What is the primary function of an EGR (Exhaust Gas Recirculation) valve?

The primary function of an EGR valve is to reduce nitrogen oxide emissions. In internal combustion engines, nitrogen oxides (NOx) are pollutants formed at high combustion temperatures, leading to increased environmental concern and regulatory standards. The EGR system mitigates this by recirculating a portion of the exhaust gas back into the engine's intake manifold. This process dilutes the intake air-fuel mixture, which lowers the combustion temperature. By reducing peak combustion temperatures, the formation of nitrogen oxides is significantly decreased, helping to meet emissions regulations and improve air quality.

This functionality aligns with the role of EGR systems in modern vehicles, which often face stringent emissions standards. While the other options may relate to different aspects of engine performance, they do not describe the primary role of the EGR valve.