Which mechanism controls the amount of fuel injected into a diesel engine cylinder by a unit injector?

The correct answer is that a metering helix inside the pump controls the amount of fuel injected into a diesel engine cylinder by a unit injector. The metering helix is a precision component within the fuel injection pump that regulates the volume of fuel delivered to the injector based on engine operating conditions and demands.

As the engine operates, the position of the metering helix adjusts the flow of fuel by varying the size of the fuel passage. This adjustment ensures that the correct amount of fuel enters the cylinder at the right time to achieve optimal combustion and performance. The design of the metering helix allows it to respond dynamically to changes in engine load and speed, thereby enabling efficient fuel delivery.

This mechanism is essential for maintaining engine efficiency and reducing emissions, making it a critical component in modern diesel engines that utilize unit injectors.