Methods and systems are provided for providing secondary air to an exhaust system during catalyst warm-up. In one example, a method may include, responsive to a cold start of an engine: operating the engine with a number of unfired cylinders and a remaining number of fired cylinders each engine cycle, and adjusting exhaust mixing by adjusting an exhaust valve parameter of at least one unfired cylinder of the number of unfired cylinders. In this way, the unfired cylinders may provide the secondary air as well as increased mixing of the secondary air with burned exhaust gas from fired cylinders, thus increasing exotherm production in the exhaust system to increase a temperature of the catalyst.

An exhaust passage structure of an internal combustion includes a first merging passage, a second merging passage, and a third merging passage connecting a third gathering portion in which the exhaust gas flowing through the first merging passage and the exhaust gas flowing through the second merging passage gather and a turbine of a turbocharger. The first merging passage and the second merging passage have respective narrowed portions in which passage cross-sectional areas are minimized. When a total value of passage cross-sectional areas of inlets of exhaust ports in one cylinder is set as a reference passage cross-sectional area A, and the passage cross-sectional areas of the narrowed portions of the first merging passage and the second merging passage are set as narrowed cross-sectional areas B, the exhaust passage structure is configured such that the relationship of 0.5≤(B/A)≤1 is established.

Methods and systems are provided for reducing emissions during an engine cold start. In one example, a method may include, during emission control device heating, injecting heated air into an exhaust runner of each cylinder of the engine during an exhaust stroke of the corresponding cylinder, after a blowdown exhaust pulse. In this way, an amount of hydrocarbons in feedgas provided to the emission control device prior to the emission control device reaching its light-off temperature may be reduced.

Methods and systems are provided for reducing emissions during an engine cold start. In one example, a method may include, during emission control device heating, injecting heated air into an exhaust runner of each cylinder of the engine during an exhaust stroke of the corresponding cylinder, after a blowdown exhaust pulse. In this way, an amount of hydrocarbons in feedgas provided to the emission control device prior to the emission control device reaching its light-off temperature may be reduced.

A method performed by a control unit (11) for controlling exhaust valves (1A-6A, 1B-6B) of cylinders (1-6) in an internal combustion engine (10) is provided. The method comprise controlling (410) a number of first exhaust valves (1A-3A) for a first set of cylinders (1-3) to transfer exhaust gas to a turbine (8)) during part of an exhaust phase (Δt.sub.1) of the first set of cylinders (1-3) via a first exhaust manifold (12). Also, the method comprises controlling (420) a number of second exhaust valves (1B-3B) for the first set of cylinders (1-3) to transfer exhaust gas to an exhaust gas recirculation, EGR, conduit (9)) during part of the exhaust phase (Δt.sub.1) of the first set of cylinders (1-3) via a second exhaust manifold (7). The method further comprises controlling (430) a number of first exhaust valves (4A-6A) for a second set of cylinders (4-6) to transfer exhaust gas to the turbine (8) during part of an exhaust phase (Δt.sub.2) of the second set of cylinders (4-6) via the first exhaust manifold (12). Furthermore, the method comprises controlling (440) a number of second exhaust valves (4B-6B) for the second set of cylinders (4-6) to transfer exhaust gas to the EGR conduit (9) during a part of the exhaust phase (Δt.sub.2) of the second set of cylinders (4-6) via the second exhaust manifold (7). Here, the exhaust phase (Δt.sub.1) of the first set of cylinders (1-3) is separated in time from the exhaust phase (Δt.sub.2) of the second set of cylinders (4-6). A control unit (11), a computer program, a carrier, an internal combustion engine and a vehicle is also provided.

Methods and systems are provided for improving turbocharger response in a boosted engine. In one example, a current turbocharger performance may be monitored, if meeting and operating in an optimum region for efficiency (e.g., on compressor and/or turbine maps), engine may be operated with a steady state exhaust valve opening (EVO) timing in an optimum position based on engine mapping (e.g., engine pumping work). Otherwise, the EVO timing may be advanced (opening earlier) to release more energy into the exhaust or retarded to release less, to move turbocharger to desired performance. By adjusting EVO timing to achieve desired turbocharger response and performance, faster response is achieved.

Methods and systems are provided for increasing EGR delivered to an engine. In one example, a method may include determining an EVO timing set point and an external EGR setpoint in parallel, based on an inverse model. The EVO timing may be adjusted based on a combination of the EVO timing setpoint and an EGR cylinder balancing feedback loop, thereby varying internal EGR to the engine to supplement external EGR.

A method of operating a gaseous fuel internal combustion engine comprises performing at least one measurement relating to the combustion of a mixture of gaseous fuel and air in a combustion chamber of an associated cylinder in a combustion cycle. At least one combustion parameter, for example, a start of combustion, is determined based on the at least one measurement. When the combustion parameter differs from a desired combustion parameter, an ignition device associated with the cylinder is controlled based on the comparison in order to control the combustion in the current combustion cycle.

A system includes an engine with a plurality of pistons housed in respective ones of a plurality of cylinders, an air intake system provides air to the plurality of cylinders through respective ones of a plurality of intake valves, an exhaust system to release exhaust gas from the plurality of cylinders through one of a plurality of exhaust valves, and a controller coupled to a sensor to control a switching tappet for compression release braking. Alternatively to a tappet, the system includes a roller finger follower controlling an opening and closing timing of exhaust valves, the roller finger follower has an inner roller follower arm adjacent an outer sliding follower, and a controller that in response to an engine braking request locks the inner roller follower arm with the outer sliding follower to contact a second cam lobe and open the exhaust valve during a compression stroke of the cylinder.

A compression-release brake system for operating an exhaust valve of an engine during an engine braking operation. The compression-release brake system comprises a self-contained compression brake control module (CBCM) operatively coupled to the exhaust valve for controlling a lift and a phase angle thereof. The CBCM includes a casing defining an actuator cavity, a actuation piston disposed outside the casing so as to define an actuation piston cavity between the casing and the actuation piston, and a check valve provided between the actuation piston cavity and a compression brake actuator disposed in the actuator cavity. The actuation piston reciprocates relative to the casing. The compression brake actuator includes an actuator element and a biasing spring. The actuator element selectively engages the check valve when deactivated so as to unlock the actuation piston cavity and disengages from the check valve when activated so as to lock the actuation piston cavity.