Embodiments for controlling an exhaust back-pressure valve are provided. In one example, a method for operating an engine comprises closing an exhaust back-pressure valve in response to a component temperature, adjusting intake and/or exhaust valve operation in response to closing the exhaust back-pressure valve to reduce cylinder internal exhaust gas recirculation (EGR), and while the exhaust back-pressure valve is closing, indicating degradation of an exhaust back-pressure system if a designated engine operating parameter remains constant. In this way, degradation of the exhaust back-pressure system may be diagnosed while maintaining combustion stability.

A control device of a spark-ignition engine is provided. The control device includes a main body of the engine, a fuel injection valve, an ignition plug, and a controller. According to an engine operating state, the controller switches between a compression-ignition mode in which compression-ignition combustion is performed, and a spark-ignition mode in which spark-ignition combustion is performed. The controller switches from the spark-ignition mode to the compression-ignition mode by performing in order, a first stage where an air-fuel ratio of mixture gas is set to a predetermined value and the spark-ignition combustion is performed, a second stage where the air-fuel ratio of the mixture gas is set leaner than the first stage and the compression-ignition combustion is performed, and a third stage where the air-fuel ratio of the mixture gas is set richer than the second stage and the compression-ignition combustion is performed.

A method and system for improving starting of an engine is presented. In one example, the method selects a first cylinder to receive fuel since engine stop the cylinder's position relative to the cylinder's top-dead-center compression stroke. The method also describes adjusting a number of fuel injections for a first combustion event since engine stop.

A method and system for improving starting of an engine is presented. In one example, the method selects a first cylinder to receive fuel since engine stop the cylinder's position relative to the cylinder's top-dead-center compression stroke. The method also describes adjusting a number of fuel injections for a first combustion event since engine stop.

Systems and methods for improving combustion in a highly exhaust gas diluted engine are disclosed. The methods and systems may be provided in an engine that includes independent control of cylinder valves with respect to other cylinder valves.

In one embodiment an engine system includes a cylinder, an inlet valve configured to control the flow of gases into the cylinder, an outlet valve configured to control the flow of gases out of the cylinder, a throttle configured to control the flow of fuel into the cylinder, a memory including program instructions stored therein, and a processor operably connected to the inlet valve, the outlet valve, the throttle, and the memory, and configured to execute the program instructions to control the inlet valve and the outlet valve in accordance with an HCCI valve lift profile and an SI valve open/close profile, and activate a first spark in the cylinder while controlling the inlet valve and the outlet valve in accordance with the HCCI valve lift profile and the SI valve open/close profile.

A method for operating an internal combustion engine. The internal combustion engine has multiple cylinders and the cylinders are assigned a respective exhaust valve and intake valve. The internal combustion engine has a crankshaft, an intake camshaft, and an exhaust camshaft. Initially, the internal combustion engine is operated in a first operating state. A second operating state of the internal combustion engine is set by the intake camshaft being adjusted late relative to the crankshaft in comparison to the first operating state and the exhaust camshaft being adjusted early relative to the crankshaft in comparison to the first operating state. To set the second operating state, the intake camshaft is adjusted late by a first value which is in a range from 50-120 crank angle degrees and the exhaust camshaft is adjusted early by a second value which is in a range of 1-35 crank angle degrees.

A variable combustion system for an internal combustion engine, which suppresses mechanical compression ratio change control by a variable mechanical compression ratio control mechanism and carries out internal EGR amount change control by a variable valve actuating control mechanism on a preferential basis in a first operating region in which a compression self-ignition combustion is carried out, and which suppresses the internal EGR amount change control by the variable valve actuating control mechanism and carries out the mechanical compression ratio change control by the variable mechanical compression ratio control mechanism on a preferential basis in a second operating region in which a spark ignition combustion is carried out.

Methods and systems are provided for cleaning out condensate stored at a charge air cooler. In response to increased condensate accumulation at a charge air cooler, airflow through the engine is increased to purge the condensate while an engine actuator is adjusted to maintain engine torque. Combustion stability issues of engine cylinders are addressed by adjusting fueling of each cylinder individually during condensate ingestion.

Various methods and systems are provided for reducing cylinder-to-cylinder variation in exhaust gas recirculation. In one embodiment, a system comprises a first cylinder group of an engine having a first number of cylinders, a second cylinder group of the engine having a second number of cylinders that is not an integer multiple of the first number of cylinders, and an exhaust system coupled to the first cylinder group and the second cylinder group. In at least one mode of operation, the exhaust system has exhaust ports of the first cylinder group fluidly coupled to an intake of the engine and exhaust ports of the second cylinder group fluidly decoupled from the intake.