Reduction of Idle Combustion Noise with the Groove Needle of Injection Nozzle in a D.I. Diesel Engine

The two-spring injection nozzle used in D.I. diesel engines is known to be effective in reducing idle combustion noise by suppressing initial fuel injection rate. An increased injection pressure, however, decreases the noise reduction, because the pressure drop at the initial stage of needle lift (pre-lift) is not enough to lower the initial injection rate at a needle lift of 0.06 mm which is the minimum pre-lift from the viewpoint of production precision and reliability for a DLLA-S-type nozzle. For this reason, the author has proposed a new type of injection nozzle equipped with a groove needle which reduces the level of combustion noise to that of a two-spring nozzle with a smaller needle lift. Experiments revealed that the groove can increase the pressure drop between the upper part of the needle seat and nozzle sac, and reduce combustion noise at an idling condition with almost the same level of engine output and exhaust emissions as the engine equipped a two-spring nozzle with the minimum pre-lift.