What is the purpose of the exhaust gas recirculation (EGR) component in emission control?

• A. To recirculate exhaust gases into the intake manifold
• B. To inject fuel into exhaust
• C. To increase exhaust backpressure
• D. To decrease engine temperature

Answer: (A)

The goal of exhaust gas recirculation is to lower nitrogen oxide (NOx) emissions by reducing the peak combustion temperature inside the cylinder. It achieves this by routing a portion of the exhaust gases back into the intake manifold, where they mix with the incoming air. The inert gases dilute the air-fuel mixture and absorb heat, so the flame temperature is lower, which slows the rate of NOx formation. The EGR gas is often cooled before entering the intake to maximize cooling of the charge. This is why the recirculation setup is effective for emission control: it lowers combustion temperatures rather than injecting fuel into exhaust or directly increasing backpressure, and it doesn’t primarily serve to cool the engine as a whole.