example, step S06 and step S11 in the present embodiment) It is characterized by comprising.
[0008]
According to the fuel cell system configured as described above, the duration setting unit detects the state of the adsorbent at this time based on, for example, the temperature detected by the temperature detection unit when the determination process by the desorption determination unit is executed. At the same time, the state of the adsorbent capable of adsorbing the amount of water calculated by the generated water amount calculating means is set, and the time for continuing the execution of the desorption executing means required to reach this set state is set. .
Thereby, the water produced | generated by electric power generation can be reliably adsorb | sucked with an adsorbent, the freezing of the produced | generated water can be prevented, and the electric power generation of a fuel cell can be continued appropriately.
[0010]
According to the fuel cell system configured as described above, the temperature estimation means includes, for example, temperature data detected by the temperature detection means at the previous start or at the past start, or the temperature detection means at the time of operation of the current fuel cell system. The temperature detected by the temperature detecting means at the next start of the fuel cell is estimated on the basis of the time change data of the temperature detected by the above and the data on the season and region at the time of the current start.
Thereby, the calculation accuracy of the generated water amount calculation means when starting the fuel cell below freezing point can be improved, and the desorption execution means can be executed efficiently.
[0011]
further, Claim 3 In the fuel cell system according to the present invention, the desorption executing means supplies a gas having a water vapor partial pressure equal to or lower than a predetermined partial pressure (for example, air in the present embodiment) to the oxygen electrode. .
[0012]
According to the fuel cell system having the above-described configuration, the desorption executing means supplies the adsorbent by supplying a gas whose water vapor partial pressure is equal to or lower than a predetermined partial pressure and relatively dry compared to the adsorbent to the oxygen electrode. The water adsorbed on can be easily desorbed.
[0013]
further, Claim 4 In the fuel cell system according to the present invention, the adsorbent is at least in the vicinity of the oxygen electrode and the oxygen electrode of the solid polymer electrolyte membrane. When It is characterized by being arranged in any of these.
[0014]
According to the fuel cell system having the above configuration, the water generated by the power generation of the fuel cell can be efficiently adsorbed by arranging the adsorbent in the vicinity of the catalyst constituting the oxygen electrode. Here, the vicinity of the catalyst constituting the oxygen electrode is, for example, the oxygen electrode side of the solid polymer electrolyte membrane, the gas diffusion layer constituting the oxygen electrode, the gas flow path of the reaction gas on the oxygen electrode side, etc. Yes.
[0015]
further, Claim 5 In the fuel cell system according to the present invention, the adsorbent is Generates heat due to water adsorption It is characterized by comprising at least one of zeolite, silica gel, activated alumina, and activated carbon.
[0016]
According to the fuel cell system having the above configuration, the adsorbent is composed of at least one of zeolite, silica gel, activated alumina, and activated carbon, thereby efficiently adsorbing and desorbing water generated by power generation of the fuel cell. It can be performed well, and the rate of temperature increase when the temperature of the fuel cell is raised to a predetermined temperature (for example, the rated operating temperature of the fuel cell) at the start of the fuel cell, etc. is generated by adsorption of water by the adsorbent It can be improved by heat.
[0017]
further, Claim 6 In the fuel cell system according to the present invention, the amount of the adsorbent is an amount capable of adsorbing at least the amount of water calculated by the generated water amount calculation means.
[0018]
According to the fuel cell system configured as described above, at least the amount of adsorbent that can adsorb the amount of water calculated by the generated water amount calculating means is disposed inside the fuel cell, so that water generated by power generation is adsorbed. As a result, the fuel cell can be reliably adsorbed and an excessive increase in the size and weight of the fuel cell can be suppressed.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a fuel cell system of the present invention will be described with reference to the accompanying drawings.
A fuel cell system 10 according to the present embodiment is mounted as a power source for driving in a fuel cell vehicle, for example, and as shown in FIG. 1, a fuel cell 11, an air compressor 12, a cathode humidifier 13, and a humidifier. A bypass switch valve 14, a fuel supply device 15, an ejector 16, a cooler 17, a control device 18, an intake air temperature detector 19a, an engine temperature detector 19b, and a medium temperature detector 19c are provided. It is configured.
[0020]
For example, as shown in FIG. 2, the fuel cell 11 includes a solid polymer electrolyte membrane (membrane) 21 made of a cation exchange membrane, a fuel electrode (anode) 22 made of an anode catalyst 22a and a gas diffusion layer 22b, and a cathode. An electrolyte electrode structure 24 sandwiched between an oxygen electrode (cathode) 23 composed of a catalyst 23a and a gas diffusion layer 23b, and a plurality of fuel cell cells 27 sandwiched between a pair of separators 25 and 26 are laminated. It is configured.
A concave groove is formed on the surface of each separator 25, 26 facing the electrolyte electrode structure 24, and an anode channel 25 a and a cathode channel 26 a are formed by each concave groove and the electrolyte electrode structure 24. Has been.
[0021]
Further, the fuel cell 11 includes an adsorbent 28 capable of adsorbing and desorbing water. For example, a plurality of particulate adsorbents 28,..., 28 are provided on the surface of the solid polymer electrolyte membrane 21 on the cathode side. Distributed.
The adsorbent 28 includes, for example, at least one of zeolite, silica gel, activated alumina, activated carbon, and the like, and is, for example, zeolite.
Further, the total amount of the adsorbents 28,..., 28 is, for example, at least when the fuel cell 11 is started below freezing point, for example, the environmental temperature (for example, the outside air temperature) related to the temperature around the fuel cell 11 or the temperature of the fuel cell 11. (Engine temperature), the temperature of the cooling medium of the fuel cell 11, the temperature of the adsorbents 28,..., 28, etc. are generated by the power generation of the fuel cell 11 over a period in which the temperature changes from a predetermined temperature below the freezing point to the freezing point. The amount of water is the amount that can be adsorbed.
[0022]
Fuel gas (reactive gas) such as hydrogen is supplied to the anode 22 of the fuel cell 11 from an inlet side pipe 31 connected to the anode flow path 25a, and hydrogen ionized by a catalytic reaction on the anode catalyst 22a of the anode 22 Moves to the cathode 23 through the moderately humidified solid polymer electrolyte membrane 21, and electrons generated by this movement are taken out to an external circuit (not shown) and used as direct current electric energy. . For example, air, which is an oxidant gas (reactive gas) containing oxygen, is supplied to the cathode 23 from an inlet-side pipe 32 connected to the cathode channel 26a, and hydrogen ions, electrons, and oxygen react at the cathode 23. Water is generated. Then, exhaust gas containing unreacted reaction gas is discharged outside the fuel cell 11 from the outlet side pipe 33 connected to the anode flow path 25a and the outlet side pipe 34 connected to the cathode flow path 26a.
[0023]
The air compressor 12 takes in air from the outside of the vehicle, for example, adiabatically compresses it, and supplies this air as a reaction gas to the cathode 23 of the fuel cell 11 via the cathode humidifier 13.
The cathode humidifier 13 ensures the ionic conductivity of the solid molecular electrolyte membrane 21 of the fuel cell 11 in a predetermined state by humidifying the air supplied to the cathode 23 of the fuel cell 11.
A humidifier bypass flow path 35 that bypasses the cathode humidifier 13 is provided via the humidifier bypass switching valve 14 in the flow path that connects the air compressor 12, the cathode humidifier 13, and the inlet side pipe 32 on the cathode 23 side. It has been.
That is, the air whose temperature has been compressed by the air compressor 12 is changed via the cathode humidifier 13 or the cathode by switching the flow path in the humidifier bypass switching valve 14 according to the operating state of the fuel cell 11, for example. It is supplied to the cathode 23 of the fuel cell 11 without going through the humidifier 13.
[0024]
The fuel supply device 15 includes, for example, a high-pressure hydrogen tank, and a pneumatic proportional pressure control valve that discharges hydrogen at a predetermined pressure using the pressure of air supplied from the air compressor 12 as a signal pressure. The hydrogen supplied from the fuel supply device 15 is circulated through the ejector 16 to the inlet side piping 31 on the anode 22 side of the fuel cell 11.
The ejector 16 is supplied from the fuel supply device 15 and is discharged from the outlet-side pipe 33 on the anode side of the fuel cell 11 that is sub-flowed by the negative pressure generated in the vicinity of the high-speed hydrogen gas flow that circulates inside. The exhaust gas is mixed with hydrogen supplied from the fuel supply device 15 and supplied again to the fuel cell 11 to circulate the exhaust gas discharged from the fuel cell 11.
[0025]
Further, a medium flow path (not shown) in which a cooling medium supplied from the outside circulates is provided inside the fuel cell 11, and a circulation pump 17a and a heat exchanger that circulate the cooling medium in the medium flow path. A cooler 17 is configured with 17b. That is, the cooling medium supplied to the medium flow path of the fuel cell 11 via the circulation pump 17a is returned to the circulation pump 17a again after heat exchange in the process of flowing through the heat exchanger 17b. .
[0026]
For example, the control device 18 calculates a command value for the rotational speed of the air compressor 12 according to the driving state of the vehicle, and controls the operation of the air compressor 12 according to the command value, thereby generating the power generation state of the fuel cell 11. To control.
Further, the control device 18 is connected to the air compressor 12 from the air compressor 12 for a predetermined time to be described later, for example, when the fuel supply shutoff valve 15a provided in the fuel supply device 15 stops the fuel supply to the fuel cell 11. The humidifier bypass switching valve 14 and the air compressor 12 are controlled so that the supplied air flows through the humidifier bypass channel 35 and is supplied to the cathode 23 of the fuel cell 11 without passing through the cathode humidifier 13. As a result, the relatively humid air that bypasses the cathode humidifier 13 is supplied to the cathode 23 of the fuel cell 11, whereby a predetermined amount of the water adsorbed on the adsorbent 28 is desorbed, and the adsorbent 28. Is set to a predetermined value.
[0027]
Here, the control device 18 sets a predetermined time for supplying relatively dry air to the cathode 23 of the fuel cell 11, for example, an environmental temperature (for example, an outside air temperature) related to the temperature around the fuel cell 11, a fuel The temperature is set based on the temperature of the battery 11 (engine temperature), the temperature of the cooling medium of the fuel cell 11, and the like.
For this reason, the control device 18 includes, for example, a detection signal output from the intake air temperature detector 19 a that detects the temperature of the air taken into the air compressor 12 (intake air temperature), and the engine temperature that detects the temperature of the fuel cell 11. The detection signal output from the detector 19b and the detection signal output from the medium temperature detector 19c that detects the temperature of the cooling medium discharged from the medium flow path of the fuel cell 11 are input.
[0028]
The fuel cell system 10 according to the present embodiment has the above-described configuration. Next, the water adsorbed by the adsorbent 28 during the operation of the fuel cell system 10, particularly when the operation of the fuel cell 11 is stopped, for example. Desorption processing (purge processing) will be described with reference to the attached drawings.
[0029]
Hereinafter, a process of setting a time for continuing the purge process will be described.
The amount of generated water nw (mol / s) generated at the cathode 23 during power generation of the fuel cell 11 is calculated by, for example, the following formula using current I (A) taken out to an external circuit (not shown) and Faraday constant F by power generation. It is described as shown in (1).
[0030]
[Expression 1]

[0031]
The generated water total amount mw (g) generated when the fuel cell 11 is operated over the operating time t (s) in a state where the outside air temperature is low, for example, below freezing (such as −5 ° C. or less) is the molecular weight Mw of water. And the number (cell number) cell of the electrolyte electrode structures 24 constituting the fuel cell 11, for example, as shown in the following mathematical formula (2).
[0032]
[Expression 2]

[0033]
Here, the adsorbent amount ma (g) of the adsorbent 28 required for adsorbing the water of the total amount of generated water mw is the adsorption rate before adsorption, that is, the adsorption rate θs after desorption after execution of the purge process, The post-adsorption adsorption rate θe after the adsorption and the adsorption capacity γ (= saturated weight of the substance to be adsorbed / dry weight of the adsorbent 28) are described, for example, as shown in the following formula (3).
[0034]
[Equation 3]

[0035]
For example, in the adsorbent 28 made of zeolite, when t = 20 s, ∫I · dt = 500 C, cell = 400, θe = 0.9, θs = 0.8, and γ = 0.2, Since mw≈20 g and ma≈1 kg, it can be determined that the amount of the adsorbent 28 that can be mounted on the fuel cell 11.
[0036]
Here, the adsorption rate θ of the adsorbent 28 is described by an adsorption isothermal curve that is a function of the temperature T of the adsorbent 28 and the water vapor partial pressure Pw of the atmosphere, for example, as shown in the following formula (4) and FIG. The
As shown in FIG. 3, the adsorbent 28 adsorbs the substance to be adsorbed (water) as the temperature T becomes lower, lowers the water vapor partial pressure Pw, and desorbs the substance to be adsorbed (water) as the temperature T becomes higher. Increase the water vapor partial pressure Pw. Here, the adsorption rate θ of the adsorbent 28 changes from the post-desorption adsorption rate θs to the post-adsorption adsorption rate θe due to the adsorption of the adsorbed substance in a low temperature state such as below freezing point (−5 ° C. or lower). When the temperature T rises to the rated operating temperature (for example, about 70 to 80 ° C.) of the fuel cell 11 after (for example, the arrow A shown in FIG. 3), the cathode 23 of the fuel cell 11 is saturated or saturated. Since the state is near the water vapor pressure, for example, the value of the adsorption rate θ is maintained at the post-adsorption adsorption rate θe (for example, arrow B shown in FIG. 3). Then, after the operation of the fuel cell 11 is stopped, when the relatively dry air is supplied to the cathode 23 of the fuel cell 11 in a state where the temperature T is near the rated operation temperature, the water adsorbed on the adsorbent 28 is removed. The adsorption rate θ changes to a post-desorption adsorption rate θs (for example, arrow C shown in FIG. 3).
In the low temperature state, when the adsorption rate θ changes from the post-desorption adsorption rate θs to the post-adsorption adsorption rate θe (for example, arrow A shown in FIG. 3), the temperature T rises below the saturated water vapor pressure. As the water adsorbed on the adsorbent 28 is desorbed, the water vapor partial pressure Pw increases, and the value of the adsorption rate θ changes to the post-desorption adsorption rate θs (for example, arrow D shown in FIG. 3).
[0037]
[Expression 4]

[0038]
The cathode 23 of the fuel cell 11 is in the state of saturated water vapor pressure or in the vicinity of the saturated water vapor pressure, and the saturated water vapor pressure can be described by a function of temperature alone. The pressure Pwe is described only by the operation temperature Te before the operation of the fuel cell 11 is stopped, for example, as shown in the following formula (5).
[0039]
[Equation 5]

[0040]
From the above formulas (4) and (5), the post-adsorption adsorption rate θe, which is the adsorption rate θ when the fuel cell 11 is stopped, is obtained before the fuel cell 11 is stopped, for example, as shown in the following formula (6). It is a function of the operating temperature Te only.
[0041]
[Formula 6]

[0042]
Here, with respect to the total pressure Pt (kPa) of the cathode 23 during operation of the fuel cell 11, the water vapor molar fraction Xw is described as shown in the following formula (7), for example, and the water vapor concentration C (ppm) is For example, it is described as shown in the following formula (8).
[0043]
[Expression 7]

[0044]
[Equation 8]

[0045]
For example, when Te = 90 ° C., θe = 0.8, Pt = 120 kPa, and the dew point Td = 10 ° C. of the air supplied to the cathode 23 in the purge process when the fuel cell 11 is shut down, the adsorption is performed. From the above formula (5) based on an appropriate theoretical formula showing an isothermal curve, Pwe = f (90) ≈70.1 kPa,
The water vapor partial pressure convergence value Pwp = f (10) ≈1.2 kPa.
Further, according to the above formulas (7) and (8), the water vapor concentration Ce = 10 before the operation of the fuel cell 11 is stopped. ⁶ ・ Xwe = 10 ⁶ ・ Pwe / Pt
= 10 ⁶ × 70.1 / 120 = 5.84 × 10 ⁵ ppm, water vapor concentration convergence value Cp = 10 ⁶ × 1.2 / 120 = 10 ⁴ ppm.
[0046]
When the purge process is executed, the water vapor is discharged from the fuel cell 11 by the water vapor concentration Ce in the vicinity of the saturated state, and the water vapor concentration (for example, the outlet water concentration of the cathode channel 26a in FIG. 5) and the adsorption rate θ are shown in FIG. As shown, it decreases along the adsorption isotherm curve and changes to converge to the water vapor concentration convergence value Cp. The amount of water corresponding to (Ct−Cp) is removed from the fuel cell 11 with respect to the water vapor concentration Ct at each time in the process of this change. Accordingly, the amount of water mw ′ removed from the fuel cell 11 is based on, for example, the following mathematical formula (9) based on the supply air flow rate nair (mol / s) supplied in the purge process and the time tp during which the purge process is continued. ) And as shown in FIG.
[0047]
[Equation 9]

[0048]
Thereby, for example, the adsorbent amount ma = 1 kg and the supply air flow rate nair = 5 m of the adsorbent 28. ³ In the case of / min, the time for which the purge process is continued to remove about 20 g of water from the fuel cell 11 is about 6 s.
[0049]
On the other hand, the total amount of generated water mw generated at the cathode 23 at the start of the fuel cell 11 changes according to the temperature T at the start.
For this reason, the necessary amount of water to be adsorbed by the adsorbent 28 can be theoretically calculated by an appropriate heat balance simulation, and based on time series data of the temperature T and current I measured in advance. It can be calculated experimentally. That is, for each of a plurality of different starting temperatures T, for example, a change with time in temperature T and current I as shown in FIG. 6 is detected, and an integrated current value until the temperature T reaches 0 degrees Celsius (for example, A hatched portion E) shown in FIG. 6 is calculated. Then, for example, a map showing the relationship between the starting temperature T and the current integrated value (∫I · dt) as shown in FIG. 7 is created, and the current integrated value is calculated by searching the map, and the above formula ( The total generated water mw is calculated by 2).
[0050]
Furthermore, the time for which the purge process is continued can be calculated experimentally. In this case, first, a change in the adsorption rate θ (equivalent to the adsorption rate θs after desorption) of the adsorbent 28 required according to the temperature at the start of the fuel cell 11 as shown in FIG. 8, for example, is shown. Based on the map or the like, the required adsorption rate θ is calculated.
Next, for example, based on a map obtained by converting the water vapor partial pressure in the adsorption isotherm with respect to the operating temperature Te before the operation stop of the fuel cell 11 as shown in FIG. Calculate the dew point according to.
Then, the time change of the dew point at the outlet position of the cathode channel 26a when the purge process is executed for each of a plurality of different operating temperatures Te is detected, for example, a map of the time change of the dew point as shown in FIG. The time corresponding to the required dew point is defined as the time for continuing the purge process (purge time).
Accordingly, the purge time can be set based on, for example, a map of the dependence of the purge time on the operating temperature Te, which varies depending on the temperature at the start of the fuel cell 11 as shown in FIG.
[0051]
When estimating the temperature T at the next start-up of the fuel cell 11, for example, data on the outside air temperature at the previous start-up, data on the outside air temperature at the past start-up, or outside air at the current travel time Temporal change in temperature and data of the current start time, seasonal data at the time of the current start, data on the current position calculated by, for example, the destination of the vehicle on which the fuel cell 11 is mounted, the navigation device of the vehicle, etc. The lowest temperature is selected from the temperatures estimated based on the above.
Furthermore, when a predetermined time or more has elapsed since the previous start, the temperature T at the next start may be estimated with reference to the temperature (engine temperature) of the fuel cell 11 at the current start.
[0052]
For example, the monthly minimum temperature data for a desired region is stored in a storage device (not shown), the outside air temperature and the start time at the current start are detected, and the minimum temperature data and the outside air temperature at the start time are detected. The deviation from the value is calculated.
Then, the lowest minimum temperature is extracted from the minimum temperature data in the months preceding and following this month for a predetermined period, and the value obtained by subtracting the deviation from the extracted minimum temperature is the temperature T at the next start. Set as.
[0053]
Further, when the temperature of the fuel cell 11 at the time of the current start is lower than the temperature T estimated at the previous stop and below the freezing point, for example, at the time of starting the fuel cell 11, at least the generated water is not condensed. Then, a safe mode process is performed in which an amount of air that can be discharged to the outside in the state of water vapor is supplied to the cathode 23.
[0054]
Hereinafter, operations at the time of starting (starting) and stopping of the fuel cell system 10 will be described.
First, in step S01 shown in FIG. 12, it is determined whether or not the operation mode of the fuel cell 11 is the startup mode.
If this determination is “NO”, the flow proceeds to step S 07 described later.
On the other hand, if this determination is “YES”, the flow proceeds to step S 02.
[0055]
In step S02, the temperature T1 detected in the current start mode (for example, the temperature according to the outside air temperature, the temperature of the cooling water of the fuel cell 11, the temperature of the main body of the fuel cell 11, etc.) is a predetermined value # T1 ( For example, it is determined whether the temperature is less than −5 ° C. or the like.
When the determination result is “NO”, the series of processes is terminated.
On the other hand, if the determination is “YES”, the flow proceeds to step S03.
In step S03, “1” is set to the flag value of the purge flag instructing execution of the purge process.
[0056]
Next, in step S04, the minimum value of the temperature T1 detected in the startup mode after the current startup of the fuel cell 11 is set to the minimum temperature T1 ′.
Next, in step S05, any one of the minimum temperature T1 ′ and the previous temperature T1B set when the fuel cell system 10 was previously stopped and stored in a non-volatile memory (not shown) as will be described later. The smaller value is set as the purge time calculation temperature T1 ″.
Next, in step S06, the temperature T1 detected at the next start, for example, is estimated according to the temperature T1 ″ for calculating the purge time, and the temperature T of the adsorbent 28 is from the estimated temperature T1 to below the freezing point. Calculating the purge time t1 required for the amount of water generated by the power generation of the fuel cell 11 to be adsorbed by the adsorbent 28 during the changing period; Proceed to step S12 to be described later .
[0057]
On the other hand, in step S07, the temperature T2 detected during operation after the current startup of the fuel cell 11 (for example, the outside air temperature, the temperature of the cooling water of the fuel cell 11, the temperature of the fuel cell 11 main body, etc.) It is determined whether or not (temperature) is less than a predetermined value # T2 (for example, −5 ° C., etc.)
If this determination is “NO”, the flow proceeds to step S 12 described later.
On the other hand, if the determination is “YES”, the flow proceeds to step S08.
In step S08, "1" is set to the flag value of the purge flag that instructs execution of the purge process.
[0058]
Next, in step S09, the minimum value of the temperature T2 detected during operation after the current startup of the fuel cell 11 is set to the minimum temperature T2 ′.
Next, in step S10, any one of the minimum temperature T2 ′ and the previous temperature T2B that was set when the fuel cell system 10 was previously stopped and stored in a non-volatile memory (not shown), as will be described later, The smaller value is set as the purge time calculation temperature T2 ″.
Next, in step S11, for example, the temperature T of the adsorbent 28 is described above according to the temperature T2 ″ for calculating the purge time. Step S10 Estimated by Temperature T2 The purge time t2 required for the amount of water generated by the power generation of the fuel cell 11 to be adsorbed by the adsorbent 28 during the period from the freezing point to below the freezing point is calculated based on, for example, FIG. .
[0059]
In step S12, it is determined whether or not the operation mode of the fuel cell 11 is the stop mode.
When the determination result is “NO”, the series of processes is terminated.
On the other hand, if the determination is “YES”, the flow proceeds to step S13.
[0060]
In step S13, it is determined whether or not “1” is set in the flag value of the purge flag.
If this determination is “YES”, the flow proceeds to step S 16 described later.
On the other hand, if this determination is “NO”, the flow proceeds to step S14.
In step S14, the temperature T1 detected after the current activation of the fuel cell 11 is set as the previous temperature T1B used at the next activation of the fuel cell 11, and detected during operation after the current activation of the fuel cell 11. The temperature T2 to be used is set as the previous temperature T2B to be used after the next activation of the fuel cell 11, the previous temperatures T1B and T2B are stored in a nonvolatile memory (not shown), and the process proceeds to step S15.
In step S15, the operation of the fuel cell system 10 is stopped, and the series of processes is terminated.
[0061]
On the other hand, in step S16, the larger one of the purge time t1 and the purge time t2 is set as the predetermined time t3.
In step S17, the purge process is executed for a predetermined time t3.
Next, in step S18, the minimum temperature T1 ′ set after the current activation of the fuel cell 11 is set as the previous temperature T1B used at the next activation of the fuel cell 11, and the current activation of the fuel cell 11 is performed. The minimum temperature T2 ′ set later during operation is set as the previous temperature T2B to be used after the next activation of the fuel cell 11, and the previous temperatures T1B and T2B are stored in a nonvolatile memory (not shown).
In step S19, the flag value of the purge flag is set to “0”, and the process proceeds to step S15 described above.
[0062]
That is, when the operation of the fuel cell system 10 is stopped, the purge process is executed so that the adsorption rate θ of the adsorbent 28 becomes a predetermined value in preparation for the next start-up. Here, the time for executing the purge processing is, for example, the minimum temperature T1 ′ in the start mode and the minimum temperature T2 ′ in operation according to the outside air temperature, the temperature of the cooling water of the fuel cell 11, the temperature of the main body of the fuel cell 11, etc. The larger one of the purge times t1 and t2 set in accordance with is set.
[0063]
As described above, according to the fuel cell system 10 according to the present embodiment, even when the fuel cell 11 is started at a low temperature, for example, below freezing point (−5 ° C. or lower), the generated water generated by the power generation is reduced. The adsorbent 28 can reliably adsorb, and for example, the generated water can be prevented from freezing in the cathode channel 26a and the gas diffusion layer 23b, and the power generation of the fuel cell 11 can be appropriately continued.
Further, in a purge process in which the adsorption rate θ of the adsorbent 28 is set to a predetermined value in preparation for the next start-up of the fuel cell 11, the required adsorption amount of water to be adsorbed at the start-up in the low temperature state and the purge time By setting an arithmetic expression, a table, etc. indicating the relationship based on simulations and experiments, the purge process can be executed efficiently.
In addition, the adsorbent 28 disposed inside the fuel cell 11 generates heat of adsorption when adsorbing water, thereby raising the temperature of the fuel cell 11 in a low temperature state to a predetermined temperature (for example, a rated operating temperature). The time required for this can be shortened.
[0064]
In the above-described embodiment, the plurality of particulate adsorbents 28,..., 28 are distributed and arranged on the surface of the solid polymer electrolyte membrane 21 on the cathode side. Instead, a plurality of particulate adsorbents 28,..., 28 are dispersed and arranged in the cathode-side gas diffusion layer 23b as in the fuel cell 27 according to the first modification of the present embodiment shown in FIG. May be.
Further, for example, a plurality of particulate adsorbents 28,..., 28 may be dispersedly arranged in the cathode channel 26a as in the fuel cell 27 according to the second modification of the present embodiment shown in FIG. .
Further, as in a fuel cell 27 according to a third modification of the present embodiment shown in FIG. 15, for example, a plurality of particulate adsorbents 28,..., 28 are dispersed on the surface of the cathode-side gas diffusion layer 23b. An appropriate region on the surface of each adsorbent 28,..., 28 may be exposed in the cathode channel 26a.
[0065]
In the present embodiment, the plurality of particulate adsorbents 28,..., 28 are arranged in the fuel cell 11. However, the present invention is not limited to this. For example, zeolite, silica gel, activated alumina, An adsorption layer made of activated carbon or the like and having a plurality of pores through which the reaction gas can flow may be provided on the cathode side of the fuel cell 27.
[0066]
In the present embodiment, when the operation of the fuel cell system 10 is stopped, the purge process is executed by estimating the temperature T at the next start of the fuel cell 11, but the present invention is not limited to this. The purge process may be executed at an appropriate timing based on the detection signals output from the temperature detectors 19a, 19b, and 19c during the stop.
[0067]
In the present embodiment, the cathode humidifier 13 and the humidifier bypass channel 35 may be omitted.
[0068]
【The invention's effect】
As described above, according to the fuel cell system of the present invention, even when the fuel cell is started below freezing point, water generated by power generation can be reliably adsorbed by the adsorbent, for example, generation Thus, it is possible to prevent the gas flow path and the diffusion layer of the reaction gas from being blocked by the freezing of the water, and to continue the power generation of the fuel cell appropriately.
Furthermore, according to the fuel cell system of the third aspect, the calculation accuracy of the generated water amount calculating means when starting the fuel cell below freezing can be improved, and the desorption executing means can be executed efficiently. .
[0069]
Furthermore, according to the fuel cell system of the fourth aspect, the water adsorbed on the adsorbent can be easily desorbed by supplying a relatively dry gas compared to the adsorbent to the oxygen electrode. it can.
Furthermore, according to the fuel cell system of claim 5, water generated by power generation of the fuel cell can be adsorbed efficiently.
[0070]
Furthermore, according to the fuel cell system of the sixth aspect, the water generated by the power generation of the fuel cell can be adsorbed and desorbed efficiently, and the rate of temperature increase when the temperature of the fuel cell is raised is increased. The heat generated by the adsorption of water by the adsorbent can be improved.
Furthermore, according to the fuel cell system of claim 7, water generated by power generation can be reliably adsorbed by the adsorbent, and the increase in size and weight of the fuel cell is suppressed. Can do.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a fuel cell system according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing the configuration of the fuel cell shown in FIG.
FIG. 3 is a graph of an adsorption isotherm showing the relationship between the adsorption rate of the adsorbent and the water vapor partial pressure in the atmosphere of the adsorbent.
FIG. 4 is a graph showing a change in water vapor concentration according to the time for which the execution of the purge process is continued.
FIG. 5 is a graph showing temporal changes in respective calculated values of water vapor concentration and adsorption rate before and after execution of a purge process.
FIG. 6 is a graph showing changes in current and temperature during power generation by the fuel cell.
FIG. 7 is a graph showing a change in an integrated current value that changes in accordance with the temperature at the start of the fuel cell.
FIG. 8 is a graph showing the change in the adsorption rate of the adsorbent that needs to change according to the temperature at the start of the fuel cell.
FIG. 9 is a graph of an adsorption isotherm showing the relationship between the adsorption rate of the adsorbent and the dew point of the atmosphere of the adsorbent.
FIG. 10 is a graph showing a change in the dew point according to the time for which the execution of the purge process is continued.
FIG. 11 is a graph showing the dependence of the purge time, which varies depending on the temperature at the start of the fuel cell, on the operating temperature of the fuel cell.
FIG. 12 is a flowchart showing operations at the start and stop of the fuel cell system.
FIG. 13 is a cross-sectional view showing a configuration of a fuel cell according to a first modification of the present embodiment.
FIG. 14 is a cross-sectional view showing a configuration of a fuel cell according to a second modification of the present embodiment.
FIG. 15 is a cross-sectional view showing a configuration of a fuel cell according to a third modification of the present embodiment.
[Explanation of symbols]
10 Fuel cell system
22 Anode (fuel electrode)
23 Cathode (oxygen electrode)
19a Intake air temperature detector (temperature detection means)
19b Engine temperature detector (temperature detection means)
19c Medium temperature detector (temperature detection means)
Step S06 Temperature estimation means
Step S06, Step S11 Duration setting means
Step S13 Desorption determination means
Step S17 Desorption execution means

Claims (6)

It has a fuel electrode and an oxygen electrode sandwiching the solid polymer electrolyte membrane from both sides, and as a reaction gas, a fuel containing hydrogen is supplied to the fuel electrode, an oxidant containing oxygen is supplied to the oxygen electrode, and an electrochemical reaction A fuel cell that generates electricity,
An adsorbent disposed inside the fuel cell and capable of adsorbing and desorbing water;
Temperature detection means for detecting at least one of an environmental temperature related to a temperature around the fuel cell, a temperature of the fuel cell main body, and a temperature of a cooling medium that cools the fuel cell;
Based on the detection result of the temperature detection means, the next start is below freezing point, it is determined whether or not it is necessary to adsorb water generated by power generation, and whether or not water is desorbed from the adsorbent. Desorption determination means for determining
A fuel cell system comprising : a desorption execution unit that desorbs water from the adsorbent when the fuel cell is stopped according to a determination result by the desorption determination unit. Temperature estimating means for estimating a temperature detected by the temperature detecting means at the next start-up of the fuel cell, and the fuel over a period in which the temperature estimated by the temperature estimating means changes from a predetermined temperature below the freezing point to the freezing point. Generated water amount calculating means for calculating the amount of water generated by power generation of the battery;
Time for continuing execution of the desorption execution unit based on the amount of water calculated by the generated water amount calculation unit and the temperature detected by the temperature detection unit when the determination process by the desorption determination unit is performed The fuel cell system according to claim 1, further comprising: a duration setting unit that sets 3. The fuel cell system according to claim 1, wherein the desorption executing unit supplies a gas having a water vapor partial pressure equal to or lower than a predetermined partial pressure to the oxygen electrode . 4. The adsorbent according to claim 1 , wherein the adsorbent is disposed at least in one of the oxygen electrode and the vicinity of the oxygen electrode of the solid polymer electrolyte membrane . 5. Fuel cell system. The fuel cell system according to any one of claims 1 to 4, wherein the adsorbent is composed of at least one of zeolite, silica gel, activated alumina, and activated carbon that generates heat by adsorption of water. . Wherein the amount of adsorbent, fuel cell system according to claim 2, characterized in that the amount capable of adsorbing an amount of the water is calculated by at least the amount of produced water calculating means.

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