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Heat release and flame structure measurements of self-excited acoustically-driven premixed methane flames

机译:自激声驱动的预混合甲烷火焰的放热和火焰结构测量

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An open-open organ pipe burner (Rijke tube) with a bluff-body ring was used to create a self-excited, acoustically-driven, premixed methane-air conical flame, with equivalence ratios ranging from 0.85 to 1.05. The feed tube velocities corresponded to Re = 1780-4450. Coupled oscillations in pressure, velocity, and heat release from the flame are naturally encouraged at resonant frequencies in the Rijke tube com-bustor. This coupling creates sustainable self-exited oscillations in flame front area and shape. The period of the oscillations occur at the resonant frequency of the combustion chamber when the flame is placed ~1/4 of the distance from the bottom of the tube. In this investigation, the shape of these acoustically-driven flames is measured by employing both OH planar laser-induced fluorescence (PLIF) and chemilumi-nescence imaging and the images are correlated to simultaneously measured pressure in the combustor. Past research on acoustically perturbed flames has focused on qualitative flame area and heat release relationships under imposed velocity perturbations at imposed frequencies. This study reports quantitative empirical fits with respect to pressure or phase angle in a self-generated pressure oscillation. The OH-PLIF images were single temporal shots and the chemiluminescence images were phase averaged on chip, such that 15 exposures were used to create one image. Thus, both measurements were time resolved during the flame oscillation. Phase-resolved area and heat release variations throughout the pressure oscillation were computed. A relation between flame area and the phase angle before the pressure maximum was derived for all flames in order to quantitatively show that the Rayleigh criterion was satisfied in the combustor. Qualitative trends in oscillating flame area were found with respect to feed tube flow rates. A logarithmic relation was found between the RMS pressure and both the normalized average area and heat release rate for all flames.
机译:具有钝体环的开式器官风管燃烧器(Rijke管)用于产生自激,声学驱动的甲烷-空气预混合锥形火焰,当量比为0.85至1.05。进料管的速度对应于Re = 1780-4450。在Rijke管燃烧室的共振频率处自然会促进压力,速度和火焰释放热量的耦合振荡。这种耦合在火焰的前部区域和形状中产生可持续的自激振荡。当火焰放置在距燃烧管底部约1/4处的距离处时,振荡周期以燃烧室的共振频率发生。在这项研究中,通过同时使用OH平面激光诱导荧光(PLIF)和化学发光成像来测量这些声学驱动火焰的形状,并将图像与燃烧室中同时测量的压力相关联。过去对声学扰动火焰的研究集中于定性火焰面积和在施加频率下施加速度扰动下的放热关系。这项研究报告了自生压力振荡中相对于压力或相角的定量经验拟合。 OH-PLIF图像是单个时间快照,化学发光图像在芯片上进行了相位平均,因此使用15次曝光创建了一张图像。因此,两个测量在火焰振荡期间都是时间分辨的。计算了整个压力振荡过程中的相分辨面积和放热变化。为了定量显示燃烧器中的瑞利标准,得出了所有火焰的火焰面积与最大压力之前的相角之间的关系。发现了与进料管流速有关的振荡火焰区域的定性趋势。在所有火焰的RMS压力与归一化平均面积和放热率之间都发现了对数关系。

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