The present invention relates to an internal combustion engine arrangement (100) for a vehicle (1), said internal combustion engine arrangement (100) comprising a combustion cylinder (106) housing a reciprocating combustion piston, and an expansion cylinder (110) housing a reciprocating expansion piston, said expansion cylinder (110) being arranged in downstream fluid communication with the combustion cylinder (106) for receiving combustion gases exhausted from the combustion cylinder (106), wherein the internal combustion engine arrangement (100) further comprises a pressure tank (112) arranged in fluid communication with the expansion cylinder (110), wherein the internal combustion engine arrangement (100) is further arranged to be operated in a first operating mode in which compressed gas generated in the expansion cylinder (110) is delivered to the pressure tank (112), and a second operating mode in which compressed gas contained in the pressure tank (112) is delivered from the pressure tank (112) to the expansion cylinder (110).