Group Combustion and Detailed Flame Structure of Liquid Fuel Spray Under the Infulence of Eddies

(1)由于液滴的成团行为和液滴产生的空气和燃料蒸气的混合物优先传播，喷雾火焰不可避免地具有复杂的结构。为了观察喷雾火焰的详细结构，在环形氢导焰稳定的预混喷雾火焰中，对OH和CH波段的光发射以及液滴散射的激光进行了同时监测和光谱分析。用相位多普勒风速仪（PDA）监测了火焰中液滴的直径和速度。实验证实，燃烧反应首先在簇间区域发生，火焰优先通过液滴的燃料蒸气传播，然后随着簇内液滴数密度沿流线减小，燃烧区逐渐进入簇内，最终以扩散燃烧方式燃烧致密的小簇或单个液滴。(2)在环形氢扩散先导火焰稳定的喷雾火焰中插入圆形棒，研究棒后尾流影响下喷雾火焰的详细结构。同时监测了火焰中OH和CH波段的光发射以及液滴散射的激光，并对有无棒的火焰进行了光谱分析。用激光多普勒测速仪（LDV）监测液滴速度。实验证实，插入杆促进了液滴团簇长度尺度的缩小和火焰在固体发光团簇中的传播。这一结果表明，由于杆后尾流的存在，簇的燃烧行为受到了湍流混合和气滴滑移速度的影响。

(1) A spray flame has inevitably a complicated structure due to grouping behavior of droplets and preferential flame propagation through the mixture of air and fuel vapor from droplets. In order to observe the detailed structure of spray flames, the light emissions in OH and CH bands, and the laser light scattered by droplets were monitored simultaneously and analyzed spectrally in the flame of a premixed spray stabilized by an annular hydrogen pilot flame. The diameter and velocity of droplets in the flame were also monitored using a phase Doppler anemometer (PDA). It was confirmed experimentally that the combustion reaction occurred first in the intercluster regions by the preferential flame propagation through the fuel vapor from droplets, and then, as the droplet number density of clusters decreased along the stream line, the combustion zone gradually moved into the clusters, and eventually dense small subclusters or single droplets burned in the diffusion combustion mode.(2) A circular rod was inserted in a spray flame stabilized by an annular hydrogen diffusion pilot flame to investigate the detailed structure of the spray flame under the influence of wake flow behind the rod. The light emissions in OH and CH bands, and the laser light scattered by droplets were monitored simultaneously and analyzed spectrally in the flame with and without the rod. The droplet velocity was also monitored using a laser Doppler velocimeter (LDV). It was confirmed experimentally that the inserted rod promoted the reduction of the length scale of droplet clusters and the flame propagation into the clusters with solid-body light emission. This result suggests that the combustion behavior of the clusters was influenced by the turbulent mixing and slip velocity between gas and droplets due to the wake flow behind the rod.