How does a car's fuel system work?

The fuel system of an automobile moves fuel from a fuel tank to the engine, where fuel is combined with air and introduced into the cylinder chambers. Combustion of the fuel in the cylinders produces the energy that powers the engine. Modern fuel systems are controlled by complex electronics, but their basic operation is simple.

Fuel Tank

A vehicle’s fuel, either gasoline or diesel fuel, is held in a storage tank which is usually located in the rear of passenger cars. Fuel enters the tank via a filler tube that opens on the exterior of the car, and a system of vents allows fuel vapor to escape and maintain proper pressure within the tank. Baffles inside the tank minimize sloshing of fuel when the vehicle is in motion, and a sensor measures the fuel level and displays it on the fuel gauge inside the cabin. An outlet line directs fuel to the engine, and in most newer cars, the fuel pump is located inside the fuel tank.

Fuel Pump and Filter

Fuel is moved from the tank to the engine by the action of a fuel pump. In most newer cars, the fuel pump is powered electrically and begins to operate when the ignition switch is activated. Older vehicles may employ a mechanical pump that is powered by the action of the engine. Fuel is pumped through fuel lines, made from rigid steel, flexible braided steel or corrosion-resistant rubber, to the engine. One or more fuel filters removes particulate contaminates from the fuel to avoid clogging the fuel system within the engine.

Carburetor and Fuel Injectors

In older cars, fuel is pumped through a carburetor, a mechanism that mixes the fuel with air in the proper proportion before introducing it into the cylinder chambers. Modern cars use a series of electric fuel injectors which spray a fine mist of fuel into the chambers; fuel injectors operate more reliably and efficiently than carburetors. Once introduced into the cylinder chamber, fuel is ignited by a spark, producing the explosion that powers the engine.

Emission Control System

Cars manufactured after 1970 vent fuel vapors from the fuel tank into the engine, allowing the vapors to be burned before being vented into the air, thereby reducing the amount of pollutants released into the atmosphere. Modern cars are also equipped with sensors that monitor the oxygen content of exhaust gases, manifold pressure, the mass of air flowing into the engine and other parameters in order to adjust the air/fuel mixture to ensure cleaner, more efficient burning of fuel.