This study performs endoscopic high-speed imaging to enhance the fundamental knowledge of in-cylinder flow structure and flame development process in a selected high-tumble production engine. The endoscopic high-speed particle image velocimetry (eHS-PIV) was performed for varied engine speeds and intake valve closing (IVC) timings to evaluate their impact on the in-cylinder flow structure in a motored engine condition. On another endoscope engine sharing the same hardware, high-speed flame imaging was conducted to visualise spark stretch and flame propagation. The flow and flame measurements were repeated for over 100 cycles and the ensemble-averaged results are compared. The eHS-PIV showed that a strong tumble vortex is generated during the piston compression with the flow directed towards the exhaust side. As the piston reaches top dead centre (TDC), however, a complex flow breakup involving multiple flow components occurs. This is followed by lateral flow vectors travelling back towards the intake side, which is termed as the bounce-back flow. For a tested engine speed range of 1700–2700 revolutions per minute (rpm), 2500 rpm shows the most significant bounce-back flow as a result of competition between the remaining exhaust-ward tumble flow strength and the newly formed bounce-back flow strength. At a retarded IVC timing, the flow loss leads to a weakened tumble flow and subsequently no bounce-back flow formation to maintain the exhaust-ward TDC flow direction. From the comparison between the flow results and spark/flame high-speed images, a strong positive correlation is found between the TDC flow direction and spark plasma stretch, and subsequently the flame propagation direction. The findings indicate that the TDC flow direction should be considered as a key parameter in the engine design and operating condition settings.

本研究执行内窥镜高速成像，以增强对选定的高滚流生产发动机的缸内流动结构和火焰发展过程的基础知识。对不同的发动机转速和进气门关闭 (IVC) 正时进行内窥镜高速粒子图像测速 (eHS-PIV)，以评估它们在机动发动机条件下对缸内流动结构的影响。在共享相同硬件的另一个内窥镜引擎上，进行高速火焰成像以可视化火花拉伸和火焰传播。流量和火焰测量重复超过 100 次循环，并比较整体平均结果。eHS-PIV 表明，在活塞压缩过程中会产生强烈的滚流涡流，流向排气侧。然而，当活塞到达上止点 (TDC) 时，会发生涉及多个流动分量的复杂流动分裂。随后是向进气侧返回的侧向流矢量，这被称为回弹流。对于 1700-2700 转/分钟 (rpm) 的测试发动机转速范围，2500 rpm 显示出最显着的反弹流，这是由于剩余的排气侧滚流强度和新形成的反弹流强度之间的竞争. 在延迟的 IVC 正时，流量损失会导致滚流减弱，随后不会形成回弹流以保持排气向 TDC 流动方向。从流动结果和火花/火焰高速图像的比较，发现TDC流动方向和火花等离子体拉伸之间存在很强的正相关，然后是火焰传播方向。研究结果表明，TDC 流向应被视为发动机设计和运行条件设置中的关键参数。