Twin turbine exhaust gas re-circulation system having a second stage variable nozzle turbine

A method of operating an internal combustion engine, comprising the steps of:

• providing a plurality of combustion cylinders, an intake manifold supplying combustion gas to said plurality of combustion cylinders, and first and second exhaust manifolds;
• transporting exhaust gas from said plurality of combustion cylinders to said first exhaust manifold and said second exhaust manifold;
• providing a first turbocharger including a first turbine having at least one inlet and an outlet, and a first compressor having an inlet and an outlet;
• providing a second turbocharger including a second turbine having a controllable, variable intake nozzle at an inlet and having an outlet, and including a second compressor having an inlet and an outlet;
• rotatably driving said first turbine with exhaust gas introduced at said first turbine at least one inlet from each said second turbine outlet and said first exhaust manifold;
• rotatably driving said second turbine with exhaust gas introduced at said second turbine inlet from said second exhaust manifold;
• introducing combustion gas at said first compressor inlet;
• transporting compressed combustion gas from said first compressor outlet to said second compressor inlet;
• transporting compressed combustion gas from said second compressor outlet to said at least one intake manifold;
• sensing at least one of operating conditions of said engine and performance of said turbochargers;
• and
• controlling said controllable variable intake nozzle in response to at least one of said engine operating conditions and said performance of said turbochargers.

A turbocharger and engine emissions control system for use with an internal combustion engine having a plurality of combustion cylinders, an intake manifold and first and second exhaust manifolds, said turbocharger and engine emissions control system comprising:

• a first turbocharger including a first turbine having at least one inlet and an outlet, and a first compressor having an inlet and an outlet, said at least one first turbine inlet having a fixed geometry and being fluidly coupled with the first exhaust manifold;
• a second turbocharger including a second turbine having an inlet and an outlet, and a second compressor having an inlet and an outlet, said second turbine inlet having a controllable variable inlet nozzle fluidly coupled with said second exhaust manifold, and said second compressor inlet being fluidly coupled with said first compressor outlet;
• and
• an exhaust gas recirculation duct fluidly coupled to said second exhaust manifold and said intake manifold.