A - Fuel control rod

B - Fulcrum lever

C - Shaft spring plate

D - Operating shaft spring

E - Operating shaft

F - Operating lever

Figure 5-37. - Governor - sectional view.

Types of Nozzles

Bosch nozzles are inward opening with a multiple orifice and hydraulically operated nozzle valve. The two models of this nozzle in use are the American Bosch and Robert Bosch. They may be easily identified by either the length of the nozzle tip holding nut or the nozzle drilling code on the smaller diameter of the nozzle valve body. The American Bosch nozzle nut is 3 inches long, and the nozzle tip has a hand-printed drilling code. The Robert Bosch nozzle nut is 2 inches long, and the nozzle tip has a machined-etched drilling code. Component parts, although similar, are not interchangeable between the two nozzles.

Nozzle Operation

The pressurized fuel from the injection pump enters the top of the nozzle body and flows through a passage in the body and nozzle spring retainer. An annular groove in the top face of the nozzle valve body fills with fuel, and two passages in the nozzle valve body direct fuel around the nozzle valve. When the fuel in the pressure chamber reaches a predetermined pressure, the spring force (adjusted by shims) is overcome and injection occurs. Atomized fuel sprays from the orifice holes in the nozzle tip, as the nozzle valve is opened inward by pressurized fuel. When injection ends, spring pressure snaps the valve in its seat. During each injection, a small quantity of high-pressurized fuel passes between the nozzle valve stem and the nozzle valve body to lubricate and to cool the nozzle valve. A manifold that connects to all of the nozzles returns this fuel to the tank.

Fuel Density Compensator

The multifuel engine operates on a variety of fuels that have a broad range of viscosities and heat values. These variations in the fuels affect engine output. Because it is unacceptable for the power output of the engine to vary with fuel changes, the multifuel engine is fitted with a device known as a fuel density compensator (fig. 5-38). 'The fuel density compensator is a device that serves to vary the quantity of fuel injected to the engine by regulating the full-load stop of the fuel pump. The characteristics of the fuels show that their heat values decrease almost inversely proportional to their viscosities. The fuel density compensator uses viscosity as the indicator for regulating fuel flow. Its operation is as follows:

The fuel enters the compensator through the fuel pressure regulator where the fuel pressure is regulated to a constant 20 psi regardless of engine speed and load range.

The pressure-regulated fuel then passes through a series of two orifices. The two orifices, by offering greatly different resistances to flow, form a system that is sensitive to viscosity changes. The first orifice is annular, formed by the clearance between the servo piston and its cylinder. This orifice is sensitive to viscosity. The second orifice is formed by an adjustable needle valve and is not viscosity sensitive. 5-43