Distributed Lean Direct Injection (DLDI) combustor is a new promising low NOx emission combustor. The ignition process independently occurs in the pilot stage chamber, which partly confines the swirled spray at the small confinement ratio. This study investigates ignition characteristics of the partly confined swirled spray experimentally, where effects of confinement length on flame propagation path and ignition probability are mainly considered. Particle image velocimetry, Mie scattering, phase Doppler anemometry and high-speed visualization were used to reveal the mechanisms of flame propagation and stabilization. The ignition probability was firstly counted in three chambers with the length varying from 18 mm to 27 mm, when pressure drop, ΔP, was 3000 Pa, and total equivalence ratio, ${\varphi }_{overall}$, varied from 0.67 to 0.73. Results show that reduction of the chamber length increases the ignition probability. To interpret this trend, aerodynamics, droplets characteristics and ignition process in three chambers were analyzed at $\mathrm{\Delta }P=3000$ Pa and ${\varphi }_{overall}=0.73$. The time-average flow field shows that the modification of chamber length results in changes of the confinement length of the central toroidal recirculation zone (CTRZ). Furthermore, the structure of CTRZ is directly impacted by changes of the confinement length. The reduction of the confinement length makes more air flow back, which means the greater recirculation capability of the CTRZ. More recirculating air can transport more droplets back into the CTRZ before sparking, which can also transport more high-temperature mixture there to help hold flame during ignition process. The high-speed visualization shows that the failed mode of ignition process is that the swirling flame can grow up at the beginning of Phase 3, but will blow out gradually after the extinction of the flame in corner recirculation zone (CRZ). According to characteristics of aerodynamics, droplets characteristics and ignition process, it can be concluded that since significant time is taken for flame to reach the fully burning state, the reduction of the confinement length improves the recirculation capability of the CTRZ which helps the partly confined flame get better stability. In addition, in Phase 2 of ignition process, greater recirculation capability makes the anchored position of the edge flame more upstream, which can make the propagation path shorter.

分布式稀薄直接喷射（DLDI）燃烧器是一种新兴的低NOx排放燃烧器。点火过程独立地发生在先导级腔室中，这部分将涡旋状喷雾部分限制在较小的限制比下。本文研究了部分受限旋流喷雾的着火特性，主要考虑了限制长度对火焰传播路径和着火概率的影响。粒子图像测速，米氏散射，相位多普勒风速和高速可视化被用来揭示火焰传播和稳定的机制。当压力降ΔP为3000 Pa，总当量比为3时，首先在长度为18 mm至27 mm的三个腔室中计算点火概率。${\varphi }_{ØvË\mathrm{[R}\mathrm{一种}升升}$，从0.67到0.73不等。结果表明，减小燃烧室长度会增加点火概率。为了解释这种趋势，在三个腔室中分析了空气动力学，液滴特性和点火过程$\mathrm{\Delta }P=3000$ 帕和 ${\varphi }_{ØvË\mathrm{[R}\mathrm{一种}升升}=0.73$。时间平均流场表明，腔室长度的改变导致中央环形再循环区（CTRZ）的限制长度发生变化。此外，CTRZ的结构直接受围长变化的影响。限制长度的减小使更多的空气回流，这意味着CTRZ具有更大的再循环能力。更多的再循环空气可以在产生火花之前将更多的液滴传送回CTRZ，这也可以在其中传送更多的高温混合物，从而在点火过程中帮助保持火焰。高速可视化显示，点火过程的失败模式是在第3阶段开始时漩涡状火焰会长大，但会在角落再循环区（CRZ）熄灭后逐渐吹灭。根据空气动力学特性，飞沫特性和着火过程，可以得出结论，由于花费大量时间使火焰达到完全燃烧状态，限制长度的减小提高了CTRZ的再循环能力，这有助于部分限制火焰获得更好的稳定性。此外，在点火过程的第2阶段，更大的再循环能力使边缘火焰的锚定位置更靠上游，这会使传播路径更短。