What is the role of Exhaust Gas Recirculation (EGR)?

• A. It reduces HC emissions during engine warm-up.
• B. It increases CO2 emissions to meet standards.
• C. It is a post-combustion emission component that helps reduce NOx emissions during engine operation.
• D. It cools the exhaust to improve mileage.

Answer: (C)

Exhaust Gas Recirculation reduces NOx by sending a portion of the exhaust back into the intake. This dilutes the air-fuel mixture with inert exhaust gas, lowering the peak combustion temperature and slowing the rate at which nitrogen and oxygen react to form NOx. Because NOx formation is most severe at high temperatures, this temperature reduction during engine operation helps meet emissions standards. It’s a control strategy used during normal operation rather than a post-treatment device like a catalytic converter, and its primary effect is NOx reduction rather than cooling the exhaust or directly affecting HC emissions during warm-up.