Abstract Partially premixed combustion (PPC) often adopts the early fuel-injection strategy that could result in spray-wall interaction involved with piston top-land crevice. This interaction may produce a significant impact on engine combustion and unburned hydrocarbons (UHC) emission, which is still not well understood. In this study, we investigated the detailed spray-wall interaction and its effects on the two-stage ignition, i.e. low- and high-temperature heat release (LTHR and HTHR), and the in-cylinder spatial UHC distribution of PPC in a full-view optical engine at low engine load. The PRF 70 fuel was used as the gasoline surrogate. The high-speed imaging of the natural flame luminosity was acquired to quantify the flame probability distribution. The qualitative fuel-tracer, formaldehyde, and UHC planar laser-induced fluorescence (PLIF) imaging techniques were employed to reveal the fuel, LTHR and UHC distribution characteristics, respectively. The LTHR, HTHR and UHC distribution formed by the fuel trapped in the piston top-land crevice were visualized by PLIF imaging techniques for the first time. The PLIF results indicate that the main UHC formed in the PPC engine comes from the central part of the cylinder close to the injector nozzle, where the overall equivalence ratio is low and the injector dribbling is an important source of UHC. The UHC formed in the piston crevice of the PPC engine depends on the local equivalence ratio of the fuel trapped in the crevice. When the overall equivalence ratio of the charge in the crevice is relatively high, the trapped fuel undergoes both LTHR and HTHR and produces negligible UHC. However, the UHC from the piston crevice becomes considerable when the fuel injection timing is too early so that an overly lean mixture is generated. Based on the above findings, three implications of the PPC operation at low engine load for low UHC emission and high engine efficiency are proposed.

中文翻译：

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喷壁相互作用对部分预混汽油发动机缸内空间未燃碳氢化合物分布的影响

摘要 部分预混燃烧 (PPC) 通常采用早期燃油喷射策略，这可能会导致活塞顶-陆地缝隙中的喷壁相互作用。这种相互作用可能会对发动机燃烧和未燃烧碳氢化合物 (UHC) 排放产生重大影响，但目前尚不清楚。在这项研究中，我们研究了详细的喷雾壁相互作用及其对两阶段点火的影响，即低温和高温热释放（LTHR 和 HTHR），以及 PPC 的缸内空间 UHC 分布。 - 在低引擎负载下查看光学引擎。PRF 70 燃料用作汽油替代品。获取自然火焰光度的高速成像以量化火焰概率分布。定性燃料示踪剂，甲醛，和 UHC 平面激光诱导荧光 (PLIF) 成像技术分别用于揭示燃料、LTHR 和 UHC 分布特征。PLIF 成像技术首次对活塞顶面缝隙中的燃料形成的 LTHR、HTHR 和 UHC 分布进行了可视化。PLIF结果表明，PPC发动机中形成的主要UHC来自靠近喷油嘴的气缸中心部分，整体当量比较低，喷油器滴流是UHC的重要来源。在 PPC 发动机活塞缝隙中形成的 UHC 取决于被困在缝隙中的燃料的局部当量比。当缝隙中装料的总当量比相对较高时，捕获的燃料同时经历 LTHR 和 HTHR，产生的 UHC 可忽略不计。然而，当燃油喷射时间过早时，来自活塞缝隙的 UHC 会变得相当大，从而产生过稀的混合气。基于上述发现，提出了低发动机负荷下 PPC 运行对低 UHC 排放和高发动机效率的三个影响。