Influence of spark ignition in the determination of Markstein lengths using spherically expanding flames
Influence of spark ignition in the determination of Markstein lengths using spherically expanding flames
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DOI：
10.1016/j.fuel.2016.08.013
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发表时间：
2016-12
期刊：
影响因子：
7.4
通讯作者：
M. Lawes;G. Sharpe;N. Tripathi;R. Cracknell
中科院分区：
文献类型：
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作者：
M. Lawes;G. Sharpe;N. Tripathi;R. Cracknell
在球形炸弹中进行了恒压向外传播火焰实验，以考察火花点火效应的持续时间和半径。这是因为在使用火花点火膨胀火焰技术测量层流燃烧速度和马克斯坦长度时，需要适当地考虑这些影响。通过改变点火能量，研究了点火能量对甲烷-空气和异辛烷-空气混合气中火焰传播的影响。事实证明，混合物的Markstein长度在火焰传播的点火能量依赖性中至关重要。对于相对较高的值，可以通过不同点火能量曲线的快速收敛来识别自持火焰速度随半径的潜在共同变化。随着Markstein长度的减小，低能火花点火会产生扭曲和皱折的火核。对于这样的混合物，由于拉伸的微弱影响，内核随后发展为非球形传播的火焰。在这些情况下，火花点火效应一直持续到大半径。结果表明，在发展阶段，使用较低的点火能量可以获得高于自持球形火焰的火焰速度。进一步表明，如果不考虑这种影响，使用标准拟合技术测量Markstein长度会导致很大的误差。这个问题被发现随着马克斯坦长度的减小而恶化，使得它的表观测量值变得越来越受火花产生的火核的任何扭曲的影响。
Constant pressure outwardly propagating flame experiments in a spherical bomb are performed to examine the duration and radius over which spark ignition effects persist. This is motivated by the need to properly account for such effects in the measurement of laminar burning velocity and Markstein length using the spark ignited expanding flame technique. Ignition energy was varied and its effects on flame propagation in methane-air and isooctane-air mixtures were studied. The Markstein length of the mixture proved critical in the ignition energy dependency of flame propagation. For relatively high values, an underlying common variation of self-sustaining flame speed with radius can be identified by the rapid convergence of curves for different ignition energies. As the Markstein length decreases, low energy spark ignition is found to give rise to a distorted and wrinkled flame kernel. For such mixtures, due to the weak effect of stretch, the kernel subsequently develops into a non-spherically propagating flame. In these cases the spark ignition effect persists up to large radius. It is shown that using low ignition energy leads to a flame speed, during the development phase, which is higher than that of a self-sustaining spherical flame. It is further shown that if this effect is not accounted for, measurements of Markstein length using standard fitting techniques results in a large error. This problem is found to worsen as the Markstein length decreases, such that its apparent measured value becomes increasingly influenced by any distortions of the flame kernel produced by the spark.