Combustion characteristics of a single decane/ethanol emulsion droplet and a droplet group under puffing conditions
Combustion characteristics of a single decane/ethanol emulsion droplet and a droplet group under puffing conditions
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DOI：
10.1016/j.proci.2016.06.191
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
J. Shinjo;J. Xia
中科院分区：
文献类型：
--
作者：
J. Shinjo;J. Xia
采用直接数值模拟（DNS）方法研究了一种正癸醇乳化液滴和一组液滴在喷吹条件下的燃烧特性。在喷吹前，在母滴的尾流中形成准稳态火焰。由于过热，引发乙醇子液滴的沸腾。随着气泡的快速增长，乙醇蒸汽不稳定地喷射出来，并与下游尾流火焰相互作用。局部气体混合物分数受此喷射的影响。气相温度和反应速率也表现出与一维稳态火焰不同的特征。在双燃料系统中，燃烧中的燃料/空气混合可以通过由于癸烷/空气和乙醇/空气的混合以及癸烷/乙醇的交叉混合而引起的标量耗散率（SDR）来表征。在火焰S曲线中，液滴尾流火焰和喷出的蒸汽之间的瞬态相互作用是明显的。通过混合分数- SDR空间中的预算分析进一步量化了这种相互作用。癸烷和乙醇之间的交叉SDR对主要燃料癸烷的SDR的变化率的贡献最初是负的，这对于膨化是特别的。之后，交叉SDR也可以变为正值。随着混合的继续，SDR的幅度变得更小。当在横向方向上发生抽吸时，喷射的蒸气可以扫过远离母体癸烷液滴的几个直径内的区域。如果其他乳液液滴在该影响区域中，则发生液滴间相互作用。一个多液滴的情况下，证明了这种相互作用，并意味着这种相互作用将发生在乳化燃料喷雾，并应考虑在模拟燃烧室中的多组分乳化燃料喷雾。
Combustion characteristics of an ethanol-in-decane emulsion droplet and a droplet group under puffing conditions have been investigated by direct numerical simulation (DNS). Before puffing, a quasi-steady flame is formed in the wake of the parent decane droplet. Due to superheating, boiling of ethanol sub-droplets is initiated. Following rapid growth of the vapor bubble, ethanol vapor is unsteadily ejected out and interacts with the downstream wake flame. The local gas mixture fraction is affected by this ejection. The gas-phase temperature and reaction rate also show different characteristics from those of a 1D steady flame. In the dual-fuel system, fuel/air mixing in combustion can be characterized by the scalar dissipation rates (SDRs) due to mixing of decane/air and ethanol/air and cross mixing of decane/ethanol. The transient interaction between the droplet wake flame and the ejected vapor by puffing is evident in the flame S-curves. The interaction is further quantified by the budget analysis in the mixture fraction – SDR space. The contribution of the cross SDR between decane and ethanol to the rate of change of the SDR of the primary fuel decane is initially negative, which is particular to puffing. Later the cross SDR can also become positive. As the mixing continues, the magnitude of the SDRs becomes smaller. When puffing occurs in the transverse direction, the ejected vapor may sweep a region within a few diameters away from the parent decane droplet. If other emulsion droplets are in this region of influence, inter-droplet interactions occur. A multiple-droplet case demonstrates this interaction and implies that such an interaction will occur in an emulsion fuel spray and should be considered in modeling a multi-component emulsion fuel spray in a combustor.