The engine arrangement (1) comprises: an internal combustion engine (2) and an exhaust pipe (3) capable of collecting exhaust gases from said engine; an injection device (7) designed to inject an exhaust treatment fluid inside the exhaust pipe (3), and an after-treatment device (4) located downstream from the injection device (7), for at least partially removing undesired components from the exhaust gases; a bypass line (8) branching from the exhaust pipe (3) upstream from the injection device (7), and capable of carrying a sub-flow (F1 ) of the exhaust gases towards a supply device (9) which is arranged at the after- treatment device inlet and which is designed to direct said sub-flow (F1) towards a sector (10) of the after-treatment device (4), while the exhaust gases flowing in the exhaust pipe (3) towards the after-treatment device (4) pass through the complementary portion (11 ) of the after-treatment device (4); a heater (18) designed to heat the exhaust gases sub- flow (F1); and an additional injection device (16) designed to inject an exhaust treatment fluid inside the bypass line (8).