Fuel Supply System In Petrol Engine: Types & Factors

The fuel supply system in SI engines or petrol engines helps deliver optimum fuel and air to the combustion chamber for power generation. It consists of several components such as the fuel tank, fuel pump, fuel filters, fuel lines, fuel injectors, carburettor, etc. All these parts work together and ensure sufficient fuel reaches the engine. Here’s a list of the parts of a petrol engine fuel system:

Fuel tank: The journey of fuel supply begins from the fuel tank which is the container where fuel is stored. The tank’s capacity ensures your car travels a certain distance without refuelling. The fuel tank is usually installed at the rear.

Fuel pump: Next comes the fuel pump. It is usually placed inside or near the fuel tank. Its main function is to pump the fuel from the fuel tank to the fuel injectors. It creates optimum pressure so fuel injectors release sufficient fuel under different conditions. Fuel pumps can be mechanical or electrical.

Fuel filter: The fuel supply system also ensures the fuel is free from contaminants before it reaches the engine. This is done through the fuel filter. A fuel filter cleans the fuel so no dirt or contaminants damage the engine. It is located between the fuel tank and the pump.

Fuel lines: Fuel lines connect all the components of a fuel supply system. They connect the fuel tank to the injector and injectors to the engine. Fuel lines help maintain flow for a steady supply of fuel.

Fuel injector: This device injects or sprays an optimum amount of fuel and air into the engine for proper combustion. It consists of a valve with a nozzle.

Carburettor: It is found in older cars with internal combustion engines. A carburettor mixes fuel and air in the correct ratio for combustion and ignition.

Fuel gauge: This is a dial on a car’s dashboard that informs you about the fuel quantity in the tank. Fuel gauges in older cars didn't show the correct fuel amount in the tank. However modern gauges provide accurate information about fuel quantity.

Fuel pressure regulator: This crucial device maintains optimum pressure in a vehicle’s engine.

Emission vapour control system: This component plays an essential role in preventing petrol vapours from discharging into the vehicle's surrounding air. Poor functioning of this component can cause bad odour inside the car.

Vehicle manufacturers use different systems to supply the fuel to the engine from the tank. These include the gravity system, pump system, pressure system and fuel injection system. While the first three work with a carburettor, the fuel injection system involves an injector to supply fuel. Let’s discuss each in detail.

Gravity system

This system is installed in smaller vehicles like bikes, quads and entry-level two-wheelers. The fuel tank is placed at the highest position in the system to supply the fuel to the carburettor by gravity. Since the gravity system does not require pumps or additional components it is cheaper to manufacture and maintain. However, it is more rigid since the fuel tank needs to be placed over the carburettor.

Pump system

This system uses a steel pipe to feed fuel to the pump and then to the carburettor float chamber. The fuel pump can be mechanical or electrical. Mechanical pumps are driven by the engine camshaft. Modern vehicles have electric fuel pumps. They provide placement flexibility and prevent vapour locks. This system is suitable for all vehicle types, including buses and trucks. However, fuel pump installation makes it expensive.

Pressure system

This system involves an airtight or pressure-sealed fuel tank. It uses a separate air pump or engine exhaust to create pressure inside the tank using air to deliver the fuel to the carburettor. It requires priming through a hand pump. The pressure system provides more control over the fuel supply than the gravity system. Also, the tank can be installed anywhere in the vehicle. However, the possibility of pressure leaks is a disadvantage of this system.

Fuel injection system

Present-day cars use this fuel supply system. The fuel is atomised by an air injector nozzle and released into the air stream. There is a separate fuel injector for each cylinder. This ensures fuel is delivered in a controlled and precise manner under different load and speed conditions. The fuel injection system is more efficient than the carburettor system. It warms up and starts the engine quickly. However, installing a fuel injection in a petrol engine can be expensive. There is also a possibility of petrol backflow.

Fuel quality can have an impact on the fuel supply system. The following are the factors that determine fuel quality:

Volatility: It is how readily a fuel evaporates.

Ignition quality: It means how easily a fuel can burn in a vehicle’s combustion chamber. Petrol’s ignition quality is usually determined using the octane number.

Calorific value: It is the amount of heat energy produced upon complete combustion of a fuel’s unit mass.

Here are the signs that indicate something is wrong with the fuel supply system:

• Difficulty in starting the car

• Sputtering

• Noise from the tank

• Slow acceleration

• Stalling while driving

• Loss of power due to stress

• Excessive smoke from the engine

• Fuel odour

• Poor fuel efficiency

• Increased fuel consumption

• Engine overheating

• Poor emissions

The performance and efficiency of SI (spark-ignition) engines depend on the proper functioning of the engine fuel system. A faulty system may not allow you to drive your vehicle properly. It may also release poor emissions and harm the environment. Hence, ensuring the well-being of the fuel supply system is important for a smooth driving experience and environmental protection.

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What is the main difference between a mechanical and an electrical pump?

A mechanical pump uses several moving parts to extract fuel from the tank. On the other hand, an electrical pump relies on electrical power and a computer to deliver the fuel to the engine. Also, mechanical pumps are positioned at the side of the car engine while electrical pumps are located above the fuel tank.

What is the full form of SI engine?

SI stands for Spark Ignition. It is an internal combustion engine and usually a petrol engine. In this, the combustion of the air-fuel mixture occurs due to a spark from the spark plug.

Is a petrol engine SI or CI?

CI (Compression Ignition) engine is also known as a diesel engine. On the other hand, the SI (Spark Ignition) engine is known as a petrol engine.

What is the difference between fuel-injection petrol engines and diesel engines?

In a petrol engine, both air and fuel are combined and then compressed for ignition. However, in diesel engines air is compressed before injection of fuel in it.

What are the types of petrol injection systems?

• Types of fuel injection systems include:

• Single-point injector

• Gasoline direct injection

• Sequential injection system

• Multi-point fuel injection system.