On the ignition kernel formation and propagation: an experimental and modeling approach
On the ignition kernel formation and propagation: an experimental and modeling approach
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DOI：
10.1088/1361-6463/acc411
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发表时间：
2023-03
期刊：
影响因子：
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通讯作者：
James Shaffer;Steven Luna;Weiye Wang;F. Egolfopoulos;Omid Askari
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文献类型：
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作者：
James Shaffer;Steven Luna;Weiye Wang;F. Egolfopoulos;Omid Askari
下一代先进燃烧装置正在开发中，可在超高压条件下运行。然而，在这种极端条件下，火焰往往变得不稳定，并且诸如层流火焰速度的基本特性的测量变得具有挑战性。解决这个问题的一个潜在方法是在球形膨胀火焰实验中测量点火影响区域。由于高拉伸率（即小半径），该区域中的火焰更能抵抗扰动并保持平滑。稳定的火焰传播允许改进的火焰测量，然而，实验观察到的核传播是炎症和点火等离子体的函数。因此，本研究的目标是更好地了解点火过程中等离子体的形成和传播，这将允许可靠的层流火焰速度测量。为了实现这一目标，在高压下工作的热等离子体的研究，重点是火花能量的点火核心的形成的影响。利用高速纹影成像系统对等离子体的热效应进行了实验观察。使用电压和电流探头测量等离子体鞘层电压降作为数值建模的输入，测量等离子体内耗散的能量。测量的内核传播速率用于评估模型的准确性。实验和建模进行在干燥的空气中，在1，3，和5个大气压，以及在CH 4-N2的混合物在1个大气压，和内核半径，温度和质量的报告。辉光等离子体的压降（作为非热损失）测量值约为330 ± 5 V（1 atm下的干燥空气），与压力、气体成分、电极表面质量、电极几何形状、电极形状和电流密度有很大的依赖性。电弧等离子体内的相同损耗被测量为15 ± 5 V，然而与电弧传播一致的电弧相位损耗显著更高（1.45 V），这表明在电弧相位期间发生了额外的未考虑的现象。利用这些损失，示出了建模结果，以预测在所观察到的核尺寸的10%-20%内的最终核半径。建模和实验结果之间的差异被确定为假设的主要损失机制（跨鞘层形成的电压降）保持恒定的辉光放电的持续时间的结果。电弧放电的差异与几个潜在的来源进行了讨论，但是，需要更多的研究，以更好地了解电弧的形成如何影响内核的传播。
The next generation of advanced combustion devices is being developed to operate under ultra-high-pressure conditions. However, under such extreme conditions, flame tends to become unstable and measurement of fundamental properties such as the laminar flame speed becomes challenging. One potential method to resolve this issue is measuring the ignition-affected region during spherically expanding flame experiments. The flame in this region is more resistant to perturbations and remains smooth due to the high stretch rates (i.e. small radii). Stable flame propagation allows for improved flame measurement, however, the experimentally observed kernel propagation is a function of both inflammation and ignition plasma. Therefore, the goal of the present study is to better understand the plasma formation and propagation during the ignition process, which would allow for reliable laminar flame speed measurements. To accomplish this goal, thermal plasma operating at high pressures is studied with emphasis on the spark energy effects on the formation of the ignition kernel. The thermal effect of the plasma is experimentally observed using a high-speed Schlieren imaging system. The energy dissipated within the plasma is measured with the use of voltage and current probes with a measurement of plasma sheath voltage drop as an input to numerical modeling. The measured kernel propagation rate is used to assess the accuracy of the model. The experiments and modeling are conducted in dry air at 1, 3, and 5 atm as well as in CH4-N2 mixtures at 1 atm, and kernel radius, temperature, and mass are reported. The voltage-drop (as a non-thermal loss) is measured to be approximately 330 ± 5 V (dry air at 1 atm) for glow plasma with a large dependency on pressure, gas composition, electrode surface quality, electrode geometry, electrode shape, and current density. The same loss within the arc plasma is measured to be 15 ± 5 V, however the arc phase loss which agrees with arc propagation is significantly higher (∼45 V) which suggest additional unaccounted for phenomena occurring during the arc phase. With these losses, the modeling results are shown to predict the final kernel radius within 10%–20% of the observed kernel size. The difference found between the modeling and experimental results is determined to be a result of assuming that the primary loss mechanism (voltage drop across sheath formation) remains constant for the duration of glow discharge. The discrepancy for arc discharge is discussed with several potential sources, however, additional studies are required to better understand how the arc formation affects the kernel propagation.