Experimental Study on Evaporation Characteristics of Light Cycle Oil Droplet under Various Ambient Conditions

The authors conducted droplet evaporation experiments of light cycle oil (LCO) at various ambient temperatures and pressures. Five kinds of LCO and three kinds of arranged fuels were used. We investigated the evaporation characteristics of LCO and the relationships between the evaporation characteristics and the cetane index. In addition to that, a surrogate fuel composed of four chemical species, which can simulate the droplet evaporation characteristics of LCO, was suggested. Experimental results show that the differences in droplet lifetime between fuel species become larger with decreasing ambient temperature. This is because the low volatile component made the evaporation rate outstandingly slow at a low ambient temperature. It was found that the relationship between droplet lifetime and the late-stage distillation temperature becomes stronger at low ambient temperature and high ambient pressure. By an analysis employing the properties of chemical species in LCO surrogate fuel, it is clarified that the mass evaporation rate becomes smaller than the internal diffusion, which is the condition similar to that in the distillation test. Finally, the relationship between the droplet lifetime and the cetane index was investigated. It can be concluded that the droplet lifetime is independent of the cetane index under all conditions tested in this study. The experimental data obtained by this research can be utilized for the validation of multicomponent fuel droplet evaporation models in the future.研究团队开展了不同环境温度与压力下的轻循环油（light cycle oil, LCO）液滴蒸发实验。本次实验共使用5种轻循环油试样与3种配制燃料。本研究探究了轻循环油的蒸发特性，以及该蒸发特性与十六烷值指数（cetane index）之间的关联。 除此之外，本研究还提出了一种由四种化学组分构成的替代燃料（surrogate fuel），该燃料可复现轻循环油的液滴蒸发特性。实验结果表明，随着环境温度降低，不同燃料试样的液滴寿命差异会逐渐增大。究其原因，低挥发性组分在低温环境下会显著延缓蒸发速率。研究发现，在低温环境与高压环境下，液滴寿命与后期蒸馏温度之间的关联会更为显著。 通过对轻循环油替代燃料中各化学组分特性的分析，本研究明确：当质量蒸发速率小于内部扩散速率时，该工况与蒸馏试验（distillation test）中的条件相似。最后，本研究探究了液滴寿命与十六烷值指数之间的关联，可得出结论：在本实验测试的所有工况下，液滴寿命与十六烷值指数均无相关性。本研究获取的实验数据，未来可用于多组分燃料液滴蒸发模型（multicomponent fuel droplet evaporation models）的验证工作。