Major design features of high-tumble spark-ignition engines achieving over 40% brake thermal efficiency include a sub-square combustion chamber, less curved or more “straight” intake port shape and wider angle between the intake and exhaust valves, which are intended to enhance the turbulence at spark timing and thereby increasing the flame propagation speed. This new design requires a clear understanding of the in-cylinder flow field and its variation due to direct fuel injection into the cylinder. The present study reports a new endoscopic high-speed particle image velocimetry (eHS-PIV) technique implemented in a multi-cylinder high-tumble production engine, which can be used to acquire crucial flow field information in a timely manner with no significant resources required to develop a single-cylinder full optical engine. A laser beam at 35 kHz was inserted through a rigid endoscope (borescope) wherein a series of rod lenses producing a 60° diverging planar laser sheet to cover the pent-roof area. Hollow-glass spherical particles were supplied upstream of the throttle body. A camera borescope was installed to record particle movement at the same 35 kHz framing rate and the acquired movies of 100 cycles were post-processed using PIVLab. The feasibility tests performed in an available single-cylinder full optical engine indicated that the new eHS-PIV is applicable to direct-injection engines with both motoring flow fields and the injection-induced flow structure alteration is clearly visualised. The application of the eHS-PIV to a multi-cylinder production engine was also successful and achieved a finding of new flow structures unique to high-tumble engines and the significant enhancement effects of direct fuel injection on flow velocity and turbulence intensity. Graphic abstract

中文翻译：

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高速翻滚生产发动机中的内窥镜高速粒子图像测速 (eHS-PIV)

实现超过 40% 制动热效率的高滚流火花点火发动机的主要设计特点包括亚方形燃烧室、更少弯曲或更“直”的进气口形状以及进气门和排气门之间的更大角度，旨在增强点火正时的湍流，从而提高火焰传播速度。这种新设计需要清楚地了解缸内流场及其由于直接将燃料喷射到气缸中而引起的变化。本研究报告了一种新的内窥镜高速粒子图像测速 (eHS-PIV) 技术在多缸高翻滚生产发动机中实施，可用于及时获取关键流场信息，无需大量资源开发单缸全光学引擎。将 35 kHz 的激光束插入刚性内窥镜（管道镜），其中一系列棒状透镜产生 60° 发散平面激光片以覆盖五角形屋顶区域。在节气门体的上游供应中空玻璃球形颗粒。安装了照相机管道镜以相同的 35 kHz 帧速率记录粒子运动，并使用 PIVLab 对获取的 100 个周期的电影进行后处理。在可用的单缸全光学发动机上进行的可行性测试表明，新的 eHS-PIV 适用于具有两个机动流场的直喷发动机，并且喷射引起的流动结构变化清晰可见。eHS-PIV 在多缸生产发动机上的应用也取得了成功，并发现了高滚流发动机独有的新流动结构，以及直接燃油喷射对流速和湍流强度的显着增强效果。图形摘要