An exhaust emission control system of an engine, including an NO.sub.x catalyst disposed in an exhaust passage for storing NO.sub.x within exhaust gas when an air-fuel ratio of the exhaust gas is lean, and reducing the stored NO.sub.x when the air-fuel ratio is approximately stoichiometric or rich, is provided. The system includes an SCR catalyst disposed in the exhaust passage downstream of the NO.sub.x catalyst and for purifying NO.sub.x within exhaust gas by causing a reaction with ammonia, a controller executing a NO.sub.x reduction controlling module for executing a control in which the air-fuel ratio is controlled to a target air-fuel ratio so that the stored NO.sub.x is reduced, and an ammonia adsorption amount acquiring module for acquiring an ammonia adsorption amount of the SCR catalyst by detection or estimation. The NO.sub.x reduction controlling module controls the target air-fuel ratio to be leaner as the ammonia adsorption amount increases.

An exhaust emission control system of an engine is provided, which includes a NO.sub.x catalyst disposed in an exhaust passage for storing NO.sub.x within exhaust gas when an air-fuel ratio of the exhaust gas is lean, and reducing the stored NO.sub.x when the air-fuel ratio is approximately stoichiometric or rich. A processor executes a NO.sub.x reduction controlling module for performing a NO.sub.x reduction control in which a fuel injector performs a post injection to control the air-fuel ratio to a target ratio, and an EGR controlling module for controlling an EGR valve to recirculate EGR gas. In the NO.sub.x reduction control, the EGR controlling module controls an opening of the EGR valve to a target opening smaller than when the NO.sub.x reduction control is not performed. The NO.sub.x reduction controlling module starts the control after the EGR valve opening is controlled to the target opening.

An exhaust emission control system of an engine is provided, which includes a NO.sub.x catalyst disposed in an exhaust passage for storing NO.sub.x within exhaust gas when an air-fuel ratio of the exhaust gas is lean, and reducing the stored NO.sub.x when the air-fuel ratio is approximately stoichiometric or rich. A processor executes a NO.sub.x reduction controlling module for performing, when the NO.sub.x stored amount exceeds a given amount, a NO.sub.x reduction control in which a fuel injector performs a post injection of fuel to continuously control the air-fuel ratio to a target ratio so that the stored NO.sub.x is reduced to be below a given amount, the target air-fuel ratio being a ratio at which the stored NO.sub.x is reducible, the post injection causing the injected fuel to combust inside a cylinder, the execution of the control permitted when an engine load is within a medium load range.

The invention relates to a method for operating an internal combustion engine, wherein the internal combustion engine includes at least one combustion chamber in which a fuel is at least partially burned with ambient air, an exhaust tract that is coupled to an outlet side of the at least one combustion chamber in a fluid communicating manner, wherein hydrogen is used as fuel for the internal combustion engine, wherein the internal combustion engine also has at least one NOx storage catalyst and an exhaust gas discharged from the at least one combustion chamber into the exhaust tract at least partially, preferably entirely, flows through the at least one NOx storage catalyst, wherein a lean hydrogen-air mixture is burned in the at least one combustion chamber in a first operating state, wherein the NOx storage catalyst is regenerated in a second operating state. In order to easily operate the internal combustion engine as a low-emissions system, a rich hydrogen-air mixture is burned in the at least one combustion chamber in the second operating state.

A method and apparatus are disclosed for controlling the operation of an aftertreatment system for a motor vehicle having a Lean NO.sub.x Trap and a tail pipe for conveying exhaust gasses from the LNT to the external environment. Values are calculated for a NO.sub.x content in the exhaust gasses flowing in the tail pipe and the quantity of NO.sub.x stored in the LNT. A DeNO.sub.x request index is calculated as a function of these values. A raw threshold value of the DeNO.sub.x request index is calculated as a function of a LNT temperature and of an exhaust gas mass flow. A corrected threshold value of the DeNO.sub.x request index is calculated as a function of the raw threshold value of the DeNO.sub.x request index and of a correction factor. A DeNO.sub.x regeneration is initiated when the calculated value of the DeNO.sub.x request index is larger than the corrected threshold value.

A fuel control module controls fuel injection of an engine based on a predetermined lean air/fuel ratio. The predetermined lean air/fuel ratio is fuel lean relative to a stoichiometric air/fuel ratio for the fuel. A cylinder control module selectively deactivates opening of intake and exhaust valves of M cylinders of the engine to increase removal of nitrogen oxide (NOx) from exhaust. M is an integer greater than 0 and less than a total number of cylinders of the engine. The fuel control module further: disables fueling of the M cylinders while opening of the intake and exhaust valves of the M cylinders is deactivated; and, while fueling of the M cylinders is disabled and opening of the intake and exhaust valves of the M cylinders is deactivated, controls fuel injection of other cylinders based on a predetermined rich air/fuel ratio that is fuel rich relative to the stoichiometric air/fuel ratio.

A method for regenerating a lean NOx trap (LNT) of an exhaust purification system having the LNT and a selective catalytic reduction (SCR) catalyst includes determining whether a regeneration release condition of the LNT is satisfied; determining whether a regeneration demand condition of the LNT is satisfied; and performing regeneration of the LNT if the regeneration release condition of the LNT and the regeneration demand condition of the LNT are satisfied, wherein satisfaction of the regeneration release condition of the LNT is determined based on an NOx amount absorbed in the LNT, an NH3 amount stored in the SCR catalyst and temperature at an upstream of the SCR catalyst.

A method of predicting the future use of a vehicle or an engine of the vehicle is used to evaluate whether NOx slippage from a lean NOx trap is likely to occur during a current drive cycle and also for scheduling when favorable conditions are likely to exist to purge the lean NOx trap before the slippage of NOx from the lean NOx trap is expected to occur.

A control method for improving nitrogen oxide purification performance (NO.sub.x) includes starting NO.sub.x regeneration, comparing first and second lambda values measured at first and second lambda sensors in a control unit, checking the lean NO.sub.x trap (LNT) temperature, and measuring a second time that has elapsed after the first and second lambda values are found to be the same, and checking whether the second time is greater than or equal to a predetermined time when it is observed that the temperature of the LNT is greater than or equal to the predetermined temperature value.

In an internal combustion engine, a hydrocarbon feed valve and an exhaust purification catalyst are arranged in an engine exhaust passage. A first NOX removal method which injects hydrocarbons from the hydrocarbon feed valve within a predetermined range of period so that the reducing intermediate generated thereby reduces the NOX contained in the exhaust gas and a second NOX removal method which makes the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst a first target rich air-fuel ratio by a period which is longer than this predetermined range are used. When the NOX removal method is switched from the second NOX removal method to the first NOX removal method, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is made a second target air-fuel ratio which is smaller than the first target rich air-fuel ratio.