喷射策略对乙醇-汽油发动机燃烧和排放的影响

Effect of Injection Strategies on Combustion and Emissions of Ethanol-gasoline Engine

为改善乙醇-汽油发动机的燃烧和排放性能,针对一台乙醇-汽油发动机开展了典型工况下不同喷射策略的试验,对比分析了各种喷射策略和乙醇比例对发动机燃烧和排放的影响.结果表明,燃油消耗率(Brake Specific Fuel Consumption,BSFC)随加权喷射正时中心(T_(COI))提前呈现先下降而后趋于稳定,随喷射次数增加而下降.相比单次喷射,多次喷射使BSFC最大减少7%,一氧化碳和碳氢化合物排放明显降低,但会导致氮氧化物排放略有上升(远小于T_(COI)的影响).汽油掺混乙醇后,燃烧持续期变长,但由于点火正时和燃烧重心提前使发动机热效率明显提升.增大T_(COI)和乙醇比例均可降低一氧化碳体积分数,最大降幅达15%.乙醇比例对碳氢化合物和氮氧化物的影响取决于T_(COI).T_(COI)能很好地表征喷油特性,对排放影响比乙醇比例和喷射次数的影响均大.选取合适的喷射次数、乙醇比例和T_(COI)可显著提高发动机热效率并减少排放.

In order to improve the combustion and emission performance of the ethanol-gasoline engine,the tests on an ethanol-gasoline engine were carried out with different injection strategies under typical working condi⁃tions.The effects of injection strategies and ethanol proportions on engine combustion and emissions were compared and analyzed.The results showed that the Brake Specific Fuel Consumption(BSFC)decreased first and then became stable with T_(COI) in advance,and decreased with the increase of the number of injections.Compared with a single injec⁃tion,multiple injections reduced BSFC by up to 7%,and carbon monoxide and hydrocarbon emissions were obviously reduced,but it led to a slight increase in nitrogen oxide emissions(much less than the impact of T_(COI)).After gasoline was mixed with ethanol,the combustion duration became longer,but the thermal efficiency of the engine was significantly improved due to ignition timing and early combustion center.Increasing the proportion of ethanol and T_(COI) can reduce the carbon monoxide concentration by up to 15%.The effect of ethanol proportion on hydrocarbon and nitro⁃gen oxide depended on the T_(COI).T_(COI) was a good parameter of the injection characteristics,and the impact on emis⁃sions was greater than that of ethanol proportion and number of injections.Selecting the appropriate number of injec⁃tions,ethanol proportion,and T_(COI) can significantly improve engine thermal efficiency and reduce emissions.