A Design and Analysis of Novel Non-Premixed Dual-Swirling Combustion Nozzle

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Project title

Code/計畫編號

NSC98-2221-E019-040-MY3

Translated Name/計畫中文名

新式非預混雙旋流燃燒噴嘴設計與分析

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=2204010

Year

2011

Start date/計畫起

01-08-2011

Expected Completion/計畫迄

01-07-2012

Bugetid/研究經費

711千元

ResearchField/研究領域

機械工程

"本計劃書擬議一個系統性的實驗方法，利用鈍體控制機構及聲波激擾等主、被動流控制方式，進行調制旋噴流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、燃燒效率的研究與實務經驗，發現燃料與空氣混合程度，決定了燃燒能力與燃燒後氣體的組成。因此可藉由各種不同的旋流產生方式，加速燃料與空氣混合。本計畫在嘗試，如能以「應用」層面的觀點，發展以簡易的鈍體控制機構，結合膛線化噴嘴的設計及製造技術，裝置在傳統的燃燒爐的出口處，能在不需更改原有設備下，更快速、經濟的增進燃燒效率及降低碳氫化合物污染，相信在能源節約與環境污染的上有極高的價值與應用。有鑑於此，在此專題研究計畫中；第一年中，以“太極型”鈍體控制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)的雙旋流條件下，形成非預混雙旋流噴嘴，進行冷流場的調制旋噴流研究。建立一套可以改變鈍體控制機構的相對高度，及系統性幾何配置的機制，嘗試在各種不同的幾何配置與中心燃料噴流、環旋空氣噴流條件下，調制“太極型”鈍體與旋渦尾流(Swirling vortical wake)的性質。過程中將以煙線流場可視化技術、PIV 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，以尋找出最佳化的設計規則與操作條件，並探討受鈍體控制與不同旋流強度下，所調控的冷流場流動行為、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，並界定出最佳化的設計規則與操作條件；PIV 系統以量化的量測時間相關的非穩態流之演化過程以及與漩渦尾流之交互作用；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。並將混合的效果回溯給“太極型”鈍體的流動控制機構，促使旋渦尾流性質的「可調控性」機制成立。俾利下一年度計畫，應用於中心燃料噴流受鈍體控制及環旋空氣噴流受膛線化噴嘴，雙旋流調制的燃燒爐中使用。表C011 共4頁第 2頁第二年中，繼而將第一年冷流場的研究結果應用於，受“太極型”鈍體及膛線化噴嘴所調制的燃燒爐中，探討流場控制技術對燃燒特性的影響。藉由拍照攝影、Schlieren 光學技術、熱電偶溫度量測、及燃燒氣體濃度分析等實驗方法，研究非預混的燃燒爐受旋渦所調制時的火焰行為、火焰長度、溫度分佈、燃燒特性、熱釋放率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引響。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。以熱電偶探針進行溫度的量測，得到燃燒場的溫度分佈，並計算熱釋放率，用以判斷流場模態對燃燒的效應。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。第三年中，以聲波激擾之主動式流動控制方式，調制受“太極型”鈍體及膛線化噴嘴的燃燒能力，在不同燃料及空氣雙旋流調制速度操作條件下，達到旋渦尾流性質的可調性，並回饋與彙整前二年所得到的結果。過程中將以函數產生器及功率放大器，所產生的不同波形、頻率及振幅為驅動訊號。於中心燃料噴流的噴嘴上游架設可調動式的聲波源的頻率及振幅，藉由驅動訊號的帶動，產生不同噴流的擾動性質，包含頻率、壓力波與紊流強度等特性。實驗量測以熱電偶溫度量測擷取燃燒場的溫度分佈，並計算熱釋放率；並輔以拍照攝影觀察火焰形狀，及以高溫型熱線風速儀偵測火焰的非穩態結構，清楚界定雙旋流調制燃燒時受聲波激擾時的物理特性與氣動力之關係。可以預期的，聲波激擾所造成的效果與其燃燒流場特性，將可回饋至前二年受“太極型＂鈍體控制的機構。以便進一步改善 “太極型＂鈍體機構與膛線噴嘴的調制能力，將設計方法與規範作有系統相關性的統整與討論。" "This project proposes a series of systematical experiments to promote the combustion efficiency by exploring the flow control mechanism on the modulation of swirling flow. The active and passive control mechanism includes the bluff-body flame stabilizer and acoustic excitation schemes. The previous study and experiments on the cold flow patterns and combustion efficiency in the non-premixed combustors shows that the mixing ratio between the fuel and air determines the combustion ability and compositions of burned gas. Therefore, the mixing of fuel and air can be increased and accelerated by using various generation mechanisms of swirling flow. This project combines the bluff-body flame stabilizer and rifled nozzle and install this new design at the outlet of a convectional combustor. This new design can increase the combustion efficiency rapidly and economically. Moreover, it can reduce the production of hydrocarbon pollution and increase the energy saving efficiency. This project is separated into three parts and finished in three years. In the first year program, A Tai-Chi type bluff-body disc will be installed at outlet of the central fuel jet and a rifled nozzle will be placed at the outlet of a convectional combustor. A dual non-premixed swirling flow will be form by combining the swirled central fuel jet and the swirled annular air jet. The authors will conduct a series of experiments of cold flow by using this dual swirling flow in the first-year program. Furthermore, the applicants will design and manufacture an apparatus to adjust the relative height between the Tai-Chi type disc and the outlet of rifled nozzle. The flow structures behind the Tai-Chi type disc will be changed by tuning the relative height. To visualize the flow structures, the streakline flow field visualization, Particle Image Velicimetry (PIV), topological analysis, hot-wire velicimeter and concentration-tracing schemes will be applied to find the optimal configuration of Tai-Chi type disc and operation conditions. Moreover, the flow patterns, velocity contours, turbulent properties, the average and instantaneous responses, unstable flows and the mixing efficiency will bee also explored. Additionally, the carbon dioxide (CO2) concentration detector will be utilized to detect the distribution of CO2. The distribution of CO2 can be employed to determine the mixing efficiency. The data of mixing efficiency will be feedbacked to the adjustor of Tai-Chi type disc to modulate the wake property. Finally, these experimental results in the first-year program will be applied to the second-year program for directing the dual swirled flow in a combustor. 表C011 共4頁第 4頁 In the second year program, the experimental results of cold-flow field induced from the dual-swirling flow will be conducted in a combustor to explore the flame configurations and the combustion efficiency. The direct-photo scheme, Schlieren optical system, thermo-couple detector, and the concentration analyzer will be utilized to modulate the flame behaviors, flame height, temperature distribution, combustion properties, heat release rate and concentration distribution. The flame configuration can be used to determine the effect of air/fuel ratio on the flame behaviors. The Schlieren optical system can detect the density distribution near the nozzle outlet to obtain the first differential images. Furthermore, the density distribution can be applied to visualize the coherent structures of wake vortices behind the nozzles. The temperature distribution will be measured by using a thermal couple. Furthermore, the heat release rate and the flow patterns can be determined by using the temperature distribution. Additionally, the gas-concentration analyzer will be utilized to detect the components of combusted gas and to determine the combustion rate for improving the combustion efficiency. In the third year program, the applicants will use an acoustic excitation to adjust the flow patterns behind the Tai-Chi type bluff-body disc actively. The adjustability of wake vortex will be controlled by the active acoustic excitation and the dual-swirling flow. In the period, a function generator and power amplifier will be used to generate by changing the waveform, frequency, and amplitude to drive a speaker. A frequency-and-amplitude tunable acoustic source will be installed in front of the nozzle of central fuel jet. The various turbulent properties of central fuel jet will be generated in different form of frequency, pressured wave, turbulent intensity, etc. Moreover, the temperature distribution of flame field will be measured by using the thermal couple. Therefore, the heat release rate can be determined by using the temperature distribution. In addition, the flame structures will be visualized by using the direct-photography. However, the unstable flame structures will be calibrated by using a high-temperature type velocimeter. Finally, the aerodynamic properties of the dual swirling flow caused from the acoustic excitation will be clarified. Moreover, the flame height can be adjusted, the heat release rate can be increased and the hydrocarbon pollution can be lowered by combining the effects of acoustic excitation and the dual-swirling flow. Consequently, a more efficient combustor will be designed."

Keyword(s)

流動控制
冷流場
燃燒效率
聲波激擾
Flow Control
Cold Flow
Combustion efficiency
Acoustic Excitation

DSpace CRIS

A Design and Analysis of Novel Non-Premixed Dual-Swirling Combustion Nozzle

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