Because of the storage and safety of hydrogen on board vehicles, there still exist many problems; this paper introduces a system of hydrogen-rich gases and its application to an electronically controlled spark ignition engine. The hydrogen-rich gases from the designed reformer are produced by methanol dissociated by the heat recycled from the exhaust emissions of an engine. The effects of the hydrogen-rich gases on the performances of the engine were investigated for lean-burning operations. The test results indicate that the engine can operate using a very lean fuel mixture owing to the wide ignition limits of the hydrogen-rich gases. When the excessive air-to-fuel ratio is higher than 1.4, the nitrogen oxide emissions are reduced by 90%, the carbon monoxide emissions are ultra-low, and the hydrocarbon emissions are at nearly the same level as those produced from a gasoline engine. In addition, while maintaining the power output of the engine, lean burning of the hydrogen-rich gases and partial recycling of the exhaust heat significantly improve the brake thermal efficiency of methanol.