MERCHANDISING 3C2751 - Caterpillar

Illustration 1 g01009248
Fuel injector (typical example)
(1) Plunger
(2) Pumping chamber
(3) High-pressure fuel passage
(4) Cartridge valve
(5) Low-pressure fuel passage
(6) Needle valve
(7) Valve chamber When the stroke of plunger (1) is at the top, fuel flows through the low-pressure fuel passages in the body. The fuel then flows to the center passage in the plunger and into pumping chamber (2) below the plunger. When the stroke of the plunger is at the bottom, fuel flows through high-pressure fuel passages (3). The fuel flows through open cartridge valve (4) and into low-pressure fuel passages (5). When the cartridge valve is closed or energized, the fuel flow through the cartridge valve is blocked. This blockage causes a buildup in fuel pressure and injection to begin. Injection continues until the cartridge valve is de-energized or open. Fuel is allowed to flow through the cartridge valve. There will then be a drop in pressure and the injection will stop. The plunger continues to force fuel through the open cartridge valve until the stroke of the plunger reaches the bottom. The fuel injector spring returns the plunger to the starting position and the cycle repeats.The start of fuel injection is determined when the cartridge valve is opened or closed by the Electronic Control Module (ECM) via the injector solenoid. The quantity of fuel that is injected is determined when the cartridge valve is opened or closed.During the fuel injection stroke, the fuel passes from the pumping chamber into the fuel injector nozzle. The nozzle has a needle valve (6) that is spring loaded. Fuel flows through the fuel passage around the needle valve to valve chamber (7). In the valve chamber, the fuel pressure lifts the needle valve away from the seat. The fuel can now flow through the orifices in the tip into the combustion chamber.The bottom of the fuel injector protrudes for a short distance below the cylinder head into the combustion chamber. The fuel injector tip has several small orifices that are equally spaced around the outside diameter. The orifices spray fuel into the combustion chamber.