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How do gasoline vapour-control systems keep fuel vapours from escaping into the air?

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Labeled cross-sectional diagram of a V-type gasoline engine for an automobile, showing internal components such as pistons, crankshaft, camshaft, intake and exhaust valves, connecting rods, spark plugs, and intake manifold. — gasoline engine Cross section of a V-type engine.

To prevent fuel vapours from escaping into the atmosphere, modern vehicles utilize a sealed fuel system combined with an evaporative emission control system.

The process functions through the following steps:

Containment: The fuel tank is sealed with a specialized cap to prevent direct venting of fumes.1
Separation: Vapours travel from the tank to a vapour separator, which returns any raw liquid fuel back to the tank while directing the remaining vapours toward a storage canister.1
Storage: The vapours are channeled into a canister filled with activated charcoal, which acts as a storehouse capable of holding a significant amount of fuel vapour.1
Purging and Combustion: When the engine is running, a vacuum draws the stored vapours from the charcoal canister through a filter and into the combustion chamber. There, the vapours are burned along with the standard fuel-air mixture, effectively eliminating them as pollutants.1