Abstract: The test was conducted on an ethanol fueled spark-ignition engine with low proportion of dimethyl ether.An electronically controlled dimethyl ether injection system was used in the test to ensure that ethanol and dimethyl ether were injected into the intake ports together.The dimethyl ether volume fraction increased from O to 3%by adjusting the dimethyl ether injection duration under an engine speed of 1 800 r/min,the intake manifold absolute pressure(MAP)of 61.5 kPa,and two excess air ratios of1.0 and 1.1,respectively.The experimental results show that the indicated thermal efficiency is improved,cyclical fluctuation is reduced,CO and HC emissions are dropped whereas NO_x slightly increases at different excess air ratios with the addition of dimethyl ether.