A fuel jet pump, also known as an ejector pump or Venturi pump, is a passive device that uses the kinetic energy of a high-velocity fluid stream to move a secondary fluid without any moving parts. It's commonly found within fuel tanks to transfer fuel from one section to another, ensuring a consistent supply to the primary electric fuel pump.
How a Fuel Jet Pump Works
The operation of a fuel jet pump is based on the Venturi effect and Bernoulli's principle. Here's a breakdown of the process:
- Primary Fuel Supply: Fuel from a main electric booster pump, which is already under pressure, is directed to the jet pump.
- Nozzle Acceleration: This high-pressure fuel is channeled through a specially designed nozzle. As the fuel passes through the constricted opening of the nozzle, its velocity significantly increases, while its static pressure drops dramatically.
- Entrainment and Suction: The high-velocity fuel jet exiting the nozzle creates a low-pressure zone (a vacuum or suction effect) in the surrounding area. This pressure differential draws in the secondary fuel from the tank's isolated compartment.
- Mixing and Pressure Recovery: The primary and secondary fuel streams mix in a mixing chamber.
- Diffusion: The combined fuel then flows into a diffuser, which is a gradually expanding section. In the diffuser, the velocity of the fuel decreases, and its static pressure increases, allowing it to be effectively moved towards the main fuel pump or another part of the tank.
This entire process occurs seamlessly, often with the jet pump installed directly on the wall or base of the fuel tank, leveraging the output of the main fuel pump to perform additional fuel transfer tasks.
Key Components
A fuel jet pump consists of three primary components:
- Nozzle: Accelerates the primary fluid (fuel from the booster pump) into a high-velocity jet, creating a low-pressure area.
- Mixing Chamber (Suction Chamber): Where the high-velocity primary fluid entrains and mixes with the secondary fluid.
- Diffuser: Converts the kinetic energy of the mixed fluid back into pressure energy, allowing it to be moved effectively.
Advantages and Applications
Fuel jet pumps offer several benefits, making them crucial in modern fuel systems:
- No Moving Parts: This translates to exceptional reliability, long lifespan, and reduced maintenance compared to mechanical pumps.
- Simplicity: Their design is straightforward, minimizing potential points of failure.
- Cost-Effective: They are generally less expensive to manufacture than electric pumps.
- Space Efficiency: Their compact design allows for installation in tight spaces within fuel tanks.
Common Applications:
- Saddle Fuel Tanks: Many vehicles feature saddle-shaped fuel tanks that wrap around drive shafts or exhaust systems. A single electric fuel pump typically sits in one half of the tank. A fuel jet pump is essential here to scavenge fuel from the other half and transfer it to the primary pump's side, preventing fuel starvation.
- Aircraft Fuel Systems: Used to transfer fuel between different tanks or compartments, ensuring proper fuel balance and supply to engine-driven pumps.
- Marine Vessels: Similar to automotive applications, they help manage fuel across complex tank geometries.
By continuously transferring fuel, jet pumps ensure that the main electric fuel pump always has an adequate supply, regardless of fuel level or vehicle inclination, contributing significantly to engine performance and reliability.
