What occurs when the pressure of fuel surpasses the pressure of the spring in a hydraulic injector?

When the pressure of fuel surpasses the pressure exerted by the spring in a hydraulic injector, the nozzle needle moves upward. This upward movement is crucial for the operation of the injector as it allows fuel to be injected into the combustion chamber of an engine.

In a hydraulic injector system, the spring serves to maintain the nozzle needle in a closed position during low-pressure conditions. When fuel is pumped through the injector and its pressure rises above the spring's resistance, it forces the needle to lift against the spring's tension. This lifting action creates an opening in the nozzle, enabling the pressurized fuel to be sprayed into the combustion chamber for mixing with air and subsequent ignition.

Therefore, the correct answer highlights the fundamental function of hydraulic injectors in controlling fuel delivery based on pressure differentials, which are crucial for engine performance and efficiency.