发动机缸内自燃着火与火焰传播的调控

Optical Diagnostics on Combustion Mode Between Auto-Ignition and Flame Propagation in Engines

在一台轻型光学发动机上对比了部分预混压燃(PPC)和燃料活性控制压燃(RCCI)两种燃烧模式的着火及燃烧发展过程,并分别探究了不同喷射策略对两种燃烧方式的影响.研究发现,对于PPC燃烧模式,混合气浓度分层越小,燃烧过程中自燃占比越高;混合气浓度分层越大,燃烧过程中火焰传播占比越高.对于RCCI燃烧模式,缸内直喷高活性燃料比例较高时,燃烧是从高活性区到低活性区分阶段顺序自燃;缸内直喷高活性燃料比例较低时,燃烧是火焰传播与自燃共同主导的过程.从而阐明了PPC和RCCI相较于均质压燃(HCCI)能够实现更高负荷高效清洁燃烧的本质是,燃烧发展历程从单纯的多点自燃燃烧转变为火焰传播与自燃共存.

The ignition and flame development process of partially premixed combustion(PPC)mode and reactivity controlled compression ignition(RCCI)mode was compared on a light-duty optical engine.The influence of different injection strategies on combustion mode was also studied.Results show that for PPC mode,the smaller the stratification of mixture concentration is the higher the proportion of auto-ignition in the combustion process.The larger the stratification of mixture concentration is the higher the proportion of flame propagation accounts in the combustion process.For RCCI combustion mode,when the ratio of high active fuel injected directly in cylinder is higher,the combustion process presents a sequential auto-ignition from high reactivity zone to low reactivity zone.When the ratio of high active fuel injected directly in cylinder is lower,the combustion process is controlled by both flame propagation and auto-ignition.Thus,it is clarified that,the root cause that PPC and RCCI modes can achieve higher efficiency and cleaner combustion than homogenous charge compression ignition(HCCI)mode is that the combustion development process changes from the simple multiple auto-ignition combustion to the coexistence of flame propagation and auto-ignition.