| 摘要: | 根據環保署2013 年的統計，交通排放所產生的PM2.5 以及NOX 為人為產生源最高的污染源，甚至超過工業排放。而根據交通部統計，機車為國人使用頻率最高的運具，直至2018 年年底數量已多達約1400 萬輛。而目前使用中且超過5年之機車，每年均須至定檢站進行排氣定期檢驗，確保排放符合標準，然而，檢測項目僅針對HC 以及CO 兩種污染物做檢驗，當中並沒有量測粒狀污染物，表示目前使用中機車粒狀物的排放是未知的，因此，本研究的主要目的是為機車排放粒狀物開發一種精確、快速與穩定的氣膠採樣和測量方法，並評估當前機車定期排氣檢定之有效性。實驗以裝置PM2.5 分徑器的採樣管進行機車排氣採樣，該分徑器浸於冰浴槽中，再依後端各量測儀器特性決定是否須進行稀釋量測。污染物分別在不同的行駛條件（加速、固定轉速、怠速與市區行車型態）下量測，氣狀物包括CO、HC、CO2、SO2、VOC、NOX 以及O2，粒狀物包括不透光度、黑碳質量濃度、微粒數目濃度、微粒質量濃度，微粒粒徑分布。氣體污染物主要受加速的影響。顆粒濃度隨著引擎轉速的增加而增加。含氧感知器故障會導致空燃比不穩定，並造成引擎的運行處於閉環狀態，從而導致CO，NOX 和HC 的濃度升高。排氣汽門間隙的增加會導致較高的HC 和顆粒物濃度，這可能是由於未燃燒的油氣洩漏所致。微粒數目濃度隨速度增加而增加。而黑碳和PM2.5 質量濃度僅在引擎轉速較高時才會顯示有效的測量值。因此，它們可能是篩選較嚴重污染者的理想選擇。應重新評估檢查和維護項目，以找出可能導致更高排放的因素。電子噴射引擎建議提高含氧感知器的檢查頻率和汽門間隙。根據本研究進行的測試，在機車部分功能異常時的HC 以及CO 排放濃度仍遠低於定檢之規範值，表示排放標準可能太寬鬆，但由於測試之車輛樣本較少，仍須更多的相關研究才能進一步探討。;Motorcycle is the most popular transportation tool in Taiwan. Periodic emission test is performed to ensure that all motorcycles conforms to EPA regulations governing emissions. So far, the particulate matter is not included in the emission test. Therefore, the main purpose of the present study is to develop a precise, rapid and stable aerosol sampling and measurement method for motorcycle emission. This study also aims to evaluate the effectiveness of the current motorcycle emission test program.
The motorcycle exhaust exiting the tailpipe is drawn into a sampling train with a PM2.5 separator which is immersed in an iced bath. The cooled exhaust is then either measured directly by gas/PM sensors, or through a diluter if the concentration is too high for the sensors. The gas (CO, HC, CO2, SO2, VOC, NOX, O2) and particulate (opacity, black carbon, particle number, particle mass, size distribution) real-time emissions are evaluated in different driving cycle (acceleration, fixed, idle and urban driving cycle).
The gas pollutants are mainly affected by the rate of acceleration, and show a slight increase in high speed. The particle concentration increases with increasing acceleration rate and speed. The oxygen sensor failure causes unstable air-fuel ratio, and the engine operation apparently is not in closed loop, causing the concentrations of CO, NOX and HC to rise. An increase in the exhaust valve clearance results in higher HC and particulate concentrations, probably due to the leaking of unburned oil and gas. Particle number increases with increasing speed. The black carbon and PM meters show valid measurement values only when the speed is high. Therefore, they might be ideal for screening heavy polluters. The inspection and maintenance items should be re-evaluated to identify the major factors that might cause higher emissions. The higher inspecting frequency of oxygen sensor and valve clearance is recommended. Yet, the emission standards are too loose based on the tests conducted in this work. |
