Spray openings, or orifices, are from 0.006 inch up to about 0.033 inch in di-ameter, and their number may vary from 3 to as many as 18 for large bore engines. Regardless of design, all nozzles and tips function to direct the fuel into the cylinder in a pattern that will bring about the most efficient combustion. Obviously, the slightest defect in nozzles and tips will have an adverse effect on engine operation.

UNIT FUEL INJECTOR SYSTEM

Unlike the design of the other two fuel injection systems, the unit injector provides each cylinder with its own high-pressure pump. The unit injector design eliminates the need for a remotely located high-pressure pump and high-pressure external fuel lines, such as those used in the systems we have covered in the preceding sections. The unit fuel injector (UFI) is complete with pumping and timing element, fuel control, and injection valve spray tip assembly to control the quantity, rate, and timing of fuel delivery. The UFI is used on all General Motors engines; therefore, there are various models available to meet the needs of the engines. Our discussion will cover the two most commonly used types: (1) the crown valve and (2) the needle valve injector.

The crown valve injector is shown in figure 9-22. This type of injector was placed in service in 1953 and is still in use within the Navy. In 1962, the needle valve injector incorporating a new tip design was introduced (fig. 9-23). The needle valve injector provides for improved economy and emissions by increased pop pressure (2300 to 3300 psi for the needle valve injector compared with 450 to 850 psi for the crown valve injector) and a more precise method of fuel control than the crown valve type of unit injector. Compare the spray tip assembly in the crown valve unit injector in figure 9-22 with the spray tip assembly of the needle valve unit injector in figure 9-23.