In this blog post, I will explain the difference between VIT and Super VIT in an engine. VIT stands for Variable Injection Timing, which is a method of adjusting the fuel injection timing to improve the thermal efficiency and reduce the specific fuel oil consumption of an engine. Super VIT is a type of VIT that has more features and flexibility than conventional VIT.
VIT and Super VIT
VIT works by advancing or retarding the start and end of fuel injection depending on the load condition. By doing so, it maintains a constant maximum cylinder pressure (Pmax) at low loads, which improves combustion and reduces smoke emission. At high loads, it retards the injection timing to avoid excessive peak pressure and knocking.
Super VIT is a type of VIT that is used on some large engines like MAN B&W S-MC, K, L series engines. It has two main advantages over conventional VIT:
– It has an adjustable break point, which is the load point where Pmax has been reached and injection timing has been advanced the most. Above this point, injection timing is gradually retarded back until it reaches its original setting at 100% MCR (maximum continuous rating) load. This helps to optimize combustion over a wider range of loads and reduce NOx emission.
– It has a fuel quality setting (FQS), which is a lever that can adjust the position of the pump barrel relative to the camshaft. This allows changing the amount of fuel injected per stroke without changing the pump index or rack position. This helps to adapt to different fuel qualities and viscosities without affecting injection timing.
To summarize, these two are methods of adjusting fuel injection timing in an engine to improve performance and efficiency. Super VIT has more features than conventional VIT, such as adjustable break point and fuel quality setting.
For SULZER/Wartsila ENGINES
VIT works by controlling the movement of suction and spill valves in the fuel delivery pump. These valves determine when the fuel injection starts and ends for each cylinder. By changing the position of an eccentric shaft that drives these valves, VIT can advance or retard the injection timing.
The VIT actuator is a pneumatic cylinder that receives a signal from a load indicator, which measures the engine load based on governor output lever position. The actuator moves the eccentric shaft according to a predefined curve that matches different load ranges. The VIT actuator also has a mechanical stop that limits its stroke and prevents excessive advance or retard.
The benefits of VIT are:
– Improved combustion efficiency and lower specific fuel oil consumption at part load operation
– Reduced exhaust gas temperature and thermal stress on engine components
– Reduced smoke emission and carbon deposits
– Adaptation to different fuel qualities with poor combustion behavior
VIT is a traditional feature of Wartsila (Sulzer) slow-speed engines, but it can also be found in some medium-speed engines such as Wartsila 16V32 . The VIT settings for each engine type are specified by the manufacturer and should be checked regularly for proper operation.
To maintain VIT performance, marine engineers should follow these tips:
– Check the freeness of mechanical parts such as suction and spill valves, eccentric shaft spring, stop plate and linkage
– Check the correspondence between load indicator values at different positions (setting plate, local maneuvering stand, remote control system)
– Check the actuator stroke when VIT is zero by inserting a distance sleeve between suction valve regulating lever and blocking unit
– Check the clearance and alignment between stop plate and linkage when fitting VIT after maintenance
– Check electrical connections for electronically operated VIT
I hope you found this blog post informative and useful. If you have any questions or comments, please feel free to leave them below.
