Evaporative Emission Control or EVAP System In Automobiles.

EVAP system in automobiles
Charcoal Canister

    Most of you would be unaware about EVAP systemEvap stands for " Evaporative Emission Control System”. The BS4 emission norms made it mandatory for vehicles to use EVAP systemsFor this, the vehicles had to be installed with charcoal canisters. Earlier the fuel tanks of vehicles were provided with small holes to prevent the formation of a vacuum. inside the fuel tank. When the fuel was supplied to the carburetor, the air used to rush inside to cover the space and hence the vacuum formation was prevented. The fuel vapour formed inside the tank used to escape to the atmosphere through the same holes.

    What Is Evaporative Emission?

    The fuel used in vehicles is very volatile. It use to form vapour even at normal temperature. These vapours than escape from the fuel tank through the ventilation hole and get mixed with air in the environment. They are very harmful for the environment and are a major contributor to vehicle pollution.

    How Does Evaporative Emission System Works?

    EVAP system in automobiles

                                                                                              The Evaporative Emission System consists of a charcoal canister. This canister contains activated charcoal. The charcoal is in powdered form so as to have a large surface area. The canister contains 4 pipes. One pipe is connected to fuel tank vent provided to remove fuel vapours. The pipe is provided with a rollover valve. The function of the rollover valve is to prevent the flow of liquid fuel to canister in case of accidents. The liquid fuel can degrade activated charcoal. The second pipe is called purge pipe. The purge pipe connects the canister to the carburetor or throttle body through a purge valve. The purge valve is a non-return valve, which allows the flow in only one direction i.e. from the canister to the carburetor or throttle body. One more pipe called canister overflow pipe is provided to remove any liquid fuel present inside the canister. It is also provided with a pipe called vent pipe which helps in air supply. At the time of inlet stroke, the vacuum inside the intake manifold sucks the air through the purge pipe, which ultimately creates a suction in vent pipe. This suction pulls the air through  vent pipe . The sucked air moves through charcoal inside the canister. While moving through the canister it carries the particles of fuel trapped in charcoal. This air is sucked inside carburetor or throttle body through the purge pipe. In this way, the EVAP system prevents the evaporative emissions.

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