Purging method and system 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 fuel injection 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 inner wall (12), a plunger (13) configured to reciprocate within the pump barrel (10) and guided by the barrel inner wall (12), and a first groove (3 8) formed in the barrel inner wall (12) at a first position with respect to the longitudinal direction and always covered by the reciprocating plunger (13). A purging system (125) may be provided to be connected to the first groove (38). The purging system (125) may be configured to supply a purging fluid through the first groove (38).