米勒循环通过改变配气策略实现膨胀比大于实际压缩比的效果，从而提高发动机的热效率并降低燃油消耗率，因此被认为是改善小型GDI发动机燃油经济性的重要途径之一。然而，关于米勒循环对汽油机燃烧性能影响的微观机制并不明确，因此利用一维仿真软件GT-POWER和三维CFD软件CONVERGE，针对不同米勒循环策略对GDI发动机的进气以及缸内燃烧过程的影响进行了数值模拟研究。结果表明：在中低转速时，进气门早关策略在改善发动机燃油经济性方面要优于进气门晚关策略，同时不会对扭矩造成太大的负面影响；而进气门晚关能够显著提高燃烧过程中的缸内湍动能，增强油气混合过程。此外，在着火后，进气门晚关的缸内整体温度比进气门早关的低，同时高温区域较小，因此在抑制发动机爆震方面的能力要优于进气门早关策略。

Miller cycle can improve the thermal efficiency and brake specific fuel consumption by changing the gas distribution strategy to make the expansion ratio greater than the actual compression ratio and is hence considered as one of the important ways to improve the fuel economy of small GDI engine. However, the microscopic mechanism about the effect of Miller cycle on the combustion performance of gasoline engine is not clear. So the effects of different Miller cycle strategies on the intake and in-cylinder combustion processes of GDI engine were studied based on numerical simulation by using 1D GT-POWER software and 3D CFD CONVERGE software. The results show that the early intake valve closing (EIVC) strategy is better than the late intake valve closing (LIVC) strategy in improving the engine fuel economy at low and medium speeds, without much negative impact on the torque. The LIVC strategy can significantly increase the in-cylinder turbulence energy during combustion and hence improve the fuel-gas mixing process. In addition, the overall in-cylinder temperature is lower and the hightemperature region is smaller for the LIVC strategy after ignition, so it is better than the EIVC strategy in suppressing engine knocking.