What does EGR mean in automobiles?

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Automobile EGR refers to the Exhaust Gas Recirculation system, which involves recirculating a portion of the engine's exhaust gases back to the intake manifold, where they mix with fresh air-fuel mixture before re-entering the cylinders. Since exhaust gases contain a large amount of polyatomic gases such as CO2, which cannot combust but have high specific heat capacity and absorb significant heat, the maximum combustion temperature of the mixture in the cylinders is reduced, thereby decreasing the formation of NOx. EGR primarily functions in the following ways: 1. The CO2 and water vapor in EGR significantly increase the specific heat capacity of the working fluid, while the addition of exhaust gases also dilutes the oxygen concentration in the original mixture, slowing down the combustion rate and reducing both the peak and average temperatures during combustion. This disrupts the favorable conditions for NO formation, greatly reducing NOx emissions. 2. Since gasoline engines typically regulate load through quantity control, applying EGR in gasoline engines can correspondingly increase the intake air volume. An increase in the EGR rate can reduce the throttling losses under medium and low load conditions, thereby lowering the fuel consumption rate of the gasoline engine.