Exam Question
(a) Describe with the aid of sketches a fuel pump capable of variable injection timing.
(b) State why injection timing might need to be changed.
(c) State how injection timing is adjusted while the engine is running.
Class 2 (2nd Engineer)
MEKM
📅 Feb 2021
Reference Answer
(a) Variable Injection Timing (VIT) Fuel Pump:
The VIT fuel pump is designed to adjust both the timing and quantity of fuel injected into the engine. It operates using a plunger that moves up and down in a barrel, driven by a cam. The movement of the plunger controls two valves: the suction valve and the spill valve. These valves are actuated through pivoted levers and push rods.
Injection Start (Suction Valve Control):
When the cam follower is on the cam’s base circle, the suction valve is open. As the cam rotates, the plunger moves upward, causing the suction valve push rod to move downward and close the suction valve. This marks the beginning of fuel injection.
The VIT fuel pump is designed to adjust both the timing and quantity of fuel injected into the engine. It operates using a plunger that moves up and down in a barrel, driven by a cam. The movement of the plunger controls two valves: the suction valve and the spill valve. These valves are actuated through pivoted levers and push rods.
Injection Start (Suction Valve Control):
When the cam follower is on the cam’s base circle, the suction valve is open. As the cam rotates, the plunger moves upward, causing the suction valve push rod to move downward and close the suction valve. This marks the beginning of fuel injection.
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