Exam Question
(a) With the help of simple diagran, explain Variable Injection Timing (VIT). (8)
(b) Explain with suitable diagram, start and end of VIT points. (4)
(c) Explain with graph Variation of P(Max) with VIT position. (4)
Class 4 (4th Engineer)
MEKM
📅 May 2023
Reference Answer
### (a) Explanation of Variable Injection Timing (VIT)
**1. Definition and Purpose:**
Variable Injection Timing (VIT) is a system fitted to marine diesel engine fuel injection pumps to automatically alter the start of fuel injection with respect to the engine load. It is distinct from the governor/fuel rack, which primarily controls the *end* of injection (i.e., the quantity of fuel). The primary purposes of VIT are:
* **To Optimize Thermal Efficiency:** By controlling the timing of injection, the maximum combustion pressure (Pmax) can be optimized across the engine's load range. This leads to a significant reduction in Specific Fuel Oil Consumption (SFOC), particularly in the 40-85% load range.
**1. Definition and Purpose:**
Variable Injection Timing (VIT) is a system fitted to marine diesel engine fuel injection pumps to automatically alter the start of fuel injection with respect to the engine load. It is distinct from the governor/fuel rack, which primarily controls the *end* of injection (i.e., the quantity of fuel). The primary purposes of VIT are:
* **To Optimize Thermal Efficiency:** By controlling the timing of injection, the maximum combustion pressure (Pmax) can be optimized across the engine's load range. This leads to a significant reduction in Specific Fuel Oil Consumption (SFOC), particularly in the 40-85% load range.
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