Which fuel injection system features a spring-loaded differential spray needle valve?

The fuel injection system that features a spring-loaded differential spray needle valve is jerk pump injection. This type of injection system utilizes a pump that delivers fuel at high pressure in a controlled manner, optimizing the injection timing and volume for each cylinder. The spring-loaded differential spray needle valve in this system helps improve atomization and ensures that the fuel is injected at the right moment during the engine's cycle, enhancing combustion efficiency and performance.

In jerk pump injection, as the fuel is injected, the differential spring action allows for a precise opening and closing of the nozzle, which assists in optimizing the spray pattern. This is particularly critical in applications where fuel efficiency and emission control are priorities.

The other systems mentioned do not employ this specific design feature. Common-rail injection systems use a single high-pressure rail to supply fuel to all injectors, air injection typically involves mixing air with exhaust for emissions control, and distributor injection systems utilize a single distribution pump to deliver fuel to multiple cylinders without the same needle valve mechanism found in jerk pumps.