初始条件对喷雾火焰着火影响的大涡模拟研究

Effects of Initial Conditions on the Auto-ignition Process for Spray Flames Using Large Eddy Simulation

本文基于LES-LEM模拟方法开展了不同环境温度、压力条件下正庚烷喷雾火焰的大涡模拟研究。首先,通过与ECN喷雾燃烧基础数据库(Engine Combustion Network,ECN)中的实验结果进行对比,发现LE-LEM方法预测的着火延迟期和火焰浮升长度与实验值非常符合。因此,基于此分析了不同发动机工况下喷雾燃烧的着火和燃烧过程。结果显示高温火核首先出现在浓混合气区域,同时,喷雾火焰中同时存在预混和非预混燃烧。计算结果显示燃烧能够使喷雾火焰加速向下游发展,但高环境压力又能抑制喷雾火焰向下游运动。

Large eddy simulation coupled with linear eddy simulation （LES-LEM） is applied for the simulation of n-heptane spray flames at different initial temperatures and ambient gas densities. Firstly, the results under inert condition are compared with the experimental data from the Engine Combustion Network （ECN） website. Good agreement is observed in terms of ignition delay and flame lift-off length. Then the auto-ignition and combustion processes are further analyzed under diesel-engine relevant conditions. Results show that the high-temperature kernels are formed at fuel-rich regions. And both premixed and non-premixed combustion coexist in spray flames. The development of spray flames is accelerated by combustion, but it is prevented further developing downstream by the high pressure of the ambient gas.