FILTER ELEMENT AS-OIL 3997921 - Caterpillar

PRe-Injection MEtering (PRIME)
The fuel system on the 3126B diesel engine has a unique feature that is called PRe-Injection MEtering (PRIME). PRe-Injection MEtering (PRIME) is a feature that offers a significant benefit in lower emissions. Also, the PRIME system 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.PRIME injectors produce a small pilot injection that is followed by a brief delay. The brief delay gives the pilot injection the time that is required to start burning. The main injection follows the pilot injection and the main injection is delivered into the flame front that was established by the pilot injection. The main injection is immediately ignited. The main injection burns smoothly and the main injection burns completely. This complete combustion significantly reduces particulate emission (soot) and NOx. This complete combustion also reduces combustion noise from the engine up to 50 percent. This reduction of combustion noise from the engine results in noticeably quieter engine operation. The PRIME operation is described in the following information.Injection Delay
Illustration 13 g00295363
HEUI Injector Delay (1) Upper poppet seat ( closed). (2) Lower poppet seat (open). (A) Drain (atmosphere). (B) Fuel supply pressure. (C) Actuation oil pressure. (D) Moving parts. (E) Injection pressure. (F) Fuel flow. (G) Mechanical movement.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