發(fā)布時間：2018-10-16 13:43

【摘要】：密閉空間內層流預混火焰?zhèn)鞑ナ强扇細怏w安全、內燃機應用和爆轟波理論等領域重要的燃燒科學與技術課題。如何有效地預防可燃氣體的火災爆炸(爆轟)事故,控制其發(fā)展蔓延和減輕事故危害,這些問題的解答需要科學研究作為依據。而內燃機領域也亟需基礎的火焰?zhèn)鞑祿驮敿毜幕瘜W反應機理來建立燃燒模型,以實現(xiàn)其自身結構的優(yōu)化改進和對替代燃料的性能評估。因此,為了更加全面地揭示火焰發(fā)生、發(fā)展以及加速突變的本質規(guī)律和機理,深入剖析火焰內部反應區(qū)結構和物理化學過程,并建立綜合完善的化學動力學模型,同時也為了積累更多有用的火焰?zhèn)鞑セA數據,本文利用實驗、理論和數值模擬手段對密閉空間內典型可燃氣體層流預混火焰?zhèn)鞑ソY構形態(tài)、火焰加速和突變動力學、層流火焰速度以及化學反應機理開展了細致嚴謹的科學研究。 本文首先對氫-空氣和丙烷-空氣預混火焰在封閉管道內的傳播特性開展研究,內容包括火焰和超壓動力學、火焰與誘導流場和壓力波的相互作用等。高速紋影攝像技術用于捕捉和記錄火焰位置和形態(tài)變化,高精度壓力傳感器用于探測管道內瞬時的壓力變化特性。實驗結果表明,封閉管道內預混火焰?zhèn)鞑ソ洑v了復雜的形狀變化,呈現(xiàn)出經典的或變形的Tulip結構,由于受到火焰加速和減速、壁面約束、邊界層效應、壓力波效應以及火焰誘導流場等影響,火焰裙邊運動、火焰與壁面接觸點運動、Tulip尖端運動和火焰尖端運動等都表現(xiàn)出明顯的階段性特征,Bychkov模型對基本運動參數(位置和速度)的預測并不理想,僅適用于火焰發(fā)展早期。所有工況都觀察到了火焰尖端位置(速度)及壓力脈動現(xiàn)象,只是頻率和幅度各有不同。變形Tulip結構并不是封閉管道內氫-空氣預混火焰特有的行為,在化學計量比(中=1)附近的預混丙烷-空氣火焰中也有發(fā)現(xiàn),且Tulip變形過程中都伴隨著顯著的火焰尖端速度脈動。壓力波并不是火焰速度脈動及Tulip變形的誘因,但確實會起到促進作用；而壁面和邊界效應,楔形擠壓流、水力學不穩(wěn)定性及火焰誘導流動的綜合效應可能是主要物理起因。 隨后我們利用圓柱形雙燃燒室實驗臺,結合高速攝像和紋影技術,對C2碳氫燃料(主要是乙烷、乙烯和乙炔等)常壓和高壓層流火焰速度開展了實驗研究和測量,并分析了當量比、初始壓力和燃料分子結構對火焰?zhèn)鞑サ挠绊憽３簩嶒灲Y果與權威文獻數據吻合得很好,并對一些歷史數據較少且分散的工況做了補充和驗證。對于不同燃料反應體系,二氧化碳稀釋的作用機制明顯不同。表觀的,二氧化碳會抑制乙烯火焰以及富燃料乙烷火焰?zhèn)鞑?但對于乙炔火焰以及貧燃料乙烷火焰幾乎沒有影響,表明其抑制作用被抵消�？傮w來說,USC Mech Ⅱ對層流火焰速度的定量預測不是很理想(特別是對高壓火焰),僅能較好地反映火焰速度的變化趨勢。 本文討論分析了USC MechⅡ模型存在的問題和缺陷,進而以化學動力學領域最新的研究成果為基礎,借助量子化學計算和實驗測量等手段,建立了新的綜合化學反應模型。實驗驗證表明新模型對常壓和高壓典型可燃氣體層流預混火焰速度的預測能力相比USC Mech Ⅱ有了顯著的提高。新模型為我們揭示了乙烷、乙烯、乙炔火焰體系的主要反應路徑；發(fā)現(xiàn)了碳氫燃料火焰結構和燃燒行為之間很多相似之處；同時還指出了高壓火焰體系中一些重要的基元反應以及火焰速度對反應速率常數的敏感度變化(相比常壓情況)。二氧化碳稀釋對火焰體系的化學和第三體效應,主要表現(xiàn)為抑制和促進兩個矛盾方面。一方面,過量的C02會逆轉反應CO+OH=CO2+H,并增強第三體反應H+O2(+M)=HO2導致體系H原子濃度降低；另一方面,作為強第三體,C02稀釋同樣也會加劇HCO的分解反應HCO (+M)=H+CO (+M),從而補償一定的H原子損失。表觀的二氧化碳稀釋效果是這兩種內在作用機制相互競爭和抵消的綜合體現(xiàn)。乙炔火焰中由于反應CO+OH=CO2+H并不是產物C02主要生成通道,因而其重要性減弱,二氧化碳稀釋的抑制和促進作用相互抵消；而乙烯和乙烷火焰速度對HCO分解反應速率常數的敏感度較低(反應重要性較弱,尤其是在高壓下),因此火焰總體受到抑制。特別的,二氧化碳稀釋對富燃料乙烷火焰體系的化學和第三體效應較弱,體系的熱量和質量輸運性質以及混合物組成和密度的變化是導致火焰減速的本質原因。與乙烷和乙烯火焰不同的是,0原子(而不是H原子)在乙炔火焰體系中起著決定性作用,其濃度變化將直接影響火焰?zhèn)鞑バ袨椤?br/>[Abstract]:Laminar premixed flame propagation in confined space is an important topic of combustion science and technology in the fields of combustible gas safety, internal combustion engine application and detonation wave theory. How to effectively prevent the fire explosion (detonation) accident of combustible gas, control its development spread and alleviate the accident hazard, the answer of these questions need scientific research as the basis. In the field of internal combustion engine, it is necessary to establish combustion model based on flame propagation data and detailed chemical reaction mechanism, so as to realize optimization improvement of its own structure and performance evaluation of alternative fuel. Therefore, in order to reveal the essence rule and mechanism of flame generation, development and accelerating mutation more comprehensively, deeply analyze the structure and physical and chemical process of flame interior reaction zone, and establish a comprehensive and perfect chemical kinetic model. At the same time, in order to accumulate more useful flame propagation basic data, this paper uses experiment, theory and numerical simulation to simulate the structure, flame acceleration and mutation dynamics of typical combustible gas laminar premixed flame in confined space. The laminar flame velocity and chemical reaction mechanism have carried out detailed and rigorous scientific research. Firstly, the propagation characteristics of hydrogen-air and propane-air pre-mixed flame in closed pipelines are studied. The contents include flame and overpressure dynamics, flame and induced flow field and pressure wave. The high-precision pressure sensor is used to detect the instantaneous pressure change in the pipeline, and the high-precision pressure sensor is used for capturing and recording flame position and shape change. The experimental results show that the pre-mixing flame propagation in the closed pipeline has undergone a complex shape change, which presents a classical or deformed Tulp structure, which is affected by flame acceleration and deceleration, wall restraint, boundary layer effect, pressure wave effect and flame-induced flow field, etc. The motion, flame and wall contact movement, Tulp tip movement and flame tip movement all show obvious periodic characteristics. The prediction of basic motion parameters (position and velocity) by Bychbach model is not ideal, and it is only suitable for flame development. Earlier, the flame tip position (velocity) and pressure pulsation phenomenon were observed for all operating conditions, except for frequency and amplitude. The deformation of the Tulp structure is not characteristic of the hydrogen-air pre-mixing flame in the closed pipeline, and is also found in the pre-mixed propane-air flame near the stoichiometric ratio (= 1), and there is a significant flame tip speed during the Tulp deformation process. Pulsation. Pressure wave is not the cause of flame velocity fluctuation and Tulp deformation, but does play a promoting role; and the wall surface and boundary effect, wedge-shaped extrusion flow, hydraulic instability and flame-induced flow can be the main physics. Then we carried out experimental research and measurement on C2 hydrocarbon fuel (mainly ethane, ethylene and acetylene, etc.) at normal pressure and high pressure laminar flame speed by using cylindrical double combustion chamber experiment table, combined with high speed camera and image shadow technology. The equivalence ratio, the initial pressure and the molecular structure of the fuel are analyzed. The experimental results of atmospheric pressure are well coincident with authoritative literature data, and some historical data are less and dispersed. Replenishment and verification. For different fuel reaction systems, carbon dioxide dilution works Visible, carbon dioxide suppresses the flame propagation of ethylene and fuel-rich ethane, but has little effect on acetylene flame and lean-fuel ethane flame, indicating its suppression The effect is cancelled. In general, the quantitative prediction of laminar flame velocity by USC Mech II is not ideal (especially for high-pressure flame) and only better reflects flame speed. In this paper, the problems and defects of USC Mech 鈪，

本文編號：2274543