Here’s a detailed explanation of the Fuel Supply System in a Petrol (Spark Ignition – SI) Engine:
What Is the Fuel Supply System in an SI Engine?
In petrol engines, the fuel supply system ensures proper delivery of air-fuel mixture to the engine’s combustion chamber for ignition via a spark plug. It must maintain the correct air-fuel ratio (usually 14.7:1) for optimal performance, fuel economy, and emission control.
Main Components of Petrol Engine Fuel Supply System:
- Fuel Tank
- Stores petrol.
- Equipped with a cap, vent, and fuel level sensor.
- Fuel Pump
- Delivers petrol from the tank to the engine.
- Mechanical pumps are common in carburetor systems; electric pumps are used in fuel-injected systems.
- Fuel Filter
- Removes dirt, rust, and debris to protect the fuel system.
- Fuel Lines
- Carry fuel from the tank to the carburetor or injector.
- Carburetor or Fuel Injector
- Carburetor: Mixes air and fuel mechanically (older engines).
- Fuel Injector: Delivers precise fuel amounts (modern engines with MPFI or GDI systems).
- Air Filter
- Filters the incoming air before mixing with fuel.
- Throttle Body
- Regulates air intake and controls engine speed.
- Intake Manifold
- Distributes the air-fuel mixture evenly to all cylinders.
- Spark Plug
- Ignites the compressed air-fuel mixture in the combustion chamber.
Working of the Fuel Supply System (SI Engine):
A. In Carbureted System (Conventional)
The carbureted system is a traditional fuel delivery method where air and fuel are mixed mechanically in a device called the carburetor before entering the engine. It relies on engine vacuum and airflow to draw fuel, making it simple and low-cost, but less precise in controlling fuel-air mixture.
- Air enters through the air filter.
- Fuel is pumped from the fuel tank to the carburetor.
- The carburetor mixes fuel and air in the proper ratio.
- The air-fuel mixture flows to the intake manifold, then into the cylinders.
- The spark plug ignites the mixture.
B. In Fuel Injection System (Modern)
- Air is filtered and controlled by the throttle body.
- An ECU-controlled electric pump sends pressurized fuel to the injectors.
- Injectors spray fuel directly into the intake manifold or combustion chamber.
- Sensors monitor engine conditions, and the ECU adjusts fuel delivery accordingly.
🔍 Types of Fuel Supply Systems in Petrol Engines:
| System Type | Key Feature | Common In |
|---|---|---|
| Carburetor | Mechanical mixing of air & fuel | Older cars & bikes |
| Single-point injection (SPI) | One injector for all cylinders | Early fuel-injected cars |
| Multi-point injection (MPFI) | Individual injector per cylinder | Most modern petrol engines |
| Gasoline Direct Injection (GDI) | Injects fuel directly into cylinder | High-efficiency petrol engines |
Also Read: Single point vs Multi point vs Gasoline Direct injection.
Conclusion:
The fuel supply system in petrol engines plays a critical role in engine performance, combustion efficiency, and emissions control. Modern systems favor electronic fuel injection for better control and fuel economy compared to older carburetor-based designs.
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