Fuel injection system of compression ignition internal combustion engine

A fuel injection system of a compression ignition internal combustion engine provided with a fuel injection valve that injects fuel directly into a cylinder of the internal combustion engine, in which sub fuel injection is executed multiple times by the fuel injection valve in addition to main fuel injection at a time earlier than the main fuel injection, wherein the system comprises:

• a number of times changing unit which changes the number of times of execution of sub fuel injection in one combustion cycle based on an operation range within which the operation state of said internal combustion engine falls so that the lower the engine load of said internal combustion engine is, and the lower the number of engine revolutions of said internal combustion engine is, the more the number of times of execution of sub fuel injection in one combustion cycle is increased;
• a common rail that supplies fuel to said fuel injection valve;
• and
• a pressure changing unit which changes the pressure in said common rail in accordance with the number of times of execution of sub fuel injection in one combustion cycle,
• wherein the lower the atmospheric pressure is, the lower the temperature of cooling water of said internal combustion engine is, or the lower the temperature of intake air of said internal combustion engine is, the more an operation range in which the number of times of execution of sub fuel injection in one combustion cycle is large is expanded to higher loads and higher revolutions, and
• wherein, if the number of times of execution of sub fuel injection in one combustion cycle is to be decreased by said number of times changing unit, then said pressure changing unit starts changing the pressure in said common rail, and said number of times changing unit starts the decrease in the number of times of execution of sub fuel injection only after a specific period has elapsed,
• wherein said specific period is determined to correspond to a response delay period beginning with the start of the changing of the pressure in said common rail and ending when said pressure changing unit completes the changing of the pressure in said common rail to a target value corresponding to the decreased number of times of execution of sub fuel injection.