Methods and systems are provided for increasing engine power while reducing vehicle emissions and engine system degradation. In one example, a method may include, responsive to an engine load reaching a threshold load, increasing engine torque by increasing an amount of boost without providing exhaust gas recirculation (EGR), and, responsive to the engine torque reaching a first threshold torque, increasing the engine torque by increasing an EGR rate over a plurality of engine cycles while further increasing the amount of boost. In this way, cooling effects from the EGR enable engine air flow, and thus engine power, to be increased while engine vibrations and heat-related exhaust component degradation are decreased.

An electronic control unit performs a cylinder-by-cylinder correction of a fuel injection amount to cause differences among air-fuel ratios of air-fuel mixture burned in multiple cylinders. In a case in which the cylinder-by-cylinder correction of the fuel injection amount results in a cylinder in which combustion is performed at an air-fuel ratio richer than an output air-fuel ratio, the output air-fuel ratio being an air-fuel ratio at which combustion torque is maximized, the electronic control unit performs a cylinder-by-cylinder correction of ignition timing such that the ignition timing of the cylinder in which combustion is performed at the air-fuel ratio richer than the output air-fuel ratio becomes more advanced than the ignition timing of the other cylinders.

Methods and systems are provided for increasing engine power via partial engine enrichment and exhaust gas recirculation. In one example, a method may include enriching a first set of engine cylinders, enleaning a second set of the engine cylinders, and operating a third set of the engine cylinders at stoichiometry, exhaust gas from all of the engine cylinders producing a stoichiometric mixture at a downstream emission control device, and providing exhaust gas recirculation (EGR) to an intake passage of the engine from the first set of cylinders. In this way, cooling effects from the partial enrichment and the EGR enable engine air flow, and thus engine power, to be increased while an efficiency of the emission control device is maintained, thereby decreasing vehicle emissions.

Methods and systems are provided for improving efficiency of an exhaust gas after treatment system of a vehicle. In one example, a first group of engine cylinders is operated with a rich air-fuel ratio continuously while a second group of engine cylinders is operated with a lean air-fuel ratio continuously. The rich and lean exhaust gases from the two groups of engine cylinders may be oxidized within an exhaust gas after treatment system to improve catalyst efficiency.

Methods and systems are provided for cycle-to-cycle torque reductions under exhaust component temperature constraints. In one example, a method may include, responsive to a torque reduction request, introducing a lambda split between two sets of cylinders over a plurality of engine cycles while maintaining an average of stoichiometry between the two sets of cylinders, and, responsive to reaching a lambda split threshold, introducing differentially delayed ignition timing in both sets of cylinders. In this way, fast torque reduction may be provided while maintaining a globally stoichiometric air-fuel ratio, thereby decreasing vehicle emissions, and reducing heat-related degradation to exhaust components.

Methods and systems are provided for operating an engine to diagnose and compensate for cylinder imbalance in an engine. In one example, a method may include diagnosing a torque imbalance in a multi-cylinder engine by operating the engine at a lean air-fuel ratio (AFR) while an amount of ammonia stored in an selective catalytic reduction (SCR) system is greater than a threshold amount and a temperature of the engine is greater than a threshold temperature; and responsive to the diagnosed torque imbalance, adjusting fueling and spark timing for each cylinder, the adjustments based on an AFR offset of each cylinder determined while adjusting the lean AFR.

Methods, devices, controllers, and algorithms are described for operating an internal combustion engine wherein at least some firing opportunities utilize low temperature gasoline combustion (LTGC). Other firing opportunities may be skipped or utilize some other type of combustion, such as spark ignition. The nature of any particular firing opportunity is dynamically determined during engine operation, often on a firing opportunity by firing opportunity basis. Firings that utilize LTGC produce little, if any, nitrous oxides in the exhaust stream and thus, in some implementations, may require no aftertreatment system to remove them from the exhaust stream.

Systems and methods for operating an engine that includes a compression ratio linkage for adjusting engine compression ratio are described. The systems and methods provide different ways of diagnosing the presence or absence of engine misfire in response to engine operating regions that may be more or less prone to torsional engine crankshaft vibration. In one example, engine misfire may be determined responsive to force applied to an engine compression ratio changing linkage.

The present invention relates generally to techniques for improving fuel efficiency of a vehicle powered by an internal combustion engine capable of operating at various displacement levels. An autonomous driving unit or cruise controller selects when possible an engine torque output that corresponds to a fuel efficient displacement level. The resultant vehicle speed profile and NVH level is acceptable to vehicle occupants.

One embodiment is a system comprising an engine including a dedicated EGR cylinder configured to provide EGR to the engine via an EGR loop, a non-dedicated cylinder, a plurality of injectors, an ignition system including a plurality of spark plugs, an intake throttle, and an electronic control system. The electronic control system is configured to control combustion during transient operation of the engine by determining one or more combustion control parameters compensating for variation of one or more of inert matter, unburned air and unburned fuel in EGR output by the dedicated EGR cylinder during transient operation of the engine, and an effect of the EGR loop on inert matter, unburned air and unburned fuel provided to the plurality of cylinders, and controlling operation of at least one of the throttle, the ignition system and the plurality of injectors in response to at least one of the one or more combustion control parameters.