Influence on Injection and Combustion Phenomena by Elimination of Hole Nozzle Sac Volume

For the reduction of unburned hydrocarbon emission from DI diesel engines nozzle sac volume is reduced and, in some cases, eliminated by covering the orifice with a valve.

Studies on the sacless nozzle, however, clarified that it seriously influences the injection phenomena :

1. i.
   The state of the fuel spray is different at each spray hole and at each needle lift.
2. ii.
   Facilitates the combustion gas blow-back into the nozzle.

The following are elucidated through this study :

1. i.
   Irregular state of spray bases on flow line at the space between seat and needle different for each orifice and for each needle lift.
2. ii.
   Gas blow-back occurs when needle bouncing and cylinder gas oscillation take place at the same time.