What emission gas is controlled by the EGR valve?

The emission gas that is controlled by the EGR (Exhaust Gas Recirculation) valve is nitrogen oxides, commonly referred to as NOx. The primary function of the EGR valve is to redirect a portion of an engine’s exhaust gas back into the intake manifold. This process lowers the combustion temperature inside the engine, as introducing exhaust gases effectively dilutes the air-fuel mixture. By reducing the peak combustion temperatures, the formation of NOx—compounds that contribute significantly to smog and air quality issues—is minimized.

Nitrogen oxides are harmful pollutants produced primarily during high-temperature combustion processes, such as in gasoline and diesel engines. The implementation of EGR systems is a critical strategy employed by manufacturers to meet stringent emissions regulations and improve air quality by curbing NOx emissions.

Other gases listed in the options, such as CO2 (carbon dioxide), hydrocarbons (HC), and SOx (sulfur oxides), are managed by different engine control technologies or processes. CO2 is a greenhouse gas associated with fuel consumption, HC refers to unburned fuel that can contribute to smog, and SOx are often derived from sulfur in fuels. Each of these gases requires specific controls and mitigation strategies that do not involve