CHAPTER 2 - PART 2 - ENGINE AUXILIARY SYSTEMS - FUEL SUPPLY SYSTEM

The fuel supply system provides the fuel needed for engine operation and, together with the intake system, helps form the mixture required for combustion. In carburettor engines, the air-fuel mixture, consisting of air and petrol, is formed outside the cylinder, with its formation beginning in the carburettor and continuing during intake.

The fuels used are petrol for spark-ignition engines and diesel fuel for compression-ignition engines.

In engines with petrol injection, the air-petrol mixture is formed in the intake manifold or inside the cylinder.

FUEL SUPPLY SYSTEM OF SPARK-IGNITION (SI) ENGINES

It consists of:

• fuel tank: stores the fuel needed for engine operation;

• petrol pump: supplies the carburettor with fuel drawn from the tank;

• carburettor: mixes petrol with air in the ratio required for engine operation;

• air filter: forms part of the intake system and traps dust and impurities in the air drawn in from outside, preventing them from entering the combustion chamber.

In modern engines, fuel is supplied mainly through injection systems. In spark-ignition engines, the carburettor has largely been replaced by petrol injection. This can be indirect, when the fuel is injected into the intake manifold, or direct, when the fuel is injected directly into the cylinder.

FUEL SUPPLY SYSTEM OF COMPRESSION-IGNITION (CI) ENGINES

It consists of:

• fuel tank: stores the diesel fuel needed for engine operation;
• fuel feed pump: delivers fuel to the injection equipment;

• fuel filters: remove impurities and water from the fuel before it reaches the injection system;
• injection pump: delivers diesel fuel under high pressure through the high-pressure lines to the injectors;

• injectors: ensure fine atomisation and uniform distribution of the fuel in the combustion chamber. In these engines, the injectors allow fuel to be introduced only at the required time, in the quantity determined by the fuel supply system;
• mechanical speed governor: regulates the operation of the injection pump so that the fuel supply matches the engine's operating requirements.

In compression-ignition engines, fuel is supplied through electronically controlled high-pressure diesel injection systems. One example is the common rail system, in which diesel fuel is maintained under pressure in a common rail and delivered to the injectors, which spray it into the cylinders at the required time.