How is the amount of fuel delivered by a unit injector controlled?

The amount of fuel delivered by a unit injector is primarily controlled by the rack position. In fuel-injection systems that utilize a unit injector, the rack, which is a component typically connected to the governor, adjusts the position of the injector. When the rack moves, it changes the quantity of fuel that the injector delivers to the combustion chamber.

In essence, the rack position allows the engine management system to dictate how much fuel should be injected based on various operational parameters, such as load and speed. This variable control is crucial for achieving optimal engine performance, efficiency, and emissions.

While camshaft timing, main spring, and engine speed play roles in the overall function of the injector system, they do not directly determine the volume of fuel being injected as effectively as the rack position does. The camshaft influences timing, while the main spring provides the necessary force for opening and closing the injector, and engine speed can affect the rate of fuel delivery but doesn't directly adjust the amount injected on its own.