The injection rate is the ratio of the changes in the fuel quantity that is injected successively from the nozzle within a given unit of time.
As the injection pressure increases, the injection rate increases accordingly. The increase in injection rate leads to an increase in the volume of the air-fuel mixture that is created between the start of injection until ignition (the ignition lag period). Because this mixture is subsequently combusted at once, it creates noise (diesel knock) and NOx. For this reason, it is necessary to appropriately control the injection rate by maintaining a low injection rate at the beginning of injection and supplying a sufficient quantity after the ignition. To meet this need, two-spring nozzles have been adopted and a pilot injection system has recently been developed.
