Fuel Vapor Canister

Canister is a pollution control device used mainly in gasoline fuel tanks to prevent the vapors of the fuel escape from the tank. Gasoline gets easily vaporized, and evaporated gasoline can increase the emissions because it is a mixture of hydrocarbons (HC) which is harmful for both environment and humans. This system is also known as Evaporative Emission Control System (EVAP) or fuel vapor canister or carbon canister.

Fuel vapor canisters were first used in the mid-1970s and it significantly reduced the HC emissions. Gases escaping from the tank or engine result in HC emissions.

To prevent the evaporated fuel to escape unburned, fuel vapor canister is used to trap all the vapors and then store and use it later when the engine is switched ON. A fuel vapor canister only works when the engine is OFF.

Design of Canister:

There is an inlet port and an outlet port. The canister is filled with charcoal. The charcoal traps the gas and then sends it out via the outlet port. When the gasoline vaporizes, the vapors from the tank escape through a vent line and then reach the canister through the inlet port. The outlet port is connected to a purge valve which prevents the fuel from entering the inlet manifold unless the engine is switched ON.

A carburetor vent line is provided for the fuel bowl in the carburetor. The fuel in the carburetor bowl will vaporize when the temperature rises. The vaporized fuel is supplied to the canister through the carburetor vent line.

The canister is provided with a purge air line at the bottom which allows the air from the atmosphere to enter the canister and form a fuel-air mixture.

Working of a Fuel Vapor Canister:

The evaporated gases reach the canister through the vent port and reach the carbon canister. The gases are trapped inside due to its properties to trap hydrocarbons. The gases are stored in the canister. When the engine is switched ON, suction is created in the intake manifold which prompts the purge valve to open and this allows the air to be sucked inside the canister through an air filter. The air from the purge air line pushes the gasoline vapors from the canister to the intake manifold. The air-fuel mixture is then supplied and burned inside the combustion chamber. The canister stops working when the engine is switched ON. Fuel vapor canister can only be used in a vehicle having a carburetor.