The present invention is directed to an internal combustion engine (100) having at least one cylinder (10), preferably a large vessel engine with at least one cylinder (10) having an inner diameter (11) of at least 200mm, and to a method for operating an internal combustion engine. A piston (12) is provided in said cylinder (10) for reciprocating between a bottom dead center and a top dead center. The internal combustion engine (100) has a scavenging port (13) formed in said cylinder (10) for supplying scavenging gas into a combustion chamber (14) that is a space enclosed by said cylinder (10) and an upper surface (15) of said piston (12). The internal combustion engine (100) has an exhaust port (16) formed in said cylinder (10) for exhausting gas out of said combustion chamber (14), the exhaust port (16) comprises an exhaust valve (17).
The internal combustion engine comprises at least one dosing unit (18, 18.1, 18.2, 18.3, 18.4) for ejecting a reducing agent, preferably liquid ammonia, into said combustion chamber (14), preferably at least one dosing unit (18) for each cylinder (10). The internal combustion engine (100) comprises a control unit (20) for controlling the dosing unit (18, 18.1, 18.2, 18.3, 18.4), adapted for ejecting a first amount (31) of the reducing agent into said combustion chamber (14) during expansion stroke during a time interval (32) that falls in a time window (33) from when the exhaust valve (17) opens until before supply of said scavenging gas through said scavenging port (13) into said combustion chamber (14) is started.