增压直喷汽油机中润滑油液滴诱发早燃机制的数值研究
Numerical Investigations for Mechanism of Pre？？Ignition Induced by Lubricant Oil Droplets in Supercharged DISI Engines

通过利用多维计算流体动力学(CFD)耦合一个多组分汽油替代物的骨架反应机理,对增压直喷汽油机中润滑油液滴诱发早燃的机制进行了研究。首先,在模拟增压高强化汽油机压缩上止点热力学状态的定容圆柱网格内,研究了润滑油液滴的存在对汽油/空气混合气自燃过程的影响,结果表明:以正庚烷和过氧氢酮分别作为润滑油蒸发产物时润滑油液滴的存在均可缩短混合气的着火延迟时间,尤其是以过氧氢酮作为润滑油蒸发产物时混合气的着火延迟时间缩短更为明显;随着润滑油液滴粒径的增大,混合气的着火延迟时间先缩短后延长,润滑油液滴温度和混合气的温度、压力升高会进一步缩短混合气的着火延迟时间。然后,以过氧氢酮作为润滑油蒸发产物,在增压直喷汽油机动网格内模拟了润滑油液滴存在时缸内混合气的自燃过程,结果表明:润滑油液滴蒸发释放出了着火性能较好的组分,缩短了液滴周围混合气的着火延迟时间,导致液滴周围混合气在火花点火之前自燃,从而引发早燃。最后,根据以上结论提出了一个润滑油液滴诱发早燃的机制。
Multidimensional computational fluid dynamics coupled with a skeletal chemical kinetic model of gasoline substitute is used to investigate the mechanism of pre？？ignition induced by lubricant oil droplets in a supercharged direct？？injection spark？？ignition (DISI) engine under high load and at low speed. The influence of lubricant oil droplet on the auto？？ignition of gasoline and air mixture is evaluated in a constant volume combustion bomb with the thermodynamic conditions similar to those in the DISI engine cylinder at the compression top dead center. The results show that the ignition delay time of gasoline and air mixture is shortened by the presence of lubricant oil droplet when n？？heptane and hydrogen peroxide ketone (C8KET) are used as lubricant oil evaporation substitutes respectively, and this behavior is more obvious when C8KET is used as lubricant oil evaporation substitute. The ignition delay time of gasoline and air mixture first decreases then increases with the increasing lubricant oil droplet diameter. In addition, the ignition delay time of fuel？？air mixture is further shortened with the increasing lubricant oil droplet temperature and the temperature and pressure of the fuel？？air mixture. A numerical investigation for auto？？ignition of gasoline and air mixture with the presence of lubricant oil droplets in the supercharged DISI engine is carried out by using C8KET as lubricant oil evaporation substitute. The results show that the ignition delay time of the fuel？？air mixture around the lubricant oil droplets is shortened by the constituents with good ignition performance evaporating from lubricating oil droplets, which causes auto？？ignition of fuel？？air mixture in this area before the spark ignition and leads to the occurrence of pre？？ignition. A mechanism of pre？？ignition induced by lubricant oil droplets is finally proposed following the conclusions above