Effect of equivalence ratio and temperature on soot formation in partially premixed counterflow flames
Effect of equivalence ratio and temperature on soot formation in partially premixed counterflow flames
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DOI：
10.1016/j.combustflame.2022.112088
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发表时间：
2022-08
影响因子：
4.4
通讯作者：
Kevin Gleason;F. Carbone;A. Gomez
中科院分区：
文献类型：
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作者：
Kevin Gleason;F. Carbone;A. Gomez
在当量比Φ = 6.5，5.0和4.0，最高温度约为200 K的乙烯部分预混逆流火焰中，对碳烟的形成进行了详细的量化（体积分数、颗粒尺寸、数浓度和光发射率色散指数）。重点是研究峰值温度和当量比对碳烟形成的影响，同时保持恒定的整体应变和化学计量混合物分数。氧气逐渐从氧化剂转移到扩散火焰的燃料流中，以稳定Φ减小的部分预混火焰，显示出由稳定在滞止平面的燃料侧的富预混火焰分量和稳定在氧化剂侧的扩散火焰分量组成的双火焰结构。在夹在两个火焰分量之间的区域中检测到烟灰，烟灰形成于两个火焰分量中，并且在颗粒停滞平面（PSP）处径向对流离开。在固定的Φ下，提高峰值温度总是提高整个探测区域的碳烟体积分数。反之亦然，在固定的峰值温度下，降低当量比会导致预混火焰分量从扩散火焰分量移开，随之而来的是碳烟形成区域的加宽以及碳烟体积分数和碳烟颗粒尺寸通过增强表面生长而增加。在PSP附近的区域的详细探测提供了从分子氧的烟灰氧化的证据。此外，当最高温度足够低时，由于表面氧化抑制了表面生长，净烟灰产生速率变为负值。比较sootnumberproduction率推断从实验中的二聚率的苯（C6H6），萘（C10H8），芘（C16H10）表明，只有最小的芳香族化合物存在于火焰中，在足够大的浓度，以占烟灰成核。这一观察结果适用于扩散火焰和预混火焰的组成部分，并证实了以前的研究结果，在严格的扩散火焰。
Soot formation is quantified in detail (volume fraction, particle size, number concentration, and light emissivity dispersion exponent) in a series of partially premixed counterflow flames of ethylene at equivalence ratios, Φ, equal to 6.5, 5.0, and 4.0, and with maximum temperature spanning approximately 200 K. The focus is to investigate the effect of peak temperature and equivalence ratio on soot formation while maintaining constant global strain and stoichiometric mixture fraction. Oxygen is progressively displaced from the oxidizer to the fuel stream of a diffusion flame to stabilize partially premixed flames of decreasing Φ, showing a double-flame structure consisting of a rich premixed flame component stabilized on the fuel side of the stagnation plane and a diffusion flame component stabilized on the oxidizer side. Soot is detected in the region sandwiched between the two flame components, is formed in both of them, and is convected away radially at the Particle Stagnation Plane (PSP). At fixed Φ, raising the peak temperature invariably raises the soot volume fraction throughout the probed region. Vice versa, at fixed peak temperature, lowering the equivalence ratio causes the premixed flame component to shift away from the diffusion flame component, with the consequent broadening of the soot forming region and an increase in both soot volume fraction as well as soot particle sizes through an enhancement of surface growth. Detailed probing of the region in the vicinity of the PSP offers evidence of soot oxidation from molecular oxygen. Furthermore, when the maximum temperature is sufficiently low, the net soot production rate turns negative because surface oxidation overwhelms surface growth. Comparing the sootnumberproduction rate inferred from experiments to the dimerization rate of benzene (C6H6), naphthalene (C10H8), and pyrene (C16H10) reveals that only the smallest aromatics are present in flames at sufficiently large concentrations to account for soot nucleation. This observation applies to both the diffusion flame and the premixed flame components and confirms previous findings in strictly diffusion flames.