Diesel Injectors.... How do they work?

[Doug Rorem]

>>
>>Not quite EFI, but while looking for Injectors, I met a good friend at 
>>NOPI, and he showed me alot of injectors... I noticed that the Diesel ones
>>had Fuel in, and two little ports on the sides.  How do these injectors 
>>know when to fire?
>>
>>                Thor Johnson

Thor,

The injection pump ramps up the fuel pressure very high (roughly 2500 psi)
and the injector 'fires' when it's breaking pressure is reached. For VW diesels
there is a moveable pintle in the nozzle that is spring loaded which determines
the 'breaking' pressure. There are shim washers that are used to adjust the
spring force and thus the pressure for firing. When the right pressure is
reached, the pintle nozzle moves up into the injector body and fuel
sprays out. When the pressure drops, the spring shoves the pintle back
into place which cuts off fuel flow, readying the injector for the next
cycle.

The two ports on the side of a VW injector are for excess fuel flow which goes
back to the fuel tank.


--
Doug Rorem
University of Illinois at Chicago         (312)-996-5439  [voice]
EECS Department  RM 1120                  (312)-413-1065  [fax]
851 S. Morgan Street                      (708)-996-2226  [pager]
Chicago, IL 60607-7053                    rorem at uic.edu