384 Diesel Engine Technology Copyright Goodheart-Willcox Co., Inc. Summary Fuel atomization and final delivery is the job of the injection nozzle. Nozzle designs vary with the type and size of the combustion chamber. All injector nozzles are enclosed in nozzle holders. The nozzle holders are mounted in the engine cylinder head. Direct injection, open combustion chamber diesel engines, such as those used in heavy-duty truck applica- tions, mainly use long-stem hole injector nozzles. A typical hole nozzle consists of a valve and body fitted together to form a mated assembly. Fuel under high pressure gener- ated by the fuel injection pump flows through the fuel duct in the body and enters the pressure chamber. When the fuel pressure exerts sufficient force on the nozzle valve, the valve is lifted off its seat, allowing fuel to enter the sac beneath the seat. It is directed through the spray holes into the combustion chamber. The fuel is atomized as it exits the spray holes and enters the combustion chamber. A hole nozzle has one or more straight, round spray holes or orifices. Pintle nozzles are used in small-bore, high-speed engines. Pintle nozzles are also used in engines having pre- combustion, divided, air cell, or energy-cell combustion chambers. With a pintle nozzle, only a small amount of fuel is injected at the beginning of injection. The fuel flow rate then increases progressively as the valve lifts higher off its seat. A pintle nozzle generally opens at a lower fuel pressure than a hole nozzle. Pintle nozzles have thin shanks or pins that extend into the nozzle opening. These pins help create the proper spray cone pattern needed for injection. Pintle nozzle bodies have a single hole opening Spray Pattern Test Close the pressure gauge and pump the tester at 30 strokes per minute. The spray pattern should be similar to those illustrated earlier in this chapter for hole nozzles. Chatter Test Perform a chatter test, pumping the tester handle at a rate of one stroke per second. There should be a distinct chatter. Lack of chatter may indicate a bent or sticking nozzle. If readjustment does not solve the problem, replace the nozzle. Seat Condition Check Check valve seat leakage by raising the pressure to 400–500 psi (2758–3448 kPa) below opening pressure and observing for drips and leaks at the nozzle. Check back leakage by raising the nozzle tip up, Figure 18-35. Raise the fuel pressure to 1500 psi (10,343 kPa) and count the number of drips from the return in 30 seconds. There should be 3–10 drips. If back leakage is excessive, the nozzle should be replaced. Nozzle Assembly Assemble a new compression and carbon dam seal as shown in Figure 18-36. A newly installed carbon dam does not return to size immediately, but soaking the nozzle in warm calibrating oil will speed the pro- cess, if needed. Cap the nozzle inlet and tip until the nozzle is installed on the engine. On capped nozzles, replace the nozzle cap seal, install the cap, and tighten to specified torque. Pencil Nozzle Installation To reinstall the pencil nozzle, first clean the cylinder bore with a bore cleaning tool and clean and check the sealing surface of the cylinder head. Install the nozzles in the cylinder head using a slight turning motion to set them in position. Do not use lubricant. Attach the holding clamps and torque them to specifications. Finally, install the fuel leak-off lines using new plastic boots on the noz- zles to prevent leaking. (Horizontal plane) Figure 18-35. To check back leakage, the nozzle tip must be higher than the return line. (Stanadyne Diesel Systems) Install new compression seal Seal tool Carbon dam seal Figure 18-36. Assembling injector seat. A—Installing compres- sion seal. B—Installing carbon dam. (Stanadyne Diesel Systems)