Purging method and system with scraper or wiper ring for preventing formation of deposits inside fuel pump

The present disclosure refers to a fuel injection system (100) configured to supply fuel as, e.g., heavy fuel oil to injection nozzles (105) of a large internal combustion engine (5). The system may comprise a fuel injection pump (110) configured to measure fuel as, e.g., heavy fuel oil into correct amounts for injection, building up a high pressure, and delivering it to at least one injection nozzle (110) of the large internal combustion engine (5) at the proper time. The fuel injection pump (110) may include a pump barrel (10) extending along a longitudinal direction and having a barrel wall (12), and a plunger (13) configured to reciprocate within the pump barrel (10) and guided by the barrel wall (12). At least one scraper ring (210; 220) may be attached to one of the plunger (13) and the barrel inner wall (12) and configured to slide along the other of the plunger (13) and the barrel inner wall (12).