Introduction to Fuel System

The fuel system supplies a quantity of clean, well-atomized fuel to the engine. Depending on the engine's operating conditions, the fuel is mixed with a certain amount of air to form the combustible mixture. At the same time, the fuel system needs to store a considerable amount of fuel in order to ensure that the vehicle can run smoothly.

1. Working principle

2. Components

    2.1 Fuel tank

    2.2 Fuel level sensor

    2.3 Fuel filter

    2.4 Fuel pressure regulator

    2.5 Fuel rail

    2.6 Injector nozzle

    2.7 Carbon canister

3. Cleaning

1. Working principle

The fuel system takes charge of fuel filling and transportation, ensuring that fuel reaches the engine. It is available for engine operation. It is also responsible for collecting the oil vapour and discharging it outside through filtration.

The principle of absorption and desorption of the evaporation system is that the fuel in the tank produces oil vapour due to changes in ambient temperature.

When the vapour pressure is greater than the set value, the system's two-way valve opens. The oil vapour enters the carbon canister. The activated carbon can absorb the vapour.

When the system's internal pressure is less than the set value, the two-way valve opens, and outside air enters the system through the carbon canister to replenish it.

When the engine is running, the ECU detects the opening condition of the carbon canister purge valve. The valve opens, and fuel vapour enters the engine under negative pressure in the intake manifold to participate in combustion.

2. Components

Take a look at what parts make up a car's fuel system. The fuel tank, fuel pump, fuel level sensor, fuel pipe, fuel filter, fuel pressure regulator, fuel rail, injector nozzle, carbon canister come together. They are collectively known as the fuel system.

2.1 Fuel tank

The function of the fuel pump is to draw petrol from the fuel tank. The pump sends the fuel through the pipes and the filter to the fuel rail. The fuel is atomized by the fuel injector and finally reaches the combustion chamber.

Thanks to the fuel pump, the tank can be placed at the rear of the car, away from the engine and below the engine.

The main form of installing the electric fuel pump for petrol injection engines is in the oil supply line or the fuel tank. The former has a larger layout. It does not require a specially designed tank. It is easy to install and dismantle.

However, the part of the fuel pump suction is long. It is easy to produce air resistance. The working noise is also awful. In addition, it is required that the fuel pump should never leak. This type of pump is less used in new vehicles at present.

The latter one has a simple fuel line. It doesn't make too much noise. The fuel leakage requirements are not very strict. It is the current main trend.

During the engine working, the flow rate of the fuel pump should provide the consumption required to run the engine. It keeps sufficient return flow to ensure stable pressure and adequate cooling of the fuel system.

2.2 Fuel level sensor

The oil level sensor is used to detect the oil level in vehicle fuel tanks. It uses the ferrite magnet to generate the magnetic field and controls the on/off of the reed switch contacts.

It converts the change in the measured level into an electrical signal output and connects to the secondary instrument, thus detecting the level height.

2.3 Fuel filter

The main function of the fuel filter is to filter out the impurities in the fuel. If the filter is too dirty or clogged, the main manifestations are: when refueling the door, the power is sufficient. The acceleration is weak. It's hard to start the car. Sometimes it even takes 2-5 times to get started.

Most engines are now fitted with disposable, non-removable paper filters, with a replacement cycle of 10000 km, or 15000-20000 km if there are few impurities in the gasoline.

The filter is marked with an inlet and outlet arrow. It is not allowed to be installed backwards when replacing it.

2.4 Fuel pressure regulator

The function of the fuel pressure regulator valve is to ensure that the fuel pressure in the vehicle's oil circuit works properly. There is a diaphragm inside the pressure regulator that controls the opening and closing of the pressure valve. When the oil pressure falls below a certain value, the valve closes.

Delcoribo Fuel Pressure Regulators

As the fuel pump increases the pressure in the oil circuit when it increases beyond the prescribed pressure, the diaphragm opens and the over-pressurized fuel flows back to the tank through the return line. The whole process plays a role in reducing the pressure.

2.5 Fuel rail

The fuel rail is a component of the air/fuel subsystem in the electronically controlled fuel injection system. It is a mechanical device mounted on the intake manifold at the fuel injector.

2.6 Injector nozzle

The role of oil injection to the cylinder and the working condition of the injectors are associate with the power of each engine.

Delcoribo Injector Nozzles

Poor fuel leads to poor functional injector nozzle, so that the carbon deposits in the cylinder is severe. Wear and tear of the piston ring accelerates, which causes unstable idling speed, more fuel consumption, weak acceleration, hard starting and excessive emissions.

Therefore, the injector nozzle should be cleaned regularly. The frequence is essential. Not cleaning at all or too often cleaning can both have harmful effects.

The duration of cleaning depends on the car condition and the quality of the fuel that is usually pumped in. Generally speaking, if everything is good, it can be extended to around 40000-60000 km. If there is a slight blockage of the injector nozzle, it has a certain impact on the vehicle.

Sometimes there is such a problem. When you shift into first gear and start, the car shakes a bit. When you shift into high gear and accelerate, the symptom disappears.

Assuming that sensors in the vehicle are working correctly, the throttle has been cleaned, and the circuitry is normal, it is likely that the injector is slightly blocked.

2.7 Carbon canister

When the engine is not running at idle speed, you can hear a specific sound from time to time. Don't panic when you encounter this. The first thing to do is to find the carbon solenoid valve and determine if the sound is from there.

If so, there is no big deal. The carbon solenoid valve will produce an intermittent switching action when the throttle is opened, thus making a sound. This is quiet normal.

When the engine is not running at idle speed, you can hear a specific sound from time to time. Don't panic when you encounter this. 

The first thing to do is to find the carbon solenoid valve and determine if the sound is from there. If so, there is no big deal. The carbon solenoid valve will produce an intermittent switching action when the throttle is opened, thus making a sound. This is quite normal.

3. Cleaning

The regular cleaning of the fuel system is vital for the fuel system. It improves the performance and effectiveness and extends the system's service life.

If the fuel system is not cleaned properly, the engine's power performance will be reduced. It even makes the EFI system work unstably.

The precipitates produced by the combustion will block the needle valve of the injector nozzle, affecting the performance of the precision components in the electronic injection system. It leads to a reduction in power performance.

Furthermore, the engine may idle erratically and stall easily. The fuel consumption increases. Precipitates form carbon deposits at the intake valves. The valve can't close properly, and the pressure drops. In addition, it shortens the service life of the three-way catalytic converter.

There will be some water in the fuel. The specific gravity of water is greater than that of oil. The water will slowly separate out and stay in the bends of the oil circuit or the filter, resulting in a discontinuous oil supply.

When the temperature is very low, the water will condense into ice and cause the oil circuit to become blocked. The engine will then not work.

Therefore, the fuel system must be cleaned regularly. It is also important to note that cleaner is something you should care about. Be sure to choose a good one at first.

Lauritz Carolsfeld        December 10, 2021

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