为了研究甲醇替代比和过量空气系数对复合喷射发动机稀薄燃烧及排放特性的影响，本研究基于1台自行改造的包含甲醇进气道喷射和汽油缸内喷射（MPI+GDI）的光学复合喷射系统发动机，建立三维仿真模型，进行缸压试验验证，研究稀薄燃烧条件下不同过量空气系数和甲醇替代比下缸内燃烧和排放特性。研究结果表明：随着过量空气系数的增大，火焰传播变慢，放热率峰值出现也晚，后燃现象增强，缸内压力峰值降低且相位推迟，指示热效率呈上升趋势；CO和NOx排放下降，未燃碳氢化合物（THC）排放先降后升，过量空气系数为1.4时最低，原因是适当增加过量空气系数可使燃烧更充分，但是过量空气系数过大导致燃烧不稳定。随着甲醇替代比增加，缸内压力峰值不断增加且相位提前，高甲醇比例的燃料燃烧速度快，燃烧重心前移，排气温度降低，NOx排放增加，THC排放先降后升，CO排放降低。研究结果为甲醇汽油复合喷射发动机的参数优化设计提供了理论依据。

In order to study the effects of methanol substitution ratio and excess air coefficient on the lean combustion and emission characteristics of a combined injection engine, a 3D simulation model was built based on a self-modified engine with an optical combined injection system comprised of methanol inlet injection and gasoline in-cylinder injection (MPI+GDI). The cylinder pressure tests were conducted and the in-cylinder combustion and emission characteristics were studied based on different excess air coefficients and methanol substitution ratios under lean combustion conditions. The results show that the flame propagation becomes slower, the peak of heat release rate appears later, the afterburning phenomenon increases, the peak of in-cylinder pressure decreases and the phase delays, and the indicated thermal efficiency tends to increase with the increase of excess air coefficient. Besides, CO and NO_x emissions reduce and unburned hydrocarbon (THC) emissions first decrease and then increase and reach the lowest at the excess air coefficient of 1.4 because the appropriate increase of excess air coefficient is beneficial to complete combustion and the great increase will lead to unstable combustion. With the increase of methanol substitution ratio, the peak of in-cylinder pressure increases and the phase advances, the fuel with a high methanol ratio burns faster, the mass center of combustion shifts forward, the exhaust temperature decreases, NO_x emissions increase, THC emissions first reduce and then increase, and CO emissions reduce. The results of study provide a theoretical basis for the optimization and design of methanol-gasoline combined injection engine.