This study applies Flame Image Velocimetry (FIV) to show the in-flame flow field development with an emphasis on the jet-jet interaction and jet-swirl interaction phenomena in a single-cylinder small-bore optically accessible diesel engine. Two-hole nozzle injectors with three different inter-jet spacing angles of 45°, 90° and 180° are prepared to cause different levels of jet-jet interaction. The engine has a swirl ratio of 1.7, which is used to evaluate jet-swirl interaction of the selected 180° inter-jet spacing nozzle. High-speed soot luminosity imaging was performed at a high frame rate of 45 kHz for the FIV processing. For each inter-jet spacing angle, a total of 100 individual combustion cycles were recorded to address the cyclic variations. The ensemble averaged flow fields are shown to illustrate detailed flow structures while the Reynolds decomposition using spatial filtering is applied to analyse turbulence intensity. The results showed reduced bulk flow magnitude and turbulence intensity at smaller inter-jet spacing, suggesting the two opposed wall-jet heads colliding immediately after the jet impingement on the wall can cause flow suppression effects. This raised a concern on the mixing as lower inter-jet spacing creates more fuel-rich mixtures in the jet-jet interaction region. Despite lower flow magnitude, the cyclic variation was also estimated higher for narrower inter-jet spacing, which is another drawback of the significant jet-jet interaction. Regarding the jet-swirl interaction, the wall-jet head penetrating on the up-swirl side showed lower bulk flow magnitude as the counter-flow arrangement suppressed the flow, similar with the narrower interact-jet spacing results. However, the turbulence intensity was measured higher on the up-swirl side, suggesting the relatively weaker swirl flow vectors opposed to the penetrating wall-jet head could in fact enhance the mixing.

本研究应用火焰图像测速法 (FIV) 来显示火焰中流场的发展，重点是单缸小口径光学可接近柴油发动机中的射流相互作用和射流涡流相互作用现象。准备了具有 45°、90° 和 180° 三种不同射流间距角的两孔喷嘴喷射器，以引起不同程度的射流相互作用。发动机的涡流比为 1.7，用于评估所选 180° 喷气间距喷嘴的喷气-涡流相互作用。FIV 处理以 45 kHz 的高帧率进行高速烟尘亮度成像。对于每个喷气间隔角，总共记录了 100 个单独的燃烧循环以解决循环变化。显示整体平均流场以说明详细的流动结构，而使用空间滤波的雷诺分解用于分析湍流强度。结果表明，在较小的射流间距下，体积流幅度和湍流强度降低，这表明在射流撞击壁面后，两个相对的壁面射流头立即碰撞会导致流动抑制效果。这引起了对混合的担忧，因为较低的喷气间距会在喷气相互作用区域产生更多的富含燃料的混合物。尽管流量幅度较低，但对于较窄的射流间距，估计循环变化也较高，这是显着的射流相互作用的另一个缺点。关于射流-旋流相互作用，由于逆流布置抑制了流动，与较窄的相互作用射流间距结果类似，在向上涡流侧穿透的壁射流头显示出较低的整体流动量级。然而，在上升涡流侧测量的湍流强度更高，这表明与穿透壁喷射头相反的相对较弱的涡流矢量实际上可以增强混合。