The Evaporative Emission Control System (EVAP) is a system in cars that prevents fuel vapours in the fuel tank from escaping into the atmosphere. The fuel vapours due to lesser density evaporate all the time in the fuel tank. EVAP captures and stores these vapours, they are transferred to the combustion chamber once the engine starts. Let’s find out about the components of an EVAP and how it functions.
What is an Evaporative Emission Control System (EVAP)?
An Evaporative Emission Control System is designed to minimise or completely stop the release of vaporised hydrocarbons (HC) into the atmosphere. The atmosphere’s reaction with the HC vapours results in the development of photochemical smog and ground-level ozone, which promotes air pollution.
How Does an EVAP System Work?
Fuel vapours and other emissions are captured by the evaporative emission control (EVAP) system. The excess vapours, generated upon evaporation of fuel inside the fuel tank, are transferred to the charcoal EVAP canister. They are stored in the EVAP canister until the engine starts and fuel is required for normal air-fuel combustion.
When it is time to transfer the fuel vapours, a valve creates the required vacuum which draws the vapours into the combustion chamber. Through the vents and valves, fresh air is also pulled in to combine with the vapours for improved combustion. These systems can be managed mechanically or, as is the case with the majority of modern vehicles, via the car’s computer.
Components of an EVAP System
The components of an Evaporative Emission Control System are detailed below.
Fuel Tank
It is a part of the EVAP and has space for expansion at the top. It is because when fuel expands on a hot day, the fuel won’t spill and prevent EVAP system leaks as well.
Gas Cap
It covers the fuel tank’s filler neck from the environment outside. The most common reason for the activation of the check engine light is a damaged or missing gas cap. It is recommended to tighten the gas cap after fueling.
Liquid-Vapour Separator
The separator is a part of the EVAP system. It keeps away fuel from the EVAP canister to prevent exhausting its vapours storing capacity.
EVAP Canister
The tank vent line connects the EVAP canister to the fuel tank. Activated charcoal is stored inside the EVAP canister, and it functions like an absorbent to hold fuel vapours until the purge valve opens. A bad EVAP canister can be detected when the check engine light activates or due to poor engine performance.
Purge Valve / Sensor
The purge valve or sensor allows the right amount of fuel vapours to transfer from the EVAP canister to the engine’s intake manifold.
Vent Control Valve
It allows fuel vapours to flow into the EVAP canister from the fuel tank.
Fuel Tank Pressure Sensor
This sensor checks the pressure in the fuel tank. It generates a signal upon detection of high or low pressure in the tank. A bad fuel pressure sensor results in hard engine starts, engine stalling and poor fuel mileage.
Vent Hoses
These hoses allow the flow of fuel vapours to the components of the EVAP system.
Fuel Level Sensor
It monitors the fuel level in the tank.
FAQs
What is an EVAP leak?
An EVAP leak indicates that the fuel vapours are leaking into the atmosphere even when the engine is switched off.
How do you diagnose an EVAP leak?
The check engine light is the primary indicator of EVAP leaks. A typical problem is a loose gas cap. In modern vehicles, the check engine light turns on when the ECU detects an issue with the EVAP system. To diagnose the issue, use an OBD car scanner or take your shop to a mechanic for inspection.
Is it safe to drive with an EVAP leak?
Technically, it is safe to drive with an EVAP leak, but it is not recommended at all. This is because an EVAP leak exposes the environment to harmful fuel vapours.
That is all about the Evaporative Emission Control System, its components and its functioning. The EVAP system is present in all modern vehicles but many motorists are unaware of it. Make sure that the EVAP system is regularly maintained for healthy car performance. That said, if despite timely car maintenance your car is posing issues, you should consider switching to another one. Explore these used cars for sale in the UAE and have your ideal pick.
For more information on car parts and accessories, stay tuned to the UAE’s leading auto blog.
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