What is “Evaporative emission control”?
Evaporative Emission Control (EVAP) systems are designed to prevent fuel
vapors from escaping into the atmosphere from a vehicle's fuel system. These
systems are crucial for reducing air pollution and meeting environmental
regulations.
Basic Function
The EVAP system captures and stores fuel vapors from the fuel tank and fuel
system components. It then routes these vapors back into the engine’s intake
manifold to be burned during combustion, rather than allowing them to escape
into the air.
This canister contains activated charcoal, which absorbs and stores fuel vapors
from the fuel tank and fuel lines. It is a key component of the EVAP system.
Purge Valve (Purge Solenoid):
The purge valve controls the flow of stored vapors from the charcoal canister to
the engine’s intake manifold. It opens at appropriate times to allow vapors to be
drawn into the engine for combustion.
Vent Valve (Vent Solenoid):
The vent valve controls the flow of air into and out of the charcoal canister,
ensuring proper pressure balance and vapor management within the fuel
system.
Fuel Cap:
The fuel cap is designed to seal the fuel tank and prevent vapor leakage. Some
caps are equipped with pressure-relief valves to manage excess pressure.
Vapor Capture:
When the engine is off, fuel vapors from the fuel tank and fuel lines are directed
into the charcoal canister, where they are absorbed and stored by the activated
charcoal.
Vapor Purging:
When the engine is running and conditions are appropriate (typically during
steady driving conditions), the engine control unit (ECU) opens the purge valve.
This allows the stored vapors to be drawn from the charcoal canister into the
engine’s intake manifold.
Combustion:
The fuel vapors are mixed with the air-fuel mixture in the intake manifold and
burned in the combustion chamber. This reduces the amount of raw fuel vapors
released into the atmosphere.
Pressure Management:
The vent valve manages the flow of air into and out of the charcoal canister,
ensuring that the system maintains proper pressure and functions efficiently.
Benefits
Reduced Emissions: EVAP systems significantly reduce the emission of volatile
organic compounds (VOCs), which contribute to smog and air pollution.
Improved Air Quality: By capturing and burning fuel vapors, EVAP systems help
improve overall air quality and reduce the environmental impact of vehicles.
Compliance with Regulations: EVAP systems are essential for meeting stringent
emission regulations and standards set by environmental agencies
