Chapter 18 Injection Nozzles 385 Copyright Goodheart-Willcox Co., Inc. through which the pintle extends. Hole size and angle affect the spray pattern and spray density. Delay pintle nozzles reduce the amount of fuel injected in the early stages of injection. This limits the amount of fuel in the chamber when combustion begins, which helps reduce preignition and knocking. CAV Pentaux nozzles are designed with an auxiliary spray hole to assist in easy starting in cold weather conditions. Injection nozzles are precision instruments that are very sensitive to dirt and water, which can wear and/ or corrode nozzle surfaces. Proper precautions must be taken when removing and installing injection nozzles to prevent the entrance of dirt and contaminants into the fuel system. All nozzle cleaning operations must be per- formed using nonabrasive cleaning tools, such as brass wire brushes. Injector operation can be tested using a pop tester. Checks include valve open/close pressure, valve seat sealing test, back pressure test, chatter test, and spray pattern checks. Complete disassembly, cleaning, inspec- tion, and reassembly of injection nozzles requires special equipment and training. Most of this work is done in spe- cialized fuel injection service shops. The mounting bore and surrounding area must be thoroughly cleaned prior to reinstalling the nozzle on the engine. Once the nozzle is remounted and its fuel lines reconnected, air must be bled from the fuel lines. The pencil fuel injection nozzle is a multi-hole, dif- ferential pressure nozzle that is much smaller than other nozzle types. The spray-tip body and inlet fitting are per- manently attached to the nozzle body. The needle valve and the spindle are also one unit. The valve is guided by the spray tip body and by the closely fitted valve guide. The lower spring seat rests against the needle valve while the upper spring seat rests against the pressure-adjusting screw. The lift adjustment screw threads into the pressure adjusting screw. The pencil nozzle operates in the same way as hole- and pintle-type nozzles, but its needle valve opens and closes more rapidly. When tested, a good pencil injector will give off a distinct chatter. Review Questions—Chapter 18 Answer the following questions using the information provided in this chapter. 1. True or False? Open injector nozzles are the most popular nozzle type in use today. 2. Name the two types of closed injector nozzles in use today. 3. _______ nozzles are used in small-bore, high-speed engines. (A) Hole (B) Pintle (C) Open (D) None of the above. 4. Direct injection, open combustion chamber diesel engines, such as those used in heavy-duty truck appli- cations mainly use _______ injector nozzles. (A) hole (B) pintle throttling (C) open (D) None of the above. 5. The pressure required to open a nozzle delivery valve is _______ than the pressure required to keep it open. 6. In a fuel injector nozzle, the fuel sac under the seat must be as _______ as practical to help reduce emis- sion levels. 7. The main advantage of a CAV Pentaux pintle nozzle is _______. (A) higher injection pressures (B) easier starting in cold weather (C) narrow spray cone for deep penetration (D) long service life 8. Which of the following will have an effect on the shape of the injected fuel spray cone? (A) Nozzle hole size. (B) Spray angle. (C) Injection pressure. (D) All of the above. 9. Name at least five basic engine checks that should be made before turning attention to the injectors. 10. Which of the following is true concerning pencil injection nozzles? (A) The spray-tip body and inlet fitting are perma- nently attached to the nozzle body. (B) Its needle valve opens and closes much faster than a standard nozzle valve. (C) A capped pencil nozzle has no return fuel line. (D) All of the above. 1. Fuel injector nozzle holders _______. (A) position the nozzle in the engine cylinder (B) contain the needed spring and pressure adjust- ments to provide the proper nozzle valve action (C) provide a means for conducting fuel to the nozzle and combustion chamber of the engine (D) All of the above. 2. In a fuel injection nozzle, the slight amount of fuel leakage occurring past the nozzle valves into the adjusting spring chamber is _______. (A) used for cooling (B) used to lubricate the valve spring seat and adjusting spring (C) unavoidable but causes no harm (D) a sign of a defective nozzle ASE-Type Questions