The illustrated device operates directly by ______.

The illustrated device operates directly by fuel oil pressure because this indicates that the mechanism is designed to utilize the pressure generated by the fuel as a primary means of operation. Fuel oil pressure is commonly associated with fuel injectors in engines, where it serves as the driving force to atomize and inject fuel into the combustion chamber. This method allows for precise control over the fuel delivery, which is crucial for optimal engine performance and efficiency.

Utilizing fuel oil pressure enables the injector to function effectively without needing additional mechanical systems, such as rocker arms or cam assemblies, which are often associated with different types of mechanical movements in engines. By relying on the pressure of the fuel itself, the device can achieve a more direct and efficient response to the engine’s needs. This design is particularly advantageous in modern engines that prioritize performance and efficiency, as fuel pressure can be closely regulated to optimize combustion characteristics.