分会场

高效清洁燃烧

摘要

Supercharging is an important technology for high performance internal combustion engines, which may lead to the in-cylinder ambient density increase in the late-cycle compression stroke. In this study, a high-fidelity LES of n-dodecane spray combustion was carried out under various ambient densities (ρamb) ranging from 20 to 60 kg/m3. The results indicate that as ρamb increases, the ignition delay time (IDT) is reduced. However, the induction time between high-temperature and low-temperature ignition remains relatively constant when ρamb surpasses 40 kg/m3. Additionally, under low ρamb conditions, such as ρamb = 20 kg/m3, the HT ignition is induced by a cool-flame wave, marked by the formation and subsequent consumption of CH2O, with the initial HT kernels emerging at the tip of the vapour jet. While as ρamb increases, the cool-flame wave is weakened during the high-temperature induced period. Specifically, at ρamb = 60 kg/m3, the multiple strong HT kernels occur near the spray centre immediately after the low-temperature (LT) ignition, rather than a significant cool-flame wave. Subsequently, these kernels propagate rapidly to the surroundings to complete high-temperature ignition. Furthermore, under the low ambient density conditions, the spray core and low-temperature flame are relatively spatially separated. However, at ρamb = 60 kg/m3, the spray core is almost surrounded by the LT flame, with the HT flame extending to cover not only the LT flame but also the tip of the spray core, yielding a rich lifted-flame combustion with high soot formation.

关键词

Spray;Combustion;Ignition;Diesel;LES

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