Question

Explain How fuel system components works:

Booster pump-

Jet Pump-

Surge tank-

Crossfeed valve-

Jettison valve-

Capcitance fuel gauge-

Answer 1

1 ) BOOSTER PUMP:

A booster pump is a machine which will increase the pressure of a fluid.

They may be used with liquids or gases, but the construction details will vary depending on the fluid.

A simpler mechanism which often has only a single stage of compression, and is used to increase pressure of a fluid already above ambient pressure. Two-stage boosters are also made.

Booster pumps are usually piston or plunger type compressors. A single-acting, single-stage booster is the simplest configuration, and comprises a cylinder, designed to withstand the operating pressures, with a piston which is driven back and forth inside the cylinder. The cylinder head is fitted with supply and discharge ports, to which the supply and discharge hoses or pipes are connected, with a non-return valve on each, constraining flow in one direction from supply to discharge.

When the booster is inactive, and the piston is stationary, gas will flow from the inlet hose, through the inlet valve into the space between the cylinder head and the piston. If the pressure in the outlet hose is lower, it will then flow out and to whatever the outlet hose is connected to. This flow will stop when the pressure is equalised, taking valve opening pressures into account.

Once the flow has stopped, the booster is started, and as the piston withdraws along the cylinder, increasing the volume between the cylinder head and the piston crown, the pressure in the cylinder will drop, and gas will flow in from the inlet port. On the return cycle, the piston moves toward the cylinder head, decreasing the volume of the space and compressing the gas until the pressure is sufficient to overcome the pressure in the outlet line and the opening pressure of the outlet valve. At that point, the gas will flow out of the cylinder via the outlet valve and port.

There will always be some compressed gas remaining in the cylinder and cylinder head spaces at the top of the stroke. The gas in this "dead space" will expand during the next induction stroke, and only after it has dropped below the supply gas pressure, more supply gas will flow into the cylinder. The ratio of the volume of the cylinder space with the piston fully withdrawn, to the dead space, is the "compression ratio" of the booster, also termed "boost ratio" in this context. Efficiency of the booster is related to the compression ratio, and gas will only be transferred while the pressure ratio between supply and discharge gas is less than the boost ratio, and delivery rate will drop as the inlet to delivery pressure ratio increases.

Delivery rate starts at very close to swept volume when there is no pressure difference, and drops steadily until there is no effective transfer when the pressure ratio reaches the maximum boost ratio.

Compression of gas will cause a rise in temperature. The heat is mostly carried out by the compressed gas, but the booster components will also be heated by contact with the hot gas. Some boosters are cooled by water jackets or external fins to increase convectional cooling by the ambient air, but smaller models may have no special cooling facilities at all. Cooling arrangements will improve efficiency, but will cost more to manufacture.

Boosters to be used with oxygen must be made from oxygen-compatible materials, and use oxygen-compatible lubricants to avoid fire.

2 ) Jet Pump :

A fuel system has a jet pump assembly that fills a fuel reservoir for providing a reliable source of fuel to an electric motor fuel pump located in a fuel tank for a combustion engine.

The electric fuel pump preferably delivers fuel at a controlled pressure to a series of fuel injectors of the engine.

A small portion of the fuel exiting the electric fuel pump is diverted to the jet pump assembly that aspirates fuel from the fuel tank and into the reservoir. A biased normally closed pressure responsive valve prevents fuel flow to the jet pump when the electric fuel pump is running under impaired conditions, thus providing all the fuel to the combustion engine typically during cold engine start conditions.

3 ) Surge tank:

The surge tank is utilized in automotive applications to ensure that the inlet to the fuel pump is never starved for fuel.

It is usually only seen in racing or custom car applications, especially in vehicles that will be sustaining high lateral acceleration loads for extended periods of time.

By using a Fuel Surge Tank / Swirl Pot, ensure that your engine always gets the amount of fuel that´s needed for high power output in demanding conditions e.g. drifting, drag racing and track days. In conditions were your fuel system will be sustaining high lateral acceleration load for an extended period of time.
A Fuel Surge Tank / Swirl Pot ensures that the fuel pumps constantly receive the same access to fuel, regardless of the action of g-forces in constant or variable direction.

By using the flow in your fuel system the surge tank will be constantly filled with fuel. The lift-fuel pump will provide fuel from your fuel tank or fuel cell while the excess fuel returned from the Fuel Pressure Regulator is circulated back into the surge tank. These two flows generate a constant supply of fuel under any conditions, even if the fuel delivery from the fuel tank or fuel cell is reduced due to starvation during low fuel level or extreme conditions.

4 ) Crossfeed Valve:

The crossfeed valve is used to temporarily connect the two sides of the system. This system allows the shortest route for the fuel and keeps the systems separate, so a leak on one side cannot drain the entire system. The crossfeed valve is generally kept shut for this reason.

The fuel system in aircraft generally includes a left and right tank within the corresponding wings. Each tank generally provides fuel to the engines on that wing.

To keep the plane balanced, both wing tanks should have about the same amount of fuel. However, for various reasons, they could become unbalanced. The crossfeed valve allows fuel to flow from the tank with too much fuel to the tank with less fuel.

The purpose of the cross feed valve or cross feed circuit in the airplanes is to separate the fuels in different tanks, especially in the wings (both left and right wings and fuselage) so that one tank will not affect another in terms of leakage.

The other purpose is for the emergency use. If left fuel pump encounters a problem, the right fuel pump will pump fuel from right tank and supply fuel to both engine one and two, through the crossfeed that is automatically opened. Vice versa to right fuel pump.

5 ) Jettison Valve:

fuel jettison is a procedure used by aircraft in certain emergency situations before a return to the airport shortly after takeoff, or before landing short of its intended destination (emergency landing) to reduce the aircraft's weight.

The fuel jettison system allows jettison from all fuel tanks. Override/jettison pumps in main tanks 2 and 3 and the center wing tank pump fuel overboard through the jettison nozzle valves.

Fuel jettison is initiated by rotating the fuel jettison selector to A or B. When a jettison control system is selected, the fuel temperature indication on EICAS is replaced with the fuel to remain quantity indication. The jettison manifold and jettison time display on the fuel synoptic. Rotating the Fuel To Remain selector decreases or increases the fuel to remain quantity.

Pushing either fuel jettison nozzle valve switch ON activates all override/jettison and transfer/jettison pumps in the tanks containing fuel (pump switches must be ON) and opens the required jettison and transfer/jettison valves. The related jettison nozzle valve also opens. The jettison time is initially estimated using preprogrammed rates. The system begins updating the estimate based on actual fuel quantity rate of change ninety seconds after jettison begins.

Jettison terminates when total fuel quantity decreases to the fuel to remain quantity. The fuel to remain quantity indication changes color from magenta to white and flashes for five seconds. The jettison control system deactivates all operating override/jettison and transfer/jettison pumps. The related FUEL OVRD pump EICAS messages display until the Fuel Jettison selector is OFF.

6 ) Capcitance fuel gauge:

In automobile engineering a fuel gauge is an instrument used to indicate the amount of fuel in a fuel tank.

As used in vehicles, the gauge consists of two parts:

• The sensing unit - in the tank
  • The indicator - on the dashboard The sensing unit usually uses a float connected to a potentiometer, typically printed ink design in a modern automobile. As the tank empties, the float drops and slides a moving contact along the resistor, increasing its resistance. when the resistance is at a certain point, it will also turn on a "low fuel" light on some vehicles.   Meanwhile, the indicator unit (usually mounted on the dashboard) is measuring and displaying the amount of electric current flowing through the sending unit. When the tank level is high and maximum current is flowing, the needle points to "F" indicating a full tank. When the tank is empty and the least current is flowing, the needle points to "E" indicating an empty tank.