An injection nozzle assembly serves to position the nozzle accurately in the engine cylinder. An injection nozzle assembly will contain the necessary spring and pressure adjustment means to provide for the proper action of the nozzle valve. An injection nozzle assembly will also provide a means by which fuel can be conducted the the nozzle and the combustion chamber of the engine. Although manufacturers produce a wide variety of nozzles to meet the requirements of several different combustion systems and engine sizes, there are essentially two basic groups of injection nozzles: the pintle nozzles and the hole nozzles.

Refer to the cutaway sectional view of a Bosch injection nozzle assembly in figure 9-20. Notice the details of the nozzle holder and the pintle-type nozzle. The high-pressure fuel from the injection pump enters the nozzle holder body through a metal-edge strainer. From the strainer, the fuel goes through a drilled fuel passage that extends to the bottom of the nozzle holder body. The nozzle, with its spray tip, is held against the bottom of the nozzle holder by the cap nut. A groove in the top of the nozzle forms a circular passage for the fuel between the nozzle and the holder. (Refer to fig. 9-21.)

Several vertical ducts (shown in detail in fig. 9-20) carry the fuel from the circular passage to the fuel cavity, near the bottom of the nozzle. The nozzle valve cuts in sharply to a narrower diameter in the fuel cavity, providing a surface against which the high-pressure fuel in the fuel cavity can act to raise the valve from its seat in the spray tip. When the valve is raised from its seat, the fuel sprays out to the combustion chamber through

Figure 9-20.-Sectional view of a Bosch injection pintle-type nozzle assembly.

a ring of small holes (hole nozzle), or around the pintle and out through the single hole (pintle nozzle).

The valve has a narrow stem that projects into the central bore of the nozzle holder where it bears against the bottom of the spindle. The spindle is held down by the pressure-adjusting spring. Whenever the upward force of the high-pressure fuel acting on the needle valve exceeds the downward force of the spring, the valve can rise. The moment the spring force is greater, the valve will snap back to its seat. The spring tension is regulated by a pressure-adjusting screw or shims.

Regardless of the close-lapped fit of the valve, some fuel will leak past the valve and rise through the central bore of the nozzle holder. This fuel lubricates the moving parts and carries away heat from the injector. The bypassed fuel then drams off through the fuel dram connection to a drip tank. There is a bleeder screw that can serve to bypass fuel to the nozzle, sending the fuel directly to the fuel drain.

The pintle nozzle and the hole nozzle are com-pared in views A and B of figure 9-21. Refer to figure 9-21 as you read the following descriptions.

Figure 9-21.-Pintle Nozzle and hole nozzle.