Exhaust emission control method and system

摘要

An exhaust emission control method for treating exhaust gas emitted from an internal combustion engine is provided in which an emission control device located in an exhaust gas passage of the engine stores SOx when the air/fuel ratio of exhaust gas is lean, and releases the stored SOx when the temperature of the emission control device is raised to a desulfurization temperature or higher and the air/fuel ratio of the exhaust gas becomes substantially equal to the stoichiometric air/fuel ratio or rich. In the method, a temperature control process is performed to control the temperature of the emission control device to be within a predetermined temperature range whose lower limit is substantially equal to or higher than the desulfurization temperature, and a desulfurization process is performed to release sulfur from the emission control device by controlling the air/fuel ratio of the exhaust gas to be substantially equal to the stoichiometric air/fuel ratio or rich when the temperature of the emission control device is within the predetermined temperature range. In the method, the temperature control process and the desulfurization process are repeated when sulfur is to be released from the emission control device.