DNS of a turbulent lifted DME jet flame
DNS of a turbulent lifted DME jet flame
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DOI：
10.1016/j.combustflame.2016.04.007
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发表时间：
2016-07
影响因子：
4.4
通讯作者：
Y. Minamoto;Jacqueline H. Chen
中科院分区：
文献类型：
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作者：
Y. Minamoto;Jacqueline H. Chen
采用三维直接数值模拟（DNS）方法研究了升力二甲醚（DME）狭缝射流火焰在高压下的低温放热（LTHR）化学反应、负温度系数（NTC）化学反应和射流在加热共流中剪切产生的湍流之间的相互作用。通过调节混合物分数、局部反应区域和局部热释放率，湍流火焰显示出“五臂”结构，这是在层流二甲醚提升火焰中观察到的[Krisman等人，（2015）]。研究了稳定点和三相点的传播特性。潜在稳定点，即以最佳温度和混合分数条件为特征的空间位置，表现出反应速率大、分子扩散可忽略的自燃特性。实际稳定点与各展向位置的稳定点池中最上游的样本重合，显示出大扩散的被动火焰结构。沿着三点附近的化学计量表面的传播速度与理论得到的渐近值进行比较[Ruetsch et al.,(1995)]。在化学计量条件下，火焰位移速度的渐近和平均DNS值偏差为1.7倍。然而，考虑到低温物种对局部火焰速度增加的影响，这两个值变得具有可比性。这表明，当第一级低温点火产生的大量低温产物被高速射流输送到升力火焰时，二级点火通过提高层流火焰速度来影响三相点传播速度。
A three-dimensional direct numerical simulation (DNS) of a turbulent lifted dimethyl ether (DME) slot jet flame was performed at elevated pressure to study interactions between chemical reactions with low-temperature heat release (LTHR), negative temperature coefficient (NTC) reactions and shear generated turbulence in a jet in a heated coflow. By conditioning on mixture fraction, local reaction zones and local heat release rate, the turbulent flame is revealed to exhibit a “pentabrachial” structure that was observed for a laminar DME lifted flame [Krisman et al., (2015)]. The propagation characteristics of the stabilization and triple points are also investigated. Potential stabilization points, spatial locations characterized by preferred temperature and mixture fraction conditions, exhibit autoignition characteristics with large reaction rate and negligible molecular diffusion. The actual stabilization point which coincides with the most upstream samples from the pool of potential stabilization points fovr each spanwise location shows passive flame structure with large diffusion. The propagation speed along the stoichiometric surface near the triple point is compared with the asymptotic value obtained from theory [Ruetsch et al., (1995)]. At stoichiometric conditions, the asymptotic and averaged DNS values of flame displacement speed deviate by a factor of 1.7. However, accounting for the effect of low-temperature species on the local flame speed increase, these two values become comparable. This suggests that the two-stage ignition influences the triple point propagation speed through enhancement of the laminar flame speed in a configuration where abundant low-temperature products from the first stage, low-temperature ignition are transported to the lifted flame by the high-velocity jet.