低熱值燃料應用於環型微渦輪引擎之實驗分析與數值模擬

Abstract

為了嶄新的世代，要解決石化燃料短缺危機與符合環保規範減量二氧化碳的生成，再生能源的利用與新興能源的開發已經成為政府極力發展的能源政策，本論文透過數值模擬與實驗分析檢驗了低熱值燃料應用於擁有環型燃燒室之微渦輪引擎的可行性，研究中使用已開發完成的燃油氣渦輪引擎MW54作為載具，並將其以燃油為燃料的燃燒室重新改裝成為適合低熱值生質能氣體燃料之微渦輪引擎燃燒系統， 本論文包含三個部份，第一部分，本論文透過實驗分析，了解低熱值燃料應用於擁有環型燃燒室之微渦輪引擎所能產生的效能。首先為微渦輪引擎架設相關的驅動與感測裝置來完成研究用測試平台。研究中使用不同比例的CO2混合甲烷做為實驗用的低熱值燃料，透過量測得到的數據來分析與評估此引擎的效能。實驗結果顯示，微渦輪引擎最低可使用60% 甲烷含量的燃料來運轉，而使用90% 甲烷燃料時，發電量在85,000轉時達到170W，且70% 甲烷燃料可在60,000轉達到70W。當使用60% 甲烷燃料時，微渦輪引擎所能產生之動力相當的低。微渦輪引擎的布雷登循環效率與發電效率可透過實驗數據的計算得知，最高分別是23% 與10%。 第二部分為透過套裝軟體CFD-ACE+的應用完成了環狀微渦輪引擎在供應低熱值的燃料下，燃燒室襯孔對於燃燒室內熱流場的冷卻效應與環狀微渦輪引擎內的燃燒行為之數值模擬。分析的內容包括環狀微渦輪引擎內的流動特性、燃燒行為、熱傳導分析、化學反應與彼此之間的交互作用。模擬的結果顯示從稀釋區進入的空氣充分的發揮冷卻的效用，而此燃燒室的設計在使用低熱值燃料時，並不會在襯桶壁上產生熱點且排氣溫度都低於排氣溫度的最大容許溫度800°C。 第三部分為未來工作的先前研究，包括了微渦輪引擎的系統鑑別。透過實驗收集整合的數據，可以幫助我們鑑別控制系統內模擬模型的參數，系統鑑別的工作是未來設計控制系統時所必備的。本論文完成了一個使用再生性生質氣體的分散式發電系統，本系統體積小、低成本、維修容易且適合推廣於家庭用。

The utilization of renewable energy and development of new energy sources are the present governmental energy policy to cope with the more and more stringent shortage of fossil fuels and environmental regulations for carbon dioxide reduction in the new century. This dissertation examines the practicability of low-heating value (LHV) fuel on an annular micro gas turbine (MGT) through experimental evaluations and numerical simulations. The MGT used in this study is MW-54, whose original fuel is liquid (Jet A1). Its fuel supply system was re-designed to use biogas fuel with LHV. There are three parts in this dissertation. In the first part, experiments were completed to evaluate the combustion efficiency of an annular MGT while applying the LHV fuel. The corresponding sensors and actuators for the MGT were established to form our test stand. The methane was mixed with different ratio of CO2 to be our LHV fuel. The measured data indicating the engine performance were analyzed and evaluated. Experimental results showed that the presented MGT system operated successfully under each tested condition when the minimum heating value of the simulated fuel was approximately 60% of pure methane. The power output was around 170W at 85,000 RPM as 90% CH4 with 10% CO2 was used and 70W at 60,000 RPM as 70% CH4 with 30% CO2 was used. When a critical limit of 60% CH4 was used, the power output was extremely low. Furthermore, the best theoretical Brayton cycle efficiency and electric efficiency of the MGT were calculated as 23% and 10%, respectively. Following the experiments, the corresponding simulations, aided by the commercial code CFD-ACE+, were carried out to investigate the cooling effect in a perforated combustion chamber and combustion behavior in an annular MGT when using LHV gas. The investigation was conducted to realize the characteristics of the flow, combustion, heat transfer, chemical reaction, and their interactions in an annular MGT. The results confirmed that the cool air flows through dilution holes on combustor liners were functioning fully and there were no hot spots occurred in the liners. In addition, the exhaust temperatures of combustion chamber were lower than 1073K when MGT was operated under different conditions. Finally, the system identification of MGT was completed for future studies. The model identification process is prerequisite for controller design research in the near future. The measured data helped us identify the parameters of dynamic model in numerical simulation. This dissertation presents a novel distributed power supply system that can utilize renewable biogas. The completed micro biogas power supply system is small, low cost, easy to maintain and suited to household use.