二甲醚湍流射流推举火焰的燃烧机理研究

对长、宽、高为650 mm×400 mm×12 mm的半闭口狭窄矩形通道（海伦-肖装置）内的甲烷/空气层流预混火焰传播过程进行了实验研究，探究当量比φ在0.6~1.2范围内、火焰传播角度ω在垂直向下-90°至垂直向上90°区间对火焰前锋轮廓发展及非标准层流火焰速度的影响。结果表明：火焰在通道内的传播分为热膨胀、准稳态传播和端壁效应3个阶段，每个阶段具有各自不同的前锋轮廓特征。由于瑞利-泰勒不稳定性机制的作用，所有当量比工况下向上传播的火焰均在准稳态传播阶段中呈现出明显的锋面褶皱与胞状结构；对向下传播的火焰而言，其在贫燃工况（φ为0.6，0.8）下的胞状不稳定性得到了有效抑制，而在当量比φ=1.0及富燃工况（φ=1.2）下，该稳定性效应并不显著。火焰瞬时速度与标准层流速度的比值Ui/UL，在φ=0.6的极贫燃工况与其他当量比工况下展现出明显不同的发展特性，极贫燃工况火焰向上传播时（ω=90°），Ui/UL随着传播过程的进行一直增大，直到火焰触碰壁面末端熄灭，整个过程Ui/UL与火焰传播方向呈正相关关系；而对于其他当量比工况，Ui/UL在传播过程中均先升高后下降，火焰触碰壁面末端熄灭前其值趋于稳定，其平均速度与标准层流速度的比值Ua/UL在水平传播（ω=0°）时达到最大值。

Study on Combustion Mechanism of Dimethyl Ether Turbulent Lifted Jet Flames

The direct numerical simulation(DNS) was conducted to analyze flame structure, combustion modes and lift off stabilization mechanism of the dimethyl ether (DME) turbulent lifted jet flame. The fuel was ejected from the slot with an initial temperature of 500 K and the jet velocity of 138 m/s; the initial temperature of the coflow air was 1 000 K, the flow velocity was 3 m/s, and the initial pressure was 0.506 6 MPa. The results show that the DME lifted jet flame structure is rather different from the traditional edge flame, i.e. there exists a low temperature heat production branch as well as a following intermediate temperature ignition branch in the jet core zone, and additionally, the stabilization point is located at the fuel lean side; four combustion modes including cool flame zone (CFZ), intermediate temperature zone (ITZ), high temperature rich burn zone (HTR) and high temperature lean burn zone (HTL) modes coexist in the turbulent lifted reacting zone; turbulent mixing is dominated in the CFZ and ITZ zones, and it will inhibit the local low temperature heat production rate; in HTR and HTL zones, heat release reaction overwhelms turbulent mixing, but turbulence can considerably enhance heat production in the ultra lean and high temperature zone; the majority heat is produced in the HTL and HTR zones, while contributions of CFZ and ITZ to the total heat production are fairly ignorable, however, the medium and low temperature species generated in CFZ and ITZ play an important role in accelerating the high temperature mixture ignition; stabilization of the current lift off DME jet flame is governed by the fuel lean and high temperature auto ignition mechanism.