An electronically controled compressed natural gas (CNG) injection system has been developed based on a single-cylinder gasoline engine.The design of CNG supply system,the improvement of ignition system,the optimization of compression ratio,the configuration of the control system and the calibration of the control parameters are introduced.Dynamometer tests show that the volumetric effiency and the power output are greatly improved with the help of the in-cylinder,direct-injected technology.