Effects of Methanol Direct Injection and High Compression Ratio on the Performances of a Turbocharged Spark-Ignition Engine; [甲醇直喷及高压缩比对点燃式发动机性能的影响]

A turbocharged Miller cycle gasoline direction injection(GDI) engine was modified to a methanol direction injection(MDI) engine with high compression ratio(13.8)，and experimental study was conducted to investigate the effects of MDI on combustion，emission and brake thermal efficiency(BTE) at speed of 2 750 r/min from low to high loads. Results show that MDI gives a shorter combustion duration at middle to high loads(BMEP≥ 0.8 MPa). Low in-cylinder temperature caused by MDI and high octane number of methanol allows the engine operating at the optimum combustion phase without knock occurrence. Furthermore，MDI reduces NOx，CO and HC emissions at different loads，and the unburned fuel loss is reduced by greater than 1% at all loads under the same control parameters. The operating point with the maximum BTE shifts from BMEP＝1.1 MPa of the original engine with a lower compression ratio of 11.5 to BMEP＝1.5 MPa of the MDI engine with higher compression ratio. The maximum BTE under stoichiometric combustion also increases from 37.4% to 42.6% due to lower losses of exhaust heat，heat transfer and unburned fuel loss. The main obstacle to higher BTE is the maximum allowable in-cylinder pressure. © 2023 Chinese Society for Internal Combustion Engines. All rights reserved.