Page 137 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Therefore, when the butterfly is opened by the accelerator pedal, the diaphragm is pulled outward against the
spring pressure by the suction generated by the corresponding vacuum. A governor is a device used to regulate
the speed of engines or machines. There are two main types:
1 Centrifugal governor: Uses rotating weights driven by the engine to control the throttle or fuel supply, adjusting
the engine speed based on centrifugal force.
2 Fly ball governor: Utilizes a linkage system connected to a spinning flywheel. As the speed increases,
centrifugal force causes the fly balls to move outward, which then adjusts the throttle or fuel supply to regulate
the speed.
Fuel Injectors

The function of the fuel injector is to deliver finely atomized fuel under high pressure to the combustion chamber for
the engine. All component parts of the injector are carried in. nozzle holder (10.) The main part of the injector is the
nozzle comprising nozzle body (12) and nozzle valve (11) The nozzle body and needle valve are fabricated from
alloy steel. They are thoroughly machined and have high surface harness necessary for operation in condition of
high temperatures and elevated pressures. The bore in the nozzle body and the nozzle needle valve are lapped
to a close tolerance and are a matched set, so that neither the nozzle body nor the needle valve may be replaced
individually. The needle valve is pressed against a conical seat in the nozzle body by spring (4) acting through
the 212 intermediary of stem 8. The spring pressure is adjusted by adjusting screw (2). The adjusting screw is
screwed in the bottom of the injector spring cap nut which in tum is screwed in the nozzle holder. Lock nut (3) is
used to prevent the adjusting screw from unscrewing spontaneously. The screw is covered by nozzle holder cap
nut (1) provided with a threaded hole to connect the leak-off pipe through which the leak-off fuel (used to lubricate
the nozzle valve) filling the pressure spring and adjusting screw area is returned to the fuel tank or the secondary
fuel filter. In operation, fuel from the injection pump enters pressure chamber (gallery) (15) in the nozzle body
through supply passage (9) and a high-pressure pipe. When the fuel pressure in the pressure chamber becomes
so high that the force acting on the pressure taper of the needle valve from below exceeds the set spring force on
the stem, the needle valve lifts off its seat and comes to rest with its upper shoulder against the face of the nozzle
holder. Fuel is then forced out of the nozzle spray holes into the combustion chamber in a spray pattern which
depends on the type of nozzle used. After the injection of fuel has been ended, the fuel delivery from the injection
pump ceases, the pressure in pressure chamber 15 of the nozzle drops instantly, and the pressure spring snaps
the needle valve onto its seat, preventing unpressurized fuel from leaving the nozzle. The fuel injector is installed
in a brass injector tube, or sleeve, which is fitted in a hole in the cylinder head, and is held in place by a special
clamp Injectors are provided to atomize the fuel into engine cylinder. This is done to achieve complete combustion.
Following types of nozzles are used in engine.
• Single hole type
• Multi hole type
• Long stem type

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CITS : Automotive - Mechanic Diesel - Lesson 31 - 38