The present study intends to explore the in-cylinder combustion and evolution of soot emission during the transition from conventional compression ignition (CI) combustion to partially premixed combustion (PPC) under low load conditions. In-cylinder combustion images and engine-out emissions were measured in an optical engine fueled with low octane heavy naphtha fuel (RON = 50). Full cycle engine simulations were performed using a three-dimensional computational fluid dynamics code CONVERGE, coupled with gas-phase chemical kinetics, turbulence, and a particulate size mimic soot model. The simulations were performed under low load conditions (indicated mean effective pressure (IMEP) of ∼2–3 bar) at an engine speed of 1200 rpm. The start of injection (SOI) was advanced from late (−10 CAD aTDC) to early fuel injection timings (−40 CAD aTDC) to realize the combustion transition from CI combustion to PPC. The simulation results of combustion and emission are compared with the experimental results in both CI and PPC combustion modes. The results of the study show a typical low-temperature stratified lean combustion in PPC mode, while high-temperature spray-driven combustion is evident in CI mode. The in-cylinder small intermediates species such as acetylene (C₂H₂), propargyl (C₃H₃), cyclopentadienyl (C₅H₅), and polycyclic aromatic hydrocarbons (PAHs) were significantly suppressed at PPC mode. Nucleation reaction of PAHs collision contributed to main soot mass production. The distribution of soot mass and particle number density was consistent with the distribution of high-temperature zones in CI and PPC combustion modes.

中文翻译：

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从常规压缩点火（CI）模式过渡到部分预混合燃烧（PPC）模式的缸内燃烧和烟尘演变

本研究旨在探讨在低负荷条件下从常规压缩点火（CI）燃烧过渡到部分预混燃烧（PPC）的过程中的缸内燃烧和烟尘排放的演变。在以低辛烷值重石脑油燃料（RON = 50）为燃料的光学发动机中测量缸内燃烧图像和发动机排出的废气。使用三维计算流体动力学代码CONVERGE进行全循环发动机仿真，并结合气相化学动力学，湍流和微粒模拟烟灰模型。模拟是在低负载条件（指示平均有效压力（IMEP）约为2-3 bar）下以1200 rpm的发动机转速进行的。喷射开始（SOI）从晚期（-10 CAD aTDC）提前到早期燃料喷射正时（-40 CAD aTDC），以实现从CI燃烧到PPC的燃烧过渡。将燃烧和排放的模拟结果与CI和PPC燃烧模式下的实验结果进行了比较。研究结果表明，在PPC模式下，典型的低温分层稀薄燃烧，而在CI模式下，高温喷雾驱动的燃烧明显。缸内小中间体物种，例如乙炔（C 在CI模式下，高温喷雾驱动的燃烧非常明显。缸内小中间体物种，例如乙炔（C 在CI模式下，高温喷雾驱动的燃烧非常明显。缸内小中间体物种，例如乙炔（C₂ ħ ₂），炔丙基（C ₃ H ^ ₃），环戊二烯基（C ₅ H ^ ₅），和多环芳香烃（PAHs）在PPC模式被显著抑制。PAHs碰撞的成核反应促进了主要烟灰的产生。在CI和PPC燃烧模式下，烟尘质量和颗粒数密度的分布与高温区的分布一致。