Abstract In direct-injection engines, the formation of fuel wall film on piston surface and liner wall is a primary cause for emissions of unburnt hydrocarbons and particulate matter. It is therefore important to investigate the behavior and effect of a wall fuel film under typical engine conditions. Following our previous study of wall film effects on flame propagation and quenching under constant thermodynamic conditions (Tao et al. IJER, 2018), more complexities rooted in real engine conditions have been considered in the current work, including two real engine in-cylinder thermodynamic trajectories occurring at catalyst warming (CW) and low-speed high-load (LSHL) conditions, varying fuel wall film thickness accounting for both vaporization and condensation, and the stagnation boundary layer flow over the wall film. To shed light on the role of wall heat transfer, parameter sweeping of wall temperature is conducted from 303 K to 363 K. Two representative wall film models using empirical vaporization rate and gas-liquid interface heat flux are compared with our numerical simulation. A good correlation between vapor boundary thickness and quenching distance has been found. Competition between enhanced vaporization due to tangential convection and aggravate condensation from elevated pressure is also demonstrated. The results lead to useful insights into the behavior of a wall film in real engine in-cylinder thermodynamic conditions and could be used to construct low dimensional empirical wall film models in three-dimensional engine combustion modeling.

中文翻译：

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发动机热力学条件下壁膜效应及火焰淬火的进一步研究

摘要 在直喷发动机中，活塞表面和缸套壁上形成的燃料壁膜是未燃烧碳氢化合物和颗粒物排放的主要原因。因此，研究典型发动机条件下壁面燃料膜的行为和影响非常重要。继我们之前对恒定热力学条件下壁膜对火焰传播和淬火的影响（Tao 等人，IJER，2018 年）的研究之后，目前的工作已经考虑了更多植根于真实发动机条件的复杂性，包括两个真实的发动机缸内热力学在催化剂加温 (CW) 和低速高负载 (LSHL) 条件下发生的轨迹、考虑蒸发和冷凝的燃料壁膜厚度变化以及壁膜上的停滞边界层流动。为了阐明壁面传热的作用，壁面温度的参数扫描从 303 K 到 363 K 进行。使用经验蒸发率和气液界面热通量的两个代表性壁膜模型与我们的数值模拟进行了比较。已经发现蒸汽边界厚度和淬火距离之间有很好的相关性。还证明了由于切向对流导致的增强蒸发与来自高压的加剧冷凝之间的竞争。结果有助于深入了解真实发动机缸内热力学条件下壁膜的行为，并可用于在三维发动机燃烧建模中构建低维经验壁膜模型。使用经验蒸发率和气液界面热通量的两种代表性壁膜模型与我们的数值模拟进行了比较。已经发现蒸汽边界厚度和淬火距离之间有很好的相关性。还证明了由于切向对流导致的增强蒸发与来自高压的加剧冷凝之间的竞争。结果有助于深入了解真实发动机缸内热力学条件下壁膜的行为，并可用于在三维发动机燃烧建模中构建低维经验壁膜模型。使用经验蒸发率和气液界面热通量的两种代表性壁膜模型与我们的数值模拟进行了比较。已经发现蒸汽边界厚度和淬火距离之间有很好的相关性。还证明了由于切向对流导致的增强蒸发与来自高压的加剧冷凝之间的竞争。结果有助于深入了解真实发动机缸内热力学条件下壁膜的行为，并可用于在三维发动机燃烧建模中构建低维经验壁膜模型。还证明了由于切向对流导致的增强蒸发与来自高压的加剧冷凝之间的竞争。结果有助于深入了解真实发动机缸内热力学条件下壁膜的行为，并可用于在三维发动机燃烧建模中构建低维经验壁膜模型。还证明了由于切向对流导致的增强蒸发与来自高压的加剧冷凝之间的竞争。结果有助于深入了解真实发动机缸内热力学条件下壁膜的行为，并可用于在三维发动机燃烧建模中构建低维经验壁膜模型。