Gas vapor recovery system

Posted On December 17th, 2019

The Evaporative Emission Control (EVAP) system is designed to prevent the release of gasoline vapour into the atmosphere. Vapours are formed when gasoline is heated in a fuel tank, as well as at reduced atmospheric pressure. Gasoline vapours are accumulated in the system when the engine starts, they are discharged into the intake manifold and burned in the engine. The system is used on all modern models of gasoline engines.

The gas vapour recovery system combines a coal adsorber, a purge solenoid valve and connecting pipelines.

The basis of the system design is an adsorber that collects gasoline vapours from the fuel tank. The adsorber is filled with granules of activated carbon, which directly absorb and retain gasoline vapour. The adsorber has three external connections:

  1. with a fuel tank (through it fuel vapour enters the adsorber);
  2. with the intake manifold (through it the adsorber is purged);
  3. with the atmosphere through an air filter or a separate valve at the inlet (though it creates the pressure drop necessary for purging).


The adsorber is released from the accumulated gasoline vapour by blowing (regeneration). To control the regeneration process, an adsorber purge solenoid valve is included in the EVAP system. The valve is the actuator of the engine management system and is located in the pipeline connecting the adsorber to the intake manifold.

The adsorber is purged under certain engine operating conditions (crankshaft speed, load). At idle and with a cold engine, no purge is performed.


At the command of the electronic control unit, the solenoid valve opens. Gasoline vapour in the adsorber is purged by vacuum in the intake manifold. They are sent to the collector and then burned in the combustion chambers of the engine.

The amount of gasoline vapour delivered is controlled by the valve opening time. In this case, the engine maintains an optimal ratio of air to fuel.

In turbocharged engines, the turbocharger does not create a vacuum in the intake manifold. Therefore, an additional two-way valve is included in the EVAP system, which activates and directs the fuel vapour when the adsorber is purged into the intake manifold (in the absence of boost pressure) or to the compressor inlet (in the presence of boost pressure).

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