FUEL SUPPLY SYSTEMS

For an engine to work, fuel must burn properly with air. Combustion is simply the burning of fuel, and it needs three things: fuel, oxygen from air, and heat. The air-fuel ratio tells us how much air mixes with fuel—a perfect mixture is about 14-15 parts air to 1 part fuel by weight.

Petrol is lighter and burns quickly, making it ideal for cars like the Toyota Corolla used as taxis across Nigeria. Diesel is heavier, burns slower, and gives more power, which is why you see it in trucks and buses carrying goods from Lagos to Kano.

Both fuels have different properties affecting how engines run. Petrol evaporates easily while diesel doesn't, so they need different fuel systems and engine designs. Understanding these differences helps explain why petrol cars start faster than diesel ones in cold weather.

The fuel supply system moves petrol from your tank to the engine for burning. Two main types exist: gravity-feed systems, which rely on the fuel tank sitting higher than the carburetor so petrol flows downward naturally, and force-feed systems, which use pumps to push fuel under pressure. Most modern vehicles use force-feed because they're reliable and work regardless of tank position.

The carburetor mixes petrol with air in the right amounts. Simple carburetors work for basic engines, while multi-jet carburetors have several fuel passages for better performance at different speeds. Air filters prevent dust from entering the engine—critical in dusty Nigerian conditions where harmattan winds blow sand everywhere.

Mechanical fuel pumps use engine vibrations to push fuel; electrical pumps are more consistent and powerful. Mechanical pumps are cheaper but less reliable, while electric pumps last longer but cost more and need electrical maintenance.

Electronic Fuel Injection (EFI) is a modern system that sprays petrol directly into an engine's cylinders using electronic control. Unlike the old carburettor system, EFI uses sensors and a computer to manage fuel delivery precisely. The system includes an electric fuel pump, injectors, oxygen sensors, and an Engine Control Unit (ECU) that decides exactly how much fuel to spray and when.

The main merits are better fuel efficiency, improved engine performance, easier cold starting, and reduced emissions. Modern Nigerian vehicles like Toyota Camry and Honda Accord use EFI systems. The demerits include higher cost to repair, complex electronic components that require skilled technicians, and potential computer failures that leave you stranded.

Understanding EFI is crucial for modern mechanics because almost all vehicles manufactured today use this system instead of carburettors.

The diesel fuel supply system moves fuel from the tank to the engine's combustion chambers. Unlike petrol engines, diesel requires high-pressure injection. The fuel pump draws diesel from the tank and forces it through filters to remove impurities, then sends it to the injection pump at extremely high pressure. The injection pump times and controls fuel delivery, spraying it directly into each cylinder through injectors at precise moments. This is why diesel engines are so efficient—fuel burns completely under high compression.

Cold starting presents a challenge because diesel doesn't ignite easily in cold conditions. Many diesel engines, like those in Dangote trucks across Nigeria, use glow plugs that electrically heat the combustion chamber before starting. Once the engine runs, combustion heat takes over.

Understanding this system's layout and components is crucial for repair work and understanding diesel engine efficiency.