Novel Bluff-Body on Improving Temperature Uniformity and Combustion Efficiency of Non-Premixed Flame

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基本資料

Project title

Code/計畫編號

MOST105-2221-E019-038

Translated Name/計畫中文名

新式鈍體提升非預混火焰溫度均勻性及燃燒效率之分析

Project Coordinator/計畫主持人

Shun-Chang Yen

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Mechanical and Mechatronic Engineering

Website

https://www.grb.gov.tw/search/planDetail?id=11885623

Year

2016

Start date/計畫起

01-08-2016

Expected Completion/計畫迄

01-07-2017

Bugetid/研究經費

611千元

ResearchField/研究領域

機械工程

"本計畫書擬議一個系統性的實驗方法，利用星芒狀鈍體調控機制，進行被動式控制非預混式燃燒爐的燃燒效能提升之研究。申請人基於先前對於非預混式燃燒爐的冷流、燃燒效率的多種鈍體被動控制、聲波激擾主動控制等方式的研究與實務經驗。發現紊流擾動、及適量的旋流效果能產生可加速燃料與空氣混合，進而增加燃燒能力。但亦發現三個弱點，第一為非預混式燃燒爐燃燒時，當冷的燃料氣體是以大量快速注入燃燒場時，燃料氣體滯留時間短，燃料氣體和空氣沒有足夠時間完成化學反應，致使火焰上飄離噴口，產生火焰的不穩定性。第二為燃料噴流與鈍體機構間會產生停滯鞍點 (stagnation-saddle point)的流場，對燃料與空氣的混合與燃燒有相當的影響。第三為當旋流機制過大時，熱的火焰燃氣與周圍的冷空氣快速混合，旋渦火焰卻也因此容易造成燃燒反應中斷，而衍生大量的CO 產生，這是旋渦火焰的一大問題；這缺點起因是燃燒時冷的空氣與熱的火焰，因溫度場的不均勻性所衍生的影響。因此本計畫將嘗試，如能以「技術發展」層面的觀點，發展星芒狀調控機構，裝置在傳統的燃燒爐的出口處。將預混式燃燒爐因燃料與空氣滯留時間短所產生的火焰不穩定性、燃料噴流對鈍體停滯鞍點的影響、旋流機制過大時冷熱氣體易造成燃燒反應中斷等，溫度場不均勻性影響因素最小化。預期達到以星芒狀鈍體機構，快速、經濟的增進燃燒效率及降低碳氫化合物污染，其結果在能源節約與環境污染上有極高的價值與應用性。實際例子如:工業用燃燒器、燃汽渦輪機、或民生用瓦斯爐、熱水器等都是有如此需求。有鑑於此，在此專題研究計畫中；第一年: 等溫流場，以星芒狀調控器的機構置於中心燃料噴嘴 (central fuel jet)出口處，及受膛線化噴嘴所導引的環空氣噴流(annular air jet)的旋流條件下，進行冷流場的調制噴流研究。鈍體機構設計包含:不同星芒型(三芒、六芒、圓型)鈍體，搭配中心內切圓與燃料噴嘴直徑比(d/Dc)、與長度比(H/Dc)的錐狀體；嘗試在不同的幾何配置與中心燃料噴流、環空氣噴流條件下，調制非預混式燃燒爐燃燒的流場特性。過程中將以煙線流場可視化技術、LDV 量測系統、拓樸理論的分析應用、熱線風速儀、追蹤氣體濃度量測等交互應用。探討受鈍體控制下，冷流場流動行為、鈍體控制幾何配置選取、速度特性、紊動特性、平均與動態特性、非穩態流動以及混合效果等。煙線流場可視化技術將用來觀測低雷諾數下巨觀的流體行為；LDV 系統以量化的量測流場的平均速度場特性，瞭解流場的結構、與紊流性質；運用臨界點理論之拓樸學的分析，確定複雜的流場結構模態；熱線風速儀將用以偵測旋渦尾流與剪流層中的頻率特性及高低頻之間的相關聯；利用濃度量測儀擷取 CO2 的濃度值，經由追蹤CO2 的濃度分佈瞭解混合的效果。第二年: 燃燒場，繼而將第一年星芒狀控制器在冷流場的研究結果，應用於非預混式燃燒爐中。藉由拍照攝影、Schlieren 光學技術、PIV 量測系統、熱電偶溫度量測、及燃燒氣體濃度分析等實驗方法，研究星芒狀控制器調制非預混燃燒爐時的火焰行為、火焰長度、燃燒場的速度、溫度分佈、燃燒特性與氣體濃度分析等變化。拍照攝影觀察火焰形狀的目的，可由火焰外觀判讀空燃比之間增減對火焰行為的影響。Schlieren 光學技術可擷取噴嘴出口附近流場的密度在空間中一次微分的影像，可清楚觀看噴嘴出口下游凝聚性旋渦尾流結構的輪廓。PIV 系統藉由光學濾鏡的輔助將火焰光譜濾掉，可量化的量測時間相關的火焰非穩態流場之演化過程，以及與渦旋逸放之交互作用。以熱電偶探針進行溫度的量測，得到燃燒場的溫度分佈，並計算燃燒放率，用以判斷火焰模態對燃燒的效應。氣體濃度分析可測的燃燒後氣體的組成包含一氧化碳、二氧化碳、碳氫化合物與氮氧化物，用以瞭解改善燃燒是否完全。" "This project proposes systematic experimental methods to modulate and improve the combustion efficiency of a non-premixed combustor using the astral-shaped disk controller. The applicant has experimentally studied the cold-flow behavior of the non-premixed combustor, the improvement of combustion efficiency using passive bluff-body control and active acoustic-excitation modulation. The experimental results show that the turbulent disturbance and appropriate swirl flow can enhance the mixing of fuel and airflow, and then improve the combustion capacity. However, the previous research experimental experience also showed three weaknesses. Firstly, for the non-premixed combustion process, when the central cold fuel flew fast and massively into the flame field (i.e., at high central fuel-jet speed), an unstable lift-off flame occurred due to the short residence time of fuel flow. This short residence time caused an incomplete chemical combustion reaction between the fuel and air flows. Secondly, the three-way stagnation-saddle points occurred between the fuel jet and bluff body has a considerably effect on the combustion and mixing of fuel and air jets. Thirdly, at high swirl-flow speed, the rapid mixing occurred between the hot flame and ambient cold air. The swirling flame can interrupt the combustion reaction and caused a large generation of carbon monoxide. The cold air and hot flame forms an un-uniform temperature field. This project attempts to minimize the effect of un-uniform temperature field on the flame field by improving the flame instability resulting from the short residence time of fuel and air, by improving the swirling flame between the fuel and bluff body, and by decreasing the occurrence of combustion interrupt at high swirling speed. Finally, this project attempts to design an astral-shaped bluff mechanism for lowering the generation/pollution of hydrocarbon and improving the combustion efficiency behind a non-premixed combustor. Furthermore, the research results will be applied in the issues of energy-saving and environmental pollution, such as the industrial burner, gas turbine, gas stove and gas heater. This project presents a two-year program. In the first year program, this project focuses on the isothermal flow field. An astral-shaped disk controller will be installed at the exit of central fuel jet. Furthermore, this program also considers the effect of swirled annular air jet (i.e., induced using the rifled mechanism). The bluff-body modulators include the astral-shaped controller such as three-astral, six-astral, and circle types. The geometrical parameters include the diameter ratio of central fuel-jet and inscribed bluff disk. The measurement and visualization methods include the smoke streak visualization, laser Doppler velocimeter (LDV), topological analysis, hot-wire anemometry and gas analyzer. Under the controllable parameters of bluff astral-shaped disk, the test/measure properties include the relative size/position of geometrical entities, flow behaviors, velocity characteristics, turbulent properties, averaged and instantaneous flow behaviors, instable flow characteristics and mixing ratio of fuel and air. The smoke strake visualization macroscopically observes the flow behaviors at low Reynolds numbers. The LDV quantitatively measures the averaged velocity field, and then reveals the flow structures and turbulent properties. The topological analysis utilizes the critical point theory to verify the intricate flow characteristics. The hot-wire anemometry measures the frequency features of wake vortex and shear flow, and then build the relationships between the wake-flow structures and typical frequencies. The gas analyzer measures the concentrations of CO2 and then conjectures the mixing result using the concentration distribution of CO2. In the second year program, this project concentrates on the flame field. The fuel will be ignited and burned to verify the controlling parameters obtained in the first year on the flame characteristics. The experimental methods/techniques utilized in the second program include the direct photo, Schlieren optical visualization, PIV, thermocouple measurement and burned exhausted gas analysis. The examination focuses are flame behavior, flame length, velocity contour of flame field, flame temperature distribution, combustion characteristics and exhausted gas distribution. The photographed flame configurations can verify the effect of air/fuel ration on flame behaviors. The Schlieren photograph utilized the first differential image to visualize the coherent structure of wake vortex. The PIV method utilizes the optical filter to remove the flame spectrum and quantize the evolution process of the unsteady flame field. The thermocouple detects the temperature distribution of flame field. The combustion capacity will be considered using these flame temperature distributions. The gas analyze detects the exhausted gas including the carbon monoxide, carbon dioxide, hydrocarbon and nitrogen oxide to improve the combustion completeness."

Keyword(s)

星芒狀調控器
非預混式燃燒爐
等溫流場
燃燒場
Astral-shaped disk controller
Non-premixed combustor
Isothermal flow field
Flame field

DSpace CRIS

Novel Bluff-Body on Improving Temperature Uniformity and Combustion Efficiency of Non-Premixed Flame

基本資料

Description