【摘要】 将一台增压直喷米勒循环汽油机改制成高压缩比（13.8）甲醇直喷点燃式发动机，在2 750 r/min、平均有效压力（brake mean effective pressure, BMEP）为1.1 MPa及1.5 MPa工况下研究了稀燃对甲醇直喷发动机燃烧、排放及热效率的影响。结果表明：随过量空气系数λ增大，甲醇直喷发动机滞燃期和燃烧持续期逐渐延长，高稀释率下燃烧滞燃期和持续期明显短于汽油原机。在1.1 MPa BMEP工况下，发动机的稳定燃烧极限从汽油原机的λ=1.5拓宽到甲醇直喷的1.7以上。气体排放方面，随λ增大，甲醇直喷发动机HC排放逐渐增加，而CO排放先降低后升高，在λ=1.1附近CO排放最低。与汽油原机相比，甲醇直喷发动机在各过量空气系数下均表现出更低的NOx、HC及CO排放。热效率方面，发动机在BMEP为1.1 MPa下，汽油原机和甲醇直喷的最大有效热效率分别为39.8%和44.1%，热效率绝对值分别较当量比燃烧提升2.5%和3.2%。BMEP提高到1.5 MPa后，甲醇直喷发动机在λ=1.4实现了44.5%的最大有效热效率。更多还原

【Abstract】 A turbocharged Miller cycle gasoline direction injection(GDI) engine was modified to a methanol direct injection(MDI) engine with high compression ratio(13. 8), and experimental study was conducted to investigate the effects of lean burn on engine performance and emissions at speed of 2 750 r/min and brake mean effective pressure(BMEP) of 1. 1 MPa and 1. 5 MPa. Results show that ignition delay and combustion duration of MDI extends as combustion excess ratio （λ） increases, and MDI shows much shorter ignition delay and combustion duration than that of original GDI engine at high dilution rate. The stable combustion limit extends from λ =1. 5 of original GDI engine to above 1. 7 of MDI engine. As to gas emissions, lean burn leads to higher HC emission, while the CO emissions show a trend of first decreasing and then increasing and reach the minimum value at λ of about 1. 1. CO, HC and NOx emissions of MDI engine are always lower than that of original GDI engine. As to thermal efficiency, the maximum brake thermal efficiency(BTE) of original GDI and modified MDI engine at load of 1. 1 MPa reaches 39. 8% and 44. 1%respectively, which increases by 2. 5% and 3. 2% when compared with that of stoichiometric combustion. As load increases from 1. 1 MPa to 1. 5 MPa, the maximum BTE reaches 44. 5% with λ equals 1. 4.更多还原