VIT

VIT stands for Variable Injection Timing. It is a mechanism used in marine fuel pumps to control the timing of fuel injection in an engine.
 
 
VIT in fuel pump
 
 
The VIT system allows the fuel pump to adjust the timing of fuel injection based on various factors such as engine speed, load, and temperature. This helps to optimize fuel efficiency and performance in the engine. 
 
In marine fuel pumps, the VIT system is typically controlled by an electronic control module (ECM) that receives input from various sensors in the engine and adjusts the fuel injection timing accordingly. The VIT system can be used to fine-tune the fuel-to-air ratio in the engine, which can help to improve combustion efficiency and reduce emissions.
 

The Super VIT is available in both a mechanical and an electronic version. In the electronic version, an I/P converter supplies the pilot air pressure to the individual servo cylinders, instead of the pilot valve activated by the fuel rack used in the mechanical version.

 

The I/P converter receives its pilot signal from the governor system. The advantage of the electronic version is that the break-point is calculated from the actual conditions, why the ambient conditions are taken into account. The engine load is calculated from the engine speed and the fuel index, while the compression pressure is calculated from the scavenging air pressure. Based on these calculations the governor calculates the output to the I/P converter.

 

 

With the CRIS the HP pump delivers fuel to the rail which is common to all cylinders. Each injector is actuated in sequence by the ECU as a function of the crankshaft angle. The injector opens when energized and closes when de-energized.

 

The amount of fuel per cycle is determined by the time differential and the in-system pressure. The actual in-system pressure is transmitted to the control unit via a pressure sensor and the rail pressure is regulated by the ECU via the actuator in the fuel supply to the HP pump. With this system, the injector incorporates several functions.

 

The nozzle needle is relieved by a solenoid valve and thus opened by the fuel pressure. The amount of fuel injected during the ignition delay period is regulated by the nozzle opening speed.

 

With this servo-assisted injector, the opening and closing characteristics can be adjusted individually and affected extremely precisely. It is capable of extremely high reaction speeds for controlling minimum fuel quantities during idle operation or pilot injection.

For Advanced Read, check out:

Marine Engine Components

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