Injection Delay-continued

TM 9-2320-312-24-2

Systems Operation Section

The plunger continues moving downward and the

plunger continues to inject fuel into the combustion

chamber. Until the PRIME groove in the plunger

lines up with the PRIME spill port in the barrel, the

plunger continues to inject fuel into the combustion

chamber. When the groove in the plunger aligns

with the spill port, high pressure fuel under the

plunger can flow upward. The high pressure fuel

flows through three holes in the bottom of the

plunger. Then, the high pressure fuel flows out of

the groove of the plunger and the spill port and the

fuel flows back into the fuel supply passage. This

loss of high pressure fuel causes injection pressure

to drop below Valve Closing Pressure (VCP). The

spring force overcomes the hydraulic force of the

reduced injection pressure. When the spring force

overcomes the hydraulic force of the reduced

injection pressure, the check closes and fuel

injection stops. This is the end of the pilot injection

and the start of the short injection delay period.