EGR cylinder operation in an internal combustion engine

A system, comprising:

• an internal combustion engine having a plurality of cylinders that receive a charge flow from an intake manifold;
• at least one of the plurality of cylinders comprising a primary EGR cylinder that is in flow communication with an EGR exhaust manifold, the primary EGR cylinder comprising at least one intake valve and at least one exhaust valve;
• remaining ones of the plurality of cylinders being in flow communication with an exhaust manifold that is flow connected to an exhaust passage that emits exhaust gas from the remaining ones of the plurality of cylinders;
• a controller configured to determine an exhaust pressure condition in the EGR exhaust manifold and, in response to the exhaust pressure condition, dynamically increase a compression ratio of the at least one primary EGR cylinder relative to a compression ratio of the remaining ones of the plurality of cylinders to reduce exhaust gas residuals in the at least one primary EGR cylinder;
• wherein during operation the at least one exhaust valve of the primary EGR cylinder is configured to close relative to an opening of the at least one intake valve of the primary EGR cylinder at initiation of an intake stroke of a piston of the primary EGR cylinder so that a first overlap in the opening of the at least one exhaust valve and the at least one intake valve is less than a second overlap in an open position of an exhaust valve and an open position of an intake valve at initiation of an intake stroke in each of the remaining ones of the plurality of cylinders to reduce backflow of exhaust gases from the EGR manifold to the intake manifold through the primary EGR cylinder;
• and
• wherein during operation the at least one exhaust valve of the primary EGR cylinder is configured to close before top dead center of the piston of the primary EGR cylinder at initiation of the intake stroke of the primary EGR cylinder and the at least one intake valve of the primary EGR cylinder is configured to open after top dead center of the piston during the intake stroke of the primary EGR cylinder so that the second overlap in the opening of the exhaust valve and the opening of the intake valve is less than zero crank angle degrees while the remaining ones of the plurality of cylinders are configured to operate with a first overlap in an open position of an exhaust valve of a respective cylinder with an open position of an intake valve of the respective cylinder at initiation of an intake stroke of the respective cylinder.

A system, comprising:

• an internal combustion engine having a plurality of cylinders that receive a charge flow from an intake manifold;
• at least one of the plurality of cylinders comprising a primary EGR cylinder that is in flow communication with an EGR exhaust manifold, the primary EGR cylinder comprising at least one intake valve and at least one exhaust valve;
• remaining ones of the plurality of cylinders being in flow communication with an exhaust manifold that is flow connected to an exhaust passage that emits exhaust gas from the remaining ones of the plurality of cylinders, wherein the remaining ones of the plurality of cylinders are configured to operate with a first overlap in an open position of an exhaust valve of a respective cylinder with an open position of an intake valve of the respective cylinder at initiation of an intake stroke of the respective cylinder;
• a controller configured to determine an exhaust pressure condition in the EGR exhaust manifold and, in response to the exhaust pressure condition, dynamically increase a compression ratio of the at least one primary EGR cylinder relative to a compression ratio of the remaining ones of the plurality of cylinders to reduce exhaust gas residuals in the at least one primary EGR cylinder,
• wherein during operation the at least one exhaust valve of the primary EGR cylinder is configured to close before top dead center of a piston of the primary EGR cylinder relative to an opening of the at least one intake valve of the primary EGR cylinder after top dead center of the piston of the primary EGR cylinder at initiation of an intake stroke so that a second overlap in the opening of the at least one exhaust valve and the at least one intake valve is less than the zero crank angle degrees to reduce backflow of exhaust gases from the EGR exhaust manifold to the intake manifold through the at least one primary EGR cylinder, while each of the remaining ones of the plurality of cylinders are operated with the first overlap in the open position of the exhaust valve and the open position of the intake valve at initiation of the intake stroke thereof;
• wherein the primary EGR cylinder includes a first compression ratio and the remaining ones of the plurality of cylinders include a second compression ratio, the second compression ratio being less than the first compression ratio, wherein the at least one intake valve of the primary EGR cylinder is connected to a variable valve actuation mechanism that is operable to vary an effective compression ratio of the primary EGR cylinder;
• and
• wherein the effective compression ratio of the primary FOR cylinder is less than the first compression ratio and greater than the second, compression ratio.

A method, comprising:

• operating an internal combustion engine having a plurality of cylinders;
• recirculating exhaust gas from at least one primary FOR cylinder of the plurality of cylinders to an intake of the plurality of cylinders while producing exhaust gas from remaining ones of the plurality of cylinders into an exhaust system including an aftertreatment device;
• determining an exhaust pressure condition in an exhaust manifold of the at least one primary EGR cylinder;
• in response to the exhaust pressure condition, dynamically increasing a compression ratio of the at least one primary EGR cylinder relative to a compression ratio of the remaining ones of the plurality of cylinders to reduce exhaust gas residuals in the at least one primary EGR cylinder;
• reducing the compression ratio of the at least one primary EGR cylinder to an effective compression ratio, wherein the effective compression ratio is greater than the compression ratio of the remaining ones of the plurality of cylinders;
• and
• closing at least one exhaust valve of the at least one primary EGR cylinder before top dead center of a piston of the at least one primary EGR cylinder at initiation of an intake stroke of the at least one primary EGR cylinder and opening at least one intake valve of the primary EGR cylinder after top dead center of the piston during the intake stroke of the at least one primary EGR cylinder so that a first overlap in the opening of the exhaust valve and the opening of the intake valve is less than zero crank angle degrees to reduce backflow of exhaust gases through the at least one primary EGR cylinder while each of the remaining ones of the plurality of cylinders are operated with a second overlap in an open position of an exhaust valve of a respective cylinder with an open position of an intake valve of the respective cylinder at initiation of an intake stroke of the respective cylinder.

A method, comprising:

• operating an internal combustion engine having a plurality of cylinders;
• recirculating exhaust gas from at least one primary EGR cylinder of the plurality of cylinders to an intake of the plurality of cylinders while producing exhaust gas from remaining ones of the plurality of cylinders into an exhaust system having an aftertreatment device, wherein each of the plurality of cylinders includes at least one intake valve and at least one exhaust valve;
• determining an exhaust pressure condition in an exhaust manifold of the at least one primary EGR cylinder;
• in response to the exhaust pressure condition, dynamically increasing a compression ratio of the at least one primary EGR cylinder relative to a compression ratio of the remaining ones of the plurality of cylinders to reduce exhaust gas residuals in the at least one primary EGR cylinder;
• operating respective ones of the remaining ones of the plurality of cylinders with a first overlap in an opening of the least one exhaust valve thereof and an opening of the intake valve thereof relative to an initiation of an intake stroke of a piston of the respective cylinder;
• and
• operating the at least one primary EGR cylinder with a second overlap in an opening of the at least one exhaust valve thereof and an opening of the at least one intake valve thereof relative to an initiation of an intake stroke of a piston of the at least one primary EGR cylinder, wherein the second overlap is less than the first overlap and each of the remaining ones of the plurality of cylinders are operated with the first overlap while the at least one primary FOR cylinder is operated with the second overlap;
• and
• wherein the second overlap includes the at least one exhaust valve and the at least one intake valve being closed simultaneously during a crank angle change range of less than zero and up to negative 20 degrees relative to the initiation of the intake stroke.