Effects of Dilution Combustion and Miller Cycle on the Performance of Gasoline Engine

摘要

Dilution and Miller cycle are effective ways to reduce fuel consumption. Based in a 4-cylinder, 4-stroke, turbocharged, low pressure EGR, in-cylinder direct injection gasoline engine, with two intake camshaft angle (133 degrees CA, 170 degrees CA), the effects of dilution (lean combustion, EGR) and Miller cycle on combustion and fuel economy at the minimum fuel consumption (2750 rpm, 11 bar) were studied. Besides, 1D engine simulation and 3D flow simulation are used to study the difference of combustion modes. When COVimep is less than 3 %, the BSFC of EGR is lower than that of lean combustion at the same dilution rate. The dilution limit of lean combustion is larger than EGR. When the dilution rates of EGR and lean combustion are 22 % and 35.9 %, respectively, the BSFC reaches the minimum, which decreases by 4.7 % and 7.2 % respectively. The specific heats ratio of lean combustion is larger than EGR, so the theoretical thermal efficiency of lean combustion is higher. Miller cycle reduces intake time and intake valve lift, which result in the tumble ratio and turbulent kinetic energy decrease significantly. EGR has greater fuel-saving potential for Otto cycle engine than Miller cycle.