An engine system includes an engine housing having a cylinder block and a cylinder head. An intake opening and an exhaust opening and an igniter opening are formed in a fire deck surface of the cylinder head. A plurality of always-open fuel admission ports are fluidly connected to a combustion chamber and arranged in at least one of the cylinder block or the cylinder head. The always-open fuel admission ports convey a gaseous fuel such as a gaseous hydrogen fuel, a gaseous hydrocarbon fuel, or still others, to the combustion chamber.