Operation of the HEUI Fuel Injector

TM 9-2320-312-24-2

Systems Operation Section

When the injection pressure increases to

approximately 28 MPa (4000 psi), the hydraulic

force that is pushing on check (3) becomes greater

than the spring force that is holding the check

down. When the spring force is overcome by the

hydraulic force, the check moves away from tip (4).

When the check moves away from the tip, the check

is in the open position. The amount of pressure that

is required to open the check is called the Valve

Opening Pressure (VOP). The fuel flows out of tip

orifice holes (5) in the end of the tip and the fuel

flows into the combustion chamber. The check

remains open and fuel continues to flow out of the

tip until fuel injection pressure drops below 28 MPa

(4000 psi). When the pressure drops, the check

closes and fuel injection is stopped. The amount of

pressure that allows the check to close is called the

Valve Closing Pressure (VCP).

Note: Valve Opening Pressures (VOP) and Valve

Closing Pressures (VCP) vary among applications

and horsepower ratings in order to meet exhaust

emission standards. The above values were used

as illustrations only.

The inlet fill check ball (1) unseats during upward

travel of the plunger in order to allow the plunger

cavity to refill. The inlet fill check ball seats during

the downward stroke of the plunger and the inlet

fill check ball seals during the downward stroke of

the plunger. The inlet fill check ball seals during the

downward stroke of the plunger in order to prevent

fuel injection pressure leakage into the fuel supply.

Operation of the HEUI Fuel Injector

There are five stages of injection with the HEUI

injector:

Pre-injection

Pilot injection

Delay

Main injection

End of injection