Class 2 (2nd Engineer) MEKM 📅 Aug 2023

Exam Question

(a) Explain the term Variable Injection Timing (VIT) when applied to fuel pumps and state why a change in timing of fuel injection may be required. (5)

(b) Describe, with the aid of sketches, a VIT fuel pump and explain how the change in timing is achieved whilst the pump is in operation. (5)

(c) Explain how it may be determined that individual fuel pumps are injecting the correct quantity of fuel with the correct timing at a particular pump setting. (6)

Reference Answer

(a) Variable Injection Timing (VIT) Fuel Pump:
Variable injection timing (VIT) is a form of fuel pump control enabling an engine to operate with the designed maximum cylinder firing or combustion pressure from approximately 85% power output to maximum power.
Reasons for Changing Injection Timing
Advancing the injection timing ensures the maximum cylinder pressure (Pmax) is reached at around 85% Maximum Continuous Rating (MCR), improving combustion efficiency and reducing fuel consumption.

Full answer on MeoMock — surveyor-grade reference answers for 7,000+ written exam questions.

View plans Browse library

← Browse more questions

Prepare on Android — MeoMock on Google Play