低温燃料化学特性对湍流预混火焰传播的影响  

Role of Low-Temperature Fuel Chemistry on Turbulent Flame Propagation

作　　者：张帆[1] 任哲 钟生辉 尧命发[1] 彭志军[1] ZHANG Fan;REN Zhe;ZHONG Shenghui;YAO Mingfa;PENG Zhijun(State Key Laboratory of Engines,Tianjin University,Tianjin 300072,P.R.China.)

机构地区：[1]天津大学内燃机燃烧学国家重点实验室,天津300072

出　　处：《物理化学学报》2019年第2期158-166,共9页Acta Physico-Chimica Sinica

基　　金：国家自然科学基金青年基金(51506146)和重大研究计划重点项目(91541205)资助~~

摘　　要：大分子碳氢燃料的低温化学反应及两阶段点火特性会显著影响火焰的分区及燃烧情况。本文采用数值模拟的方法探究了正庚烷/空气预混混合气在RATS燃具上的湍流火焰传播,与试验结果具有一致性。模拟使用的是44种物质,112步的正庚烷简化动力学机理。使用Open FOAM的reacting Foam求解器建立了简化模拟流道及出口的三维模型,模拟了在大气环境下,初始反应温度450–700 K、入口速度6 m·s^(-1)与10 m·s^(-1)、焰前流动滞留时间100 ms及60 ms、当量比φ=0.6的正庚烷/空气混合气湍流火焰燃烧情况。结果发现,标准化湍流燃烧速度与混合气初始温度以及流动滞留时间有关。在低温点火阶段,正庚烷氧化程度受到初始温度与速度的影响,燃料分解并在预热区中产生大量中间物质如CH_2O,继而会影响湍流火焰燃烧速度。随着初始反应温度的升高,湍流燃烧火焰逐渐由化学反应冻结区过渡到低温点火区;温度超过一定数值后,燃料不再发生低温反应,此时燃烧位于高温点火区域。In modern advanced internal combustion engines such as homogeneous compression ignition engine(HCCI)and reactivity controlled compression ignition engine(RCCI),turbulence/chemistry interactions have a dramatic influence on the combustion efficiency.In particular,the low-temperature fuel chemistry and two-stage ignition of large hydrocarbon fuels can significantly affect the turbulent flame regimes and propagation.The turbulent flame propagation and flame structure of a turbulent premixed n-heptane/air flame is simulated in a slot,i.e.,reactor-assisted turbulent slot(RATS)burner.In the center,a premixed n-heptane/air gas mixture flows out from the burner,exiting into the surrounding atmosphere.In order to maintain a high Reynolds number for the flame,a pilot flame consisting of stoichiometric methane/air is applied.The GRI3.0 mechanism for methane/air mixture is adopted.A three-dimensional(3D)numerical simulation model is established based on OpenFOAM reactingFoam solver.A reduced kinetic mechanism of n-heptane consisting of 44 species and 112 reactions is employed,which is validated against the detailed mechanism with regard to the ignition delay time over a wide range of the initial temperature,equivalence ratio,and pressure.Then,the effects of the reactant temperature(ranging from 450 to 700 K),inlet velocity(6 m·s?1 and 10 m·s?1),and pre-flame flow residence time(100 ms and 60 ms)on the turbulent flame combustion of the n-heptane/air mixture with an equivalent ratio of 0.6,are investigated by performing 3D simulations.Twelve cases are considered and analyzed based on the flow residence time and ignition delay time.The 2D span-wise temperature contour is used to show that when the ignition Da number and fuel reactivity increase,the flame temperature increases and the flame height decreases,indicating a stronger turbulent burning velocity(ST).The results coincide well with experiment results and indicate that the extent of fuel oxidation is affected by the reactant temperature and inlet velocity during the low

关 键 词：低温燃料化学特性 两阶段点火 正庚烷 火焰分区 

分 类 号：O643[理学—物理化学]