370 Diesel Engine Technology Copyright Goodheart-Willcox Co., Inc. As stressed in previous chapters, a diesel engine must be provided with fuel that is properly metered and delivered in the combustion chamber at the proper time. Equally impor- tant, the fuel must be atomized into a controlled spray pat- tern and injected in such a manner that it burns completely without producing excessive black smoke or particulates. Atomization and final fuel delivery is the job of the injection nozzle. Nozzle designs can vary with the type and size of the combustion chamber. This chapter discusses the various types of injector nozzles used in diesel engines. Nozzle Holders All injector nozzles are enclosed in nozzle holders, Figure 18-1. The nozzle holders are mounted in the engine cylinder head. They position the nozzle in the engine cyl- inder, hold the needed spring and pressure adjustments to provide the proper nozzle valve action, and provide a means for conducting fuel to the nozzle and combustion chamber. A copper gasket is installed between the injector and the cylinder head so that the maximum amount of oper- ating heat possible will be transmitted to the engine coolant. Holder Construction A typical holder assembly consists of a body, nozzle spacer, lower spring seat, pressure adjusting spring, spring adjusting spacers, or a screw and a nozzle cap nut, Figure 18-2. The holder body contains a high pressure tubing connection, a high pressure fuel duct, a leak-off duct, and a leak-off connection. The lower end of the body is machined to accept the pressure adjusting spring and spacers. The lower end of the nozzle holder is provided with a precision ground and lapped surface that forms a leak-proof seal with the lapped surface of the nozzle body. The nozzle is secured to the holder by a cap nut. The lower spring seat provides a seat for the pressure adjusting spring and a piloting surface for the nozzle valve stem. The nozzle spacer contains two locating pins that position the nozzle radially to ensure proper spray pattern orientation within the combustion chamber. Both faces of the spacer are lapped to a fine finish to provide a high pres- sure seal between the holder and nozzle body faces. The spacer also acts as a valve stop. Nozzle Fuel Flow Fuel from the high pressure tubing enters the nozzle holder assembly at the upper end and flows down the high pressure duct through the nozzle spacer duct and into the nozzle. A slight amount of fuel leakage will occur past the nozzle valve’s major outside diameter into the adjusting spring chamber. This fuel is used to lubricate the valve spring seat and adjusting spring and then escapes back to the fuel tank through the leak-off duct and connection. Types of Injector Nozzles There are two major types of injector nozzle designs: open nozzles and closed nozzles. In open injector nozzles, there is no valve used to stop the flow of fuel from the nozzle tip. The amount of fuel passing through an open nozzle is completely controlled by the injection pump. Closed injector nozzles are designed with a spring-loaded valve located near the nozzle’s exit orifice. Valve opening and closing is controlled in one of three ways: mechani- cally, hydraulically, or electronically. One advantage of the open nozzle is that it does not easily become clogged with carbon particles or bits of other Injector holders Injector nozzles Figure 18-1. Typical nozzle holder designs. (AMBAC International) Leak-off pipe connection Spring Nozzle holder Nozzle nut Nozzle Orifices Valve seat Annular area of valve Needle valve Spindle Fuel inlet Copper washer Cap nut Return fuel High pressure fuel Low pressure fuel Figure 18-2. Components of a typical injector holder assembly.