A four-stroke reciprocating piston internal combustion engine is disclosed. The engine includes an even number of cylinders grouped into a first half and a second half. An exhaust gas turbocharger has a first turbine inlet and a second turbine inlet. Each of the cylinders has an intake duct with an intake opening, a first exhaust duct with a first exhaust opening, and a second exhaust duct with a second exhaust opening. The first half of cylinders is connected via the respective first exhaust ducts to the first turbine inlet and is connected via the second exhaust ducts to the second turbine inlet. The second half of cylinders is connected via the respective first exhaust ducts to the second turbine inlet and is connected via the respective second exhaust ducts to the first turbine inlet. The respective second exhaust openings have a larger diameter than the respective first exhaust openings.

Methods and systems are provided for operating an engine in a two-valve diagonal blow-through mode during which a majority of blow-through is directed via a first intake valve positioned diagonally across a first exhaust valve in order to increase a distance of flow path from the intake valve to the exhaust valve.

A variable valve device for an internal combustion engine is equipped with a variable valve mechanism capable of changing the working angle of an intake valve while holding the maximum lift amount of the intake valve constant. The variable valve device retards the timing for closing the intake valve as the load of the internal combustion engine rises, and enlarges the working angle, while holding the timing for opening the intake valve constant. Operating characteristics of the intake valve are provided in accordance with the load of the internal combustion engine.

A method for injecting nitrogen into an internal combustion engine cylinder includes moving a piston back and forth in a cylinder and injecting pure nitrogen into a combustion chamber during the compression stroke. The method includes injecting the fuel and nitrogen into different regions to create a stratified gas environment, igniting the fuel, and releasing exhaust emissions. An engine system for injecting nitrogen into an internal combustion engine includes a cylinder, a first intake line, one or more nitrogen injectors, and a fuel injector. An engine system for injecting nitrogen into an internal combustion engine includes a cylinder, an intake line, and a multi-nozzle injector with a fuel nozzle and a nitrogen nozzle.