改變點火正時探討沼氣發電機燃燒穩定性及其性能

Abstract

論文在台中月眉台糖養豬場測試30kW沼氣發電機。研究計畫其一，為了提高引擎效率，安裝除濕機以祛除沼氣中多餘的水分，此外量測除濕後沼氣的確切成分及其相對應之濃度。計畫其二，安裝完整之點火系統，包括火星塞式壓力感測器、旋轉編碼器及點火正時訊號擷取。實驗結果顯示，在沼氣除濕後發電功率明顯提升；在沼氣供給量為220L/min時，沼氣除濕後發電功率比未除濕之沼氣提高5.9%。本發電機最佳點火正時為BTDC13度，在此角度下操作引擎可以達到最大之發電功率以及熱效率，同時其燃燒穩定性也較穩定(CoVIMEP較小)。提前點火或延後點火，除了發電功率及熱效率下降以外，亦使燃燒穩定性變差(CoVIMEP較大)。另外，實驗發現燃燒越穩定，沼氣甲烷使用率越高，反之亦然。

This study tested a 30kW-generator in a small biogas plant in Taiwan Sugar swine farm in Taichung. The biogas after desulfurization process still contains the water vapor. Hence, it is necessary to remove the water vapor in the intake biogas before it is fueled into the engine. In this study, the first work is to dehumidify the water vapor in intake biogas. In addition to these, the detailed intake biogas constitutes and their concentrations are also measured in order to get the real data. Secondly, install a complete ignition system, consisting spark plugs pressure sensor and rotary encoder, to record the in-cylinder pressure and crank angle of piston cylinder. In the present study, the engine power output of dehumidified biogas provides up to 5.9% with respective to the humid biogas at biogas supply rate of 220L/min at excess air ratio λ=1. Besides, the optimum spark timing of present engine locates at BTDC13 degree, where supply the highest power generation and thermal efficiency. Delaying or advancing the optimum spark timing leads to poorer power outputs. The spark timing of BTDC13 has lower coefficient of variation in indicated mean effective pressure (CoVIMEP) than delayed and advanced ones, where engine performs more stable indicated mean effect pressure (IMEP) during combustion. In addition, it found that the lower CoVIMEP makes the higher CH4 consumption ratio.