正丁醇部分预混燃烧及其颗粒物排放特性试验

An Investigation on the Particulate Size Emissions of Partially Premixed Combustion for n-butanol

通过一台改造的单缸柴油机研究了小负荷下EGR、喷射时刻、进气压力及喷射策略对正丁醇部分预混燃烧(PPC)及其颗粒物排放特性的影响.结果表明:引入适当小比例EGR率能够促进正丁醇着火,提前燃烧相位;正丁醇PPC颗粒物粒径集中在40 nm以内,绝大部分为核态颗粒物;随着EGR率的增大,颗粒物粒径范围加大,但较高EGR率下滞燃期过长,燃烧相位靠后,颗粒物排放的浓度及粒径迅速降低;随着喷射时刻的提前,颗粒物粒径分布先向大粒径、高浓度偏移,后向小粒径、低浓度移动,相同燃烧相位CA 50时,远上止点喷射比近上止点喷射能够获得较小的颗粒物浓度;小负荷下较低进气压力仍具有足够高的空燃比,但其滞燃期长,颗粒物排放浓度低,粒径分布范围窄,增大进气压力使颗粒物粒径分布向大粒径偏移;相对单次喷射,两次喷射策略能够显著降低颗粒物排放浓度,并且主后喷两次喷射策略降低效果更佳.

An experimental investigation on effect of EGR,injection timing,intake pressure and injection strategy on combustion and particulate size distributions of n-butanol partially premixed combustion(PPC)under low loads was conducted in a single cylinder diesel engine.The results indicate that the properly small EGR rate can promote ignition which leads to a forward CA 50.The particulate diameter is less than 40 nm for most of particle emissions,and the most of particle emissions are nucleate mode.The scope of particle diameter broadens as the EGR rate increases,but the concentration and diameter of particulate matter decrease sharply when the EGR rate is too high since the longer ignition delay and retarded CA 50.The curves of particulate size distribution shift toward bigger diameter and higher concentration firstly,and then move toward smaller diameter and lower concentration as the injection timing advances.The particle concentration and diameter at the injection timing closed to top dead center(TDC)are smaller than that at the injection timing far from TDC under the same CA 50.The particle concentration is very low and the scope of particulate size distribution is small for lower intake pressure because of longer ignition delay.And the scope of particle diameter broadens as the intake pressure increases.The particle concentration and size are smaller for the two-state injection strategies compared to single injection strategy,and main-post injection strategy gives the lowest particle concentration among three injection strategy.