Pre-Injection Metering (PRIME)

TM 9-2320-312-24-2

Systems Operation Section

The PRIME feature produces a small pilot injection

When the ECM activates the unit injector, the ECM

that is followed by a brief delay. The brief delay

sends a current to the unit injector solenoid. The

gives the pilot injection the time that is required

current causes the solenoid to produce a strong

to start burning. The main injection follows the

magnetic field which creates a pull on the armature.

pilot injection and the main injection is delivered

The armature is mechanically connected to the

into the flame front that was established by the

poppet valve by a screw. The magnetic pull of

pilot injection. The main injection is immediately

the solenoid overcomes the spring tension that is

ignited. The main injection burns smoothly and the

holding the poppet valve closed. When the poppet

main injection burns completely. This complete

valve opens, the poppet moves away from the lower

combustion significantly reduces particulate

poppet seat.

emission (soot) and NOx. This complete combustion

also reduces combustion noise from the engine

When the poppet valve opens, the upper poppet

up to 50 percent. This reduction of combustion

seat (1) blocks the path to the drain and the lower

noise from the engine results in noticeably quieter

poppet seat (2) opens the poppet chamber to

engine operation. The actual operation of PRIME is

incoming high pressure actuation oil. High pressure

described in the following information.

oil flows around the poppet. The high pressure

oil flows through a passage onto the top of the

intensifier piston. High pressure oil acts on the top

of the intensifier piston. The piston and the plunger

are pushed down by the high pressure oil. The

downward movement of the plunger pressurizes

the fuel in the plunger cavity and nozzle assembly.

When the pressure reaches Valve Opening Pressure

(VOP) of approximately 28 MPa (4000 psi), the

check lifts up from the seat in the tip. When the

check lifts up from the seat in the tip, injection

begins.

Pre-Injection Metering (PRIME)

The 3126B and 3126E diesel engine's fuel

system has a unique feature that is called PRIME.

PRe-Injection Metering (PRIME) is a feature that

offers a significant benefit in lower emissions.

Also, PRIME offers a significant benefit in reducing

combustion noise. While other fuel systems deliver

a single large quantity of fuel into the combustion

chamber, PRIME injectors break the delivery into two

separate quantities. The first quantity is a small pilot

injection which is followed by a short delay. Then,

the injector delivers a large main injection. The pilot

injection is not intended to produce power. The pilot

injection is intended to establish a flame front. The

pilot injection will help the larger main injection burn

more completely and the pilot injection will help the

larger main injection burn in a controlled manner.

Under certain engine operating conditions, when

fuel is delivered in one large injection, the fuel tends

to explode rather than burn in a controlled manner.

This results in engine knock. When fuel explodes

rather than burns in a controlled manner, engine

knock and excess NOx emissions result.