The Studies of Channel Pressure on the Ignition Mechanism of High-Pressure Hydrogen Release

[[abstract]]氫氣普遍應用於石化、光電、半導體等產業，作為還原劑，氫氣也是最乾淨的能源，其燃燒僅產生水，無任何溫室氣體。 氫氣本身並非自燃性氣體，但根據Wolanski 與Wojcicki [1972]以震波管(shock tube)排放高壓氫氣至空氣中結果得知，氫氣及氧氣的界面會產生引燃，其推論原因為絕熱壓縮導致氣體溫度上升，而產生自燃現象。Kim et al [2013]以兩塊耐壓玻璃所製成的排放管進行試驗，並以兩台高速攝影機觀測紀錄破裂盤後的氫氣流場證實震波壓縮導致引燃。而後Chen et al [2013]相似於近似於Kim et al [2013]的系統，以近似於意外事故中的長型裂縫，觀察紀錄破裂盤後的氫氣流場。由於Chen et al [2013]的結果中發現震波有不同之現象，因此擬加裝壓力計，觀察其排放管內之壓力變化，並與震波結構做比對。 測試結果分為無引燃、引燃但管外無持續火焰及引燃但管外有持續火焰，由無引燃及引燃但管外有持續火焰之壓力數據比較，產生引燃現象需有一定之震波強度。但因排放管之限制，而無法清楚得知排放管入口引燃的條件，但比較兩種不同之引燃現象，可發現引燃但管外有持續火焰之狀況在排放管中間所量測到的壓力會先達到一高峰而後再衰減，但引燃而管外無持續火焰之狀況則無此壓力高峰，此壓力高峰並與管內最大升壓速率相關聯，推論此壓力高峰應與火焰強度相關，間接證明管內火焰強度是決定管外是否引燃的最重要因素，此結果有助於瞭解氫氣外洩自燃的機制。[[abstract]]Hydrogen is commonly used in the petrochemical semiconductor and optoelectronic plants as a reducing agent It is also the cleanest fuel which produces only water upon combustion and no other greenhouse gases Hydrogen is not a pyrophoric gas However Wolanski and Wojcicki's [1972] used a shock tube to release hydrogen into and observed autoignition in the contact surface of hydrogen and air It is suspected that adiabatic compression leading to temperature rise caused the ignition Kim et al [2013] studied the shock and flow structure inside the flow channel with the aids of double glass window and two high speed cameras and confirmed that shock compression was the cause of ignition Chen et al [2013] used a similar system as those of Kim et al [2013] but with a rectangular channel that similar to real cracks to record the shock wave and shock structure Different shock structure was observed in the rectangular channels Thus it is intended to measure the pressure inside the channel and to compare with the shock structure The results can be classified into no ignition; ignition but without jet flame outside the channel and ignition with jet flame outside the channel The condition of ignition inside the channel cannot be resolved properly owing to the limitation from the channel Comparing the two cases with ignition it is found that the pressure inside the channel will reach a peak and then decay for the case of sustained jet flame outside channel For the cases without jet flame outside the channel the pressure spike was absent The pressure spike is also found to relate to the maximum pressure rise rate Thus it is suspected that the pressure spike is related to the flame intensity which provides an indirect evidence for proving that the ignition and jet flame outside the channel is decided by the flame intensity inside the channel The results will help to better understand the ignition behavior of hydrogen releas