Method for reducing engine exhaust emissions

An apparatus for increasing and maintaining exhaust gas temperature as needed for a desired after-treatment system effectiveness, comprising:

• an engine comprising a plurality of cylinders, one or more of which have a cylinder deactivation mechanism controlled by a controller;
• an air intake manifold connected to the cylinders for providing air to the cylinders;
• an inlet to the intake manifold, said inlet comprising a throttle controlled by the controller;
• an exhaust manifold connected to the cylinders for receiving exhaust gas from the cylinders;
• an exhaust gas pathway connected to the exhaust manifold at one end and vented to the atmosphere at the other end,
• at least one after-treatment device located in the exhaust gas pathway, said after-treatment device having an activation temperature;
• and a sensor located in one of the exhaust manifold, the after-treatment device, or a part of the exhaust gas pathway between the exhaust manifold and the after-treatment device, said sensor providing information to the controller about the temperature of the exhaust gas;
• wherein the controller comprises logic for engaging the one or more of the cylinder deactivation mechanisms during acceleration and cruising as needed to attain the activation temperature and during deceleration or idle to decrease exhaust gas flow rate to maintain the activation temperature.