Automotive Fuel Supply System

Automotive fuel supply system

An automotive fuel supply system is a series of components connected to supply fuel (petrol or diesel) from the fuel tank to the fuel injector OR carburetor.

Automotive fuel supply system consists of following components,

  1. Fuel tank
  2. Fuel pump (primary & secondary)
  3. Fuel filter
  4. Fuel lines (hose or pipe for supply and return line)
  5. Fuel injector 
  6. Carburetor (outdated technology, but still used in two-wheeler)
  7. Fuel gauge/indicator
Fuel system components
Fuel System

Types of the Fuel supply system,

1.Gravity feed fuel supply system

2.Pressure feed fuel supply system

Gravity System: Gravity fuel system used in two-wheeler and portable petrol (gasoline)/diesel engine generator. In two-wheeler, the fuel flows from the tank to the carburetor/fuel injector due to gravity.

Pump System: In this system fuel flows from the fuel tank to the fuel injector by a fuel pump. Pressure system applications are used in cars, trucks, and buses. Unlike a gravity system, fuel cannot be moved from the fuel tank to the fuel injector by gravity, so the fuel pump is essential

Please refer following block diagram of the fuel system.

Fuel supply pump system

Safety requirements in the fuel system:

Various standards available to conduct the safety test of the automotive fuel system.

  • As per safety standards, fuel lines shall not be routed inside the passenger cabin. 
  • The safe distance must be maintained between the fuel line and exhaust manifold (including exhaust pipe)
  • Precaution should be taken during the design phase for the mounting of the fuel tank to avoid damage to the fuel tank in case of a front collision or back end collision. As a safety system, fuel tanks are mounted between the front and rear wheel, so it can be protected during front-end collision or rear-end collision.
  • The fuel tank should withstand internal pressure (generated due to fuel vaporization)
  • A safety vent is required to control the overfilling of fuel.
  • Fuel lines should be covered by a protective enclosure to avoid damage, abrasion to fuel lines due to obstacles such a stone, speed bump during the driving condition.
  • The fuel line should withstand mechanical, thermal stresses. Fuel line material shouldn’t react with the fuel.
  • The fuel tank should withstand mechanical and thermal stress.
  • Fire-resistance test, high-temperature test, mechanical strength test conducted to prove the safety of the fuel system

Fuel tank:

Fuel tank act as a reservoir of fuel. In commercial vehicles, metallic fuel tanks are used. In light vehicles, plastic fuel tanks are used. Plastic fuel tanks are made by High-density polyethylene (HDPE). Plastic fuel tanks are made by an injection blow molding process in any complex shape.

Plastic fuel tanks are seamless tanks and light in weight compared to the metallic fuel tank. Heatshield must be provided if the exhaust pipe is routing closer to the plastic fuel tank.

Mounting of fuel tank

Mounting of fuel tank requires 2 to 3 steel strips. These steel strip further joined to the chassis by using a screw. Fuel tanks mounting joints are considered a safety joint in automotive and these joints are tightened by a programmed DC nut runner to avoid loose fitment of the fuel tank or missing fastener.

Fluid surging effect inside the fuel tank:

Sudden braking and turning of the vehicle creates a fluid surging effect inside the fuel tank. The fuel surge effect is nothing but a wave generation inside a closed tank. Fluid surging imbalances vehicle dynamics. To avoid fluid surging in-side the fuel tank and to maintain better vehicle dynamics, fuel tanks are equipped with baffles / vertical panels. Baffles inside the fuel tank generate a small compartment inside the fuel tank, which helps to eliminate the surging effect at great extent.

Fuel tank equipped with following child-parts.

  1. Lid/cap: For fueling and to maintain atmospheric pressure inside the fuel tank.
  2. Fuel level sensor: To sense fuel level inside the tank.
  3. Baffle plates: To avoid the fluid surging effect.
  4. Drain plug: To remove dirt/residue/impurities from the fuel tank.
  5. Vapor recovery system: To avoid evaporation of fuel.
  6. Fuel filter: Supply of clean fuel by eliminating residue/sediments inside the fuel
Types of fuel pump

Fuel lines

In the automotive fuel system flexible fuel line (hose) and rigid fuel lines (tubes) are used. Fuel lines are routed from the fuel tank to the engine compartment with the enclosure to avoid the abrasion of fuel lines. In-car/SUV, fluid channel provided so the fuel line is passed in chassis. This design avoids the risk of fuel line damage/abrasion or pinching of the fuel line if the car under body collides with a speed bump. Grommets are used to avoid the abrasion of fuel lines with the car metallic body.

Types of fuel lines:

1.Synthetic rubber tubes

2.Reinforced rubber hose

3.Plastic fuel lines

Safety Requirements of Fuel lines:

SAE J30 specifies requirements for fuel line testing. 

  1. Fuel resistance test
  2. Change in length test
  3. Vacuum collapse test
  4. Burst test
  5. Cold flexibility test.

For detailed information about fuel line safety and test requirements please refer SAEJ30 standard.

Fuel Filters:

Primary function of the fuel system is to supply clean fuel to the fuel system by eliminating dust, contamination, sediments from fuel. Failure of fuel filter leads to a chock-up of the fuel injection system. If the fuel filter is blocked with impurities/dirt, it will stop functioning and there won’t be any fuel supply to the fuel pump. The poor performance of the fuel filter leads to the poor performance of the engine.

Performance test of fuel filters

  1. Material compatibility test
  2. Flow resistance test
  3. Filter capacity
  4. Meeting environmental condition

Fuel Pump:

The function of the fuel pump is to supply fuel from the fuel tank to the fuel injection system.

Types of fuel pump:

1.Electrical fuel pump

2.Mechanical fuel pump

An electrical fuel pump is used in a modern ECU controlled vehicle. A mechanical fuel pump system is outdated technology, but it is still used in a light commercial vehicle as the cost of a mechanical pump system is less. 

Mechanical Fuel Pump Vs Electrical Fuel Pump

Mechanical Fuel PumpElectrical Fuel Pump
Mechanical fuel system operated by engine camshaft / crankshaft. The mechanical fuel system operates after engine cranking only.The electrical fuel pump is actuated by a vehicle battery power. It can start functioning before the engine starts.
The mechanical fuel system mounted on the engine as it requires a mechanical drive to operate.The electrical fuel pump is not mounted on the engine block as it does not require a mechanical system to operate.
The fuel supply rate of the mechanical fuel pump cannot be controlled by the (ECU) engine control unit.Efficient in moderating fuel supply rate to engine speed and load as electrical fuel pump function can be controlled by an engine control unit (ECU)
If the mechanical pump fails, it’s a greater risk of fuel leakage/seepage inside the engine compartment. This may cause a fire in the engine compartment.No risk of fuel leakage inside the engine compartment as the electrical fuel pump is not mounted inside the engine compartment.
Less costly as compared to an electric fuel pump.Comparatively to the mechanical fuel pump cost of the electrical pump is high.
The mechanical fuel system can operate as long as engine cranking is possible.Failure of the electrical system or battery discharge may lead to electrical pump failure.
The mechanical fuel pump can operate in a push start.The electrical fuel pump does not work in the push start method as sufficient power will not be generated by the battery system.

References: SAE J30 standard.

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